19,99 €
Mehr erfahren.
- Herausgeber: John Wiley & Sons
- Kategorie: Fachliteratur
- Sprache: Englisch
Become a disease detective with this easy-to-understand resource Epidemiology For Dummies is packed with key concepts, practical applications, and real-life examples in the study of disease transmission and control. It's a must-have for students in all public-health-related fields, and for curious learners, too. This Dummies guide will help you conquer even the trickiest epidemiological concepts. In this introduction to the fascinating, complex science, you'll learn--in terms anyone can understand--all the basic principles of epidemiology, plus how those concepts translate to public health outcomes and policy decisions. * Learn the basic principles and concepts of epidemiology * Discover real-world examples and public health threats * Understand the complex social factors that influence health * Embark on a public health career or just pass your epidemiology course Anyone who wants or needs to understand the fundamentals of epidemiology and the science behind public health will love Epidemiology For Dummies.
Sie lesen das E-Book in den Legimi-Apps auf:
Seitenzahl: 579
Veröffentlichungsjahr: 2023
Ähnliche
Epidemiology For Dummies®
Published by: John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030-5774, www.wiley.com
Copyright © 2023 by John Wiley & Sons, Inc., Hoboken, New Jersey
Media and software compilation copyright © 2023 by John Wiley & Sons, Inc. All rights reserved.
Published simultaneously in Canada
No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning or otherwise, except as permitted under Sections 107 or 108 of the 1976 United States Copyright Act, without the prior written permission of the Publisher. Requests to the Publisher for permission should be addressed to the Permissions Department, John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, (201) 748-6011, fax (201) 748-6008, or online at http://www.wiley.com/go/permissions.
Trademarks: Wiley, For Dummies, the Dummies Man logo, Dummies.com, Making Everything Easier, and related trade dress are trademarks or registered trademarks of John Wiley & Sons, Inc. and may not be used without written permission. All other trademarks are the property of their respective owners. John Wiley & Sons, Inc. is not associated with any product or vendor mentioned in this book.
LIMIT OF LIABILITY/DISCLAIMER OF WARRANTY: WHILE THE PUBLISHER AND AUTHORS HAVE USED THEIR BEST EFFORTS IN PREPARING THIS WORK, THEY MAKE NO REPRESENTATIONS OR WARRANTIES WITH RESPECT TO THE ACCURACY OR COMPLETENESS OF THE CONTENTS OF THIS WORK AND SPECIFICALLY DISCLAIM ALL WARRANTIES, INCLUDING WITHOUT LIMITATION ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. NO WARRANTY MAY BE CREATED OR EXTENDED BY SALES REPRESENTATIVES, WRITTEN SALES MATERIALS OR PROMOTIONAL STATEMENTS FOR THIS WORK. THE FACT THAT AN ORGANIZATION, WEBSITE, OR PRODUCT IS REFERRED TO IN THIS WORK AS A CITATION AND/OR POTENTIAL SOURCE OF FURTHER INFORMATION DOES NOT MEAN THAT THE PUBLISHER AND AUTHORS ENDORSE THE INFORMATION OR SERVICES THE ORGANIZATION, WEBSITE, OR PRODUCT MAY PROVIDE OR RECOMMENDATIONS IT MAY MAKE. THIS WORK IS SOLD WITH THE UNDERSTANDING THAT THE PUBLISHER IS NOT ENGAGED IN RENDERING PROFESSIONAL SERVICES. THE ADVICE AND STRATEGIES CONTAINED HEREIN MAY NOT BE SUITABLE FOR YOUR SITUATION. YOU SHOULD CONSULT WITH A SPECIALIST WHERE APPROPRIATE. FURTHER, READERS SHOULD BE AWARE THAT WEBSITES LISTED IN THIS WORK MAY HAVE CHANGED OR DISAPPEARED BETWEEN WHEN THIS WORK WAS WRITTEN AND WHEN IT IS READ. NEITHER THE PUBLISHER NOR AUTHORS SHALL BE LIABLE FOR ANY LOSS OF PROFIT OR ANY OTHER COMMERCIAL DAMAGES, INCLUDING BUT NOT LIMITED TO SPECIAL, INCIDENTAL, CONSEQUENTIAL, OR OTHER DAMAGES.
For general information on our other products and services, please contact our Customer Care Department within the U.S. at 877-762-2974, outside the U.S. at 317-572-3993, or fax 317-572-4002. For technical support, please visit https://hub.wiley.com/community/support/dummies.
Wiley publishes in a variety of print and electronic formats and by print-on-demand. Some material included with standard print versions of this book may not be included in e-books or in print-on-demand. If this book refers to media such as a CD or DVD that is not included in the version you purchased, you may download this material at http://booksupport.wiley.com. For more information about Wiley products, visit www.wiley.com.
Library of Congress Control Number: 2023931886
ISBN: 978-1-394-17070-8 (pbk); ISBN: 978-1-394-17071-5 (ebk); ISBN: 978-1-394-17072-2 (ebk)
Epidemiology For Dummies®
To view this book's Cheat Sheet, simply go to www.dummies.com and search for “Epidemiology For Dummies Cheat Sheet” in the Search box.
Table of Contents
Cover
Title Page
Copyright
Introduction
About This Book
Foolish Assumptions
Icons Used in This Book
Beyond This Book
Where to Go from Here
Part 1: Getting Started with Epidemiology
Chapter 1: Entering the World of Epidemiology
Introducing Epidemiology
Recognizing How Numbers Can Help Study Disease
Focusing on Prevention Rather Than a Cure
Delving into Study Finding
Figuring Out What You Know about Epidemiology: Some Q&As
Chapter 2: Epidemiology 101 — Understanding the Basics
Defining Epidemiology — What to Expect from Your Coursework and Beyond
Realizing Why Epidemiology Is Important
Understanding How Epidemiology Tools Are Applied
Contrasting the Roles of a Physician and Epidemiologist
Seeking Medications
Considering How a Disease Is Transmitted
Searching for Sources of Epidemiologic Data
Chapter 3: Exploring the Development of Epidemiological Thinking
Meeting Hippocrates — the First Epidemiologist
Tackling the Miasma Theory
Examining Contributions to Medicine and Public Health – Thomas Sydenham
Using Concepts of Environmental Epidemiology — Noah Webster
The Germ Theory — Washing Hands Is Essential
Working on Workers’ Diseases — Bernardino Ramazzini
The Birth of Vital Statistics: No Labor Pains Involved
Examining the Start of Epidemiology and Public Health in the United States
Reforming Public Health in England
Looking At Modern Epidemiology
Chapter 4: Eyeing the Milestones in Public Health
Finding the Treatment of Scurvy — James Lind
Discovering Sources of Cholera in London’s Golden Square — John Snow
Uncovering Causes of Pellagra — Joseph Goldberger
Describing the 1918 Influenza Pandemic
Eradicating Smallpox
Finding Smoking as a Cause of Lung Cancer
Feeling the Beat of the Framingham Heart Study
Chapter 5: Recognizing Diseases and Controlling Them
Identifying the Modes of Transmission
Eyeing the Chain of Infection: Can You Break It?
Examining the Natural History of Disease
Listing Common Notifiable Diseases
Controlling Waterborne Diseases
Tackling Problems of Airborne Infections
Curving Vector-Borne Diseases
Limiting Parasitic Infections
Controlling Sexually Transmitted Infections
Dealing With Emerging Infectious Diseases
Identifying Diseases Caused by Heavy Metals
Part 2: Understanding Disease Causation
Chapter 6: Tackling the Epidemiologic Triangle
Scrutinizing an Acute Disease Model
Inspecting a Chronic Disease Model
Understanding How Climate Change Can Affect Health
Chapter 7: Inspecting Descriptive Epidemiology: Person, Place, and Time
Knowing Person Factors
Focusing on Place Factors
Checking Time Factors
Chapter 8: Viewing Disease Patterns
Defining the Epidemiologic Transition
Grasping Why Epidemiologic Transition Happens
Studying Some Chronic Health Conditions
Understanding How Epidemiologic Transition Affects Healthcare
Chapter 9: Linking Demography and Disease
Defining Demography — Why It’s Important
Using Demographic Data to Identify Population at Risk
Tackling Population Pyramids: Not the Ones in Egypt
Projecting Population – Simple Math
Chapter 10: Digging into Math: Calculating Rates and Risks
Addressing Some Basics When Calculating Descriptive Epidemiology
Calculating Crude Morbidity and Crude Mortality Rates
Figuring Out Commonly Used Rates
Measuring Incidence and Prevalence
Standardizing Rates
Part 3: Prevention Is Better Than a Cure
Chapter 11: Focusing on the Levels of Prevention
Identifying Primary Prevention
Recognizing Secondary Prevention
Examining Tertiary Prevention
Chapter 12: Preventing Disease with Vaccine
Getting the Lowdown on Immunity
Planning Shots for Children, from Birth through Adolescence
Looking Closer at Cancer-Preventing Vaccines
Identifying Common Vaccine-Preventable Diseases
Preventing Disease for World Travelers
Chapter 13: Recognizing Methods of Disease Surveillance
Differentiating between Survey, Surveillance, and Monitoring
Defining the Types of Surveillance
Conducting Surveillance: The How-to
Chapter 14: Investigating an Outbreak
Conducting an Epidemic Investigation
Digging Out Cases by Surveillance, Step-by-Step
Using Makeshift Hospitals
Walking through an Outbreak Investigation
Chapter 15: Identifying Disease by Screening
Defining Screening
Naming Ingredients of a Good Screening Test
Looking Closer at Some Common Screening Programs
Evaluating Screening Tests
Part 4: Examining a Study Finding
Chapter 16: Figuring Out Whether an Association Is Causal
Establishing Causality
Understanding Hill’s Criteria for Causality
Making Rothman’s Causal Pie
Chapter 17: Investigating the Types of Epidemiologic Studies
Looking At the Anatomy of Epidemiologic Studies
Conducting a Cross-Sectional Study
Plotting a Case-Control Study
Leading a Cohort Study
Figuring Out an Ecological Study
Developing a Questionnaire
Chapter 18: Encountering Bias and Confounding
Defining Bias
Clarifying What Confounding Means
Reviewing Bias-Affecting Research Findings
Steering Clear of Bias in the Initial Stages of Research
Controlling for Confounders
Chapter 19: Focusing On Ethics in Health Research
Comprehending the Evolution of Ethical Norms in Research
Grasping the Importance of a Code of Ethics
Using Informed Consent
Part 5: The Part of Tens
Chapter 20: Ten Careers with a Degree in Epidemiology
Epidemiologist
Environmental Epidemiologist
Surveillance Data Analyst and Epidemiologist
Infection Control Officer
Research Scientist
Research Associate
Data Analyst
Program Manager
Chief Medical/Quality Officer
Data and Research Coordinator
Chapter 21: Ten Tips for Acing Your Epidemiology Classes
Ask and Answer Questions in Class
Practice, Practice, and Practice
Take Good Class Notes
Get Information Online
Apply the Knowledge
Make a Cheat Sheet
Use a Scientific Calculator
Memorize Some Definitions and Steps
Get Involved in Research
Participate in Group Work
Glossary
Index
About the Author
Connect with Dummies
End User License Agreement
List of Tables
Chapter 2
TABLE 2-1 Differences between a Physician and an Epidemiologist
TABLE 2-2 Identifying Diseases by a Physician and an Epidemiologist
TABLE 2-3 Top Ten Commonly Used Prescribed Drugs in the U.S.
Chapter 3
TABLE 3-1 Pioneers of Public Health in America, 1610–1925
Chapter 4
TABLE 4-1 Cholera Deaths from Two Water Supplies in Soho, London over Seven Week...
Chapter 6
TABLE 6-1 Type of Agents and the Diseases Caused by Agents
Chapter 7
TABLE 7-1 Diseases and Age Groups at Risk
TABLE 7-2 Estimated Life Expectancy at Birth (in Years) by Gender in 2022
Chapter 8
TABLE 8-1: Top Ten Killer Diseases in Selected Developing Countries
TABLE 8-2: American Heart Association Guidelines for Life’s Simple Seven (LSS)
Chapter 10
TABLE 10-1 Data for Calculating Crude Birth Rate and Crude Death Rate
TABLE 10-2 Data for Calculating Age-Specific Death Rates
TABLE 10-3 Data for Calculating Cause-Specific Death Rates
TABLE 10-4 Calculating Homicide Rates in Five States
TABLE 10-5 Proportionate Mortality (Percentage) of Top Ten Causes of Deaths, Uni...
TABLE 10-6 Covid-19 Cases, Deaths, and Case-Fatality Rates, January 23, 2023
TABLE 10-7 Distribution of Deaths by Age-Group and Person-Year in the Study Popu...
TABLE 10-8 Distribution of Deaths by Age-Group and Person-Year in the Standard P...
Chapter 12
TABLE 12-1 Vaccination Schedule for Infants from Birth to 15 Months Old
TABLE 12-2 Vaccination Schedule for Children and Teens
Chapter 14
TABLE 14-1 Calculating Attack Rates
TABLE 14-2 Distribution of Sick and Well People
TABLE 14-3 Food-Specific Attack Rates
TABLE 14-4 Cross-Table Analysis for Egg Salad and Beverage Consumed
Chapter 15
TABLE 15-1 Common Terms Used in Screening
TABLE 15-2 Example of True Positive, False Positive, False Negative, and True Ne...
TABLE 15-3 Concept of Sensitivity, Specificity, and Predictive Values
TABLE 15-4 Data Illustrating Sensitivity, Specificity, and Predictive Values
TABLE 15-5 Evaluation of Predictive Values of a Screening Test
TABLE 15-6 Pap Smear Results of 1,000 Women Screened for Cervical Cancer
TABLE 15-7 Relationship between Prevalence and Predictive Value
TABLE 15-8 Relationship between Prevalence and Predictive Value
Chapter 16
TABLE 16-1 Use of Relative Risk to Identify an Association
Chapter 17
TABLE 17-1 Pros and Cons of a Cross-Sectional Study
TABLE 17-2 Pros and Cons of a Case-Control Study
TABLE 17-3 The Association of Stomach Ulcer with
Helicobacter Pylori
Infection
TABLE 17-4 Breast Cancer Occurrence among Women with or without DDT Exposure
TABLE 17-5 Pros and Cons of a Cohort Study
TABLE 17-6 Pros and Cons of an Ecological Study
List of Illustrations
Chapter 4
FIGURE 4-1: Mortality from the 1918 influenza pandemic in the United States.
Chapter 5
FIGURE 5-1: The chain of disease transmission.
FIGURE 5-2: The natural history of a disease.
Chapter 6
FIGURE 6-1: The agent-host-environment model.
FIGURE 6-2: An extended model of agent-host-environment: Case of heart disease....
Chapter 7
FIGURE 7-1: A map showing countries where malaria is prevalent.
FIGURE 7-2: A GIS map showing percentage of children with high blood levels of ...
FIGURE 7-3: Pattern of the epidemic curve.
FIGURE 7-4: Pattern of an epidemic curve of a propagated source of origin.
Chapter 8
FIGURE 8-1: Changes in leading causes of death from 1900 to 1998 in the United ...
Chapter 9
FIGURE 9-1: The stages of demographic transition in the world.
FIGURE 9-2: Population pyramids of India and the United States, 2022.
Chapter 14
FIGURE 14-1: The seasonality of cholera epidemics.
Chapter 15
FIGURE 15-1: A flow chart showing steps of screening and the outcome.
FIGURE 15-2: Validity and reliability of a screening test.
FIGURE 15-3: The effect of changing cutoff points on sensitivity and specificit...
Chapter 16
FIGURE 16-1: The association of risk of type 2 diabetes with BMI categories.
FIGURE 16-2: Relation between statuses of cigarette smoking with cumulative ris...
FIGURE 16-3: Comparison of incidence and mortality of prostate cancer with race...
FIGURE 16-4: Multifactorial causes of myocardial infarction.
FIGURE 16-5: A dose-response curve.
FIGURE 16-6: Correlation between dietary fat intake and long-term risk of coron...
Chapter 17
FIGURE 17-1: The different types of epidemiologic studies.
FIGURE 17-2: Hierarchy of epidemiologic studies based on quality and risk of bi...
FIGURE 17-3: A cross-sectional study model.
FIGURE 17-4: A case-control study model.
FIGURE 17-5: A prospective cohort study model.
Guide
Cover
Title Page
Copyright
Table of Contents
Begin Reading
Glossary
Index
About the Author
Pages
iii
iv
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
343
344
345
346
347
348
349
350
351
352
353
354
355
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
379
380
381
382
Introduction
As a beginner in public health, you may be on a quest to know about diseases that are affecting your community, other countries, and the world. If you desire to build a career in a field of epidemiology, you want to know more about what causes certain diseases and how they’re transmitted, or as a public health professional, you want to advise people about disease prevention.
You’ve come to the right place. Epidemiology has been a hot topic in the past few years with the Covid-19 pandemic, but there’s so much more to it. Getting a degree in epidemiology is a good choice because the concepts and skills of epidemiology will prepare you for plenty of jobs in public health. Even if you aren’t a researcher or a data analyst, epidemiology can help you get a sense about numbers when you hear that the Covid-19 rates are rising or coming down, or when you hear that Forest County of Hattiesburg, Mississippi is the hot spot of lead poisoning.
About This Book
Epidemiology For Dummies emerged from the needs of undergraduate and graduate students in public health, especially in the field of epidemiology. During the Covid-19 pandemic, almost all face-to-face classes were closed and classes were only offered online. Some students faced challenges in fully understanding some difficult topics during this online format.
This handy guide isn’t a textbook or workbook in epidemiology. Rather, I wrote this book based on my decades of experience in practicing medicine, conducting health research, and teaching public health for undergraduate as well as graduate students to help explain the concepts of epidemiology in plain English with plenty of real-life examples, calculations, and illustrations.
Here you can read about an array of concepts, starting from Epidemiology 101 to more advanced research methods to ethics in conducting human research. I focus on the following areas:
The history of the development of public health and epidemiology
The epidemiologic triangle
Person-place-time distribution of diseases
Causal association and Hill’s criteria
The three levels of prevention
Vaccine-preventable diseases
Disease surveillance
Steps of outbreak investigations
Screening methods
Epidemiologic study designs
Bias and confounding
Population projection
Ethics in human research
I also provide step-by-step explanations and answers to practical issues like the following:
Investigating outbreaks and analyzing data
Solving problems of sensitivity, specificity, and predictive value
Calculating commonly used rates, ratios, and proportions
Calculating incidence, prevalence, and standardized mortality ratio (SMR)
Calculating country-level data for population projection
Foolish Assumptions
When writing this book, I’ve made a few assumptions about you, my dear reader. I made the following assumptions:
You’re bored or somewhat disappointed by reading textbooks with small fonts, full of concepts after concepts, with few examples of topics that don’t provide real-life examples of epidemiologic applications.
You’ve struggled understanding some of the technical terms and concepts in epidemiology, but you see your future working in public health.
You’re excited about applying what you’ve studied in your epidemiology courses, but you need a little extra help with the calculations.
You’ve been working a few years in a health department and you’ve faced many issues, such as choosing the right study design based on your resources, preparing a questionnaire, or investigating and controlling an epidemic.
You’re a silent learner, and you don’t ask questions in a class.
Icons Used in This Book
Throughout this book, you can find icons — small pictures next to the text that point out extra-important information. Here’s what they all mean:
For gems of accumulated wisdom — quite often the kind learned by painful experience! — follow this icon.
Consider this icon like a stop sign. When you see it, stop and pay extra attention because you might make a mistake — perhaps in a math calculation or something extra important — if you’re not careful enough.
You’re trying to do things correctly and efficiently. Problem is, you may not always know what’s right and what isn’t. When you see this icon, pay attention to the text.
This icon is used for more advanced material that you don’t need to read to understand the concept at hand. It’s information that’s interesting but not absolutely essential.
This icon points out concepts with practical examples, some from my own research.
Beyond This Book
This book is chock-full of tips and other pieces of helpful advice you can use as you study epidemiology. I provide links where you can go online for more information. In addition, check out the book’s Cheat Sheet at www.dummies.com and search for “Epidemiology For Dummies Cheat Sheet” for information to reference on a regular basis.
Where to Go from Here
This book represents a starting point for concepts and uses of epidemiology. Your new learning curve in public health is just beginning. So, now what? You can flip through the Index or Table of Contents to find a subject that interests you.
Or you can turn to whatever section looks to have the answers and information you’re wanting most. No matter where you start, you can read a section or two, stop, and then come back when you need more guidance. I tell my students, “Epidemiology is easier than you think and more fun than you can imagine.”
Part 1
Getting Started with Epidemiology
IN THIS PART …
Gain a basic knowledge about infection and infecting agents such as bacteria, viruses, parasites, yeasts, molds, and others; how diseases occur, and why you are
not
sick all the time despite living in a world with so many infecting agents.
Get background information about how the science of modern-day epidemiology came into play through different stages of legendary works in the field.
Understand the scope of epidemiology, two major functions of epidemiology, and the importance of epidemiology in measuring health status, searching for disease causation, and controlling and preventing diseases and events in humans.
Identify sources of epidemiologic data such as the Centers for Disease Control and Prevention (CDC), the World Health Organization (WHO), census data, vital statistics, and others.
Explore older and modern theories of diseases causation and important contributions of people in laying foundation and the development of different branches of public health.
Uncover milestones in public health, such as James Lind’s study of finding the treatment for scurvy, the cholera investigation of John Snow, Joseph Goldberger’s study of the cause of pellagra, the famous influenza pandemic, the eradication of smallpox, the connection between smoking and cancer, the development of theories of causal association, and more.
Recognize the means and ways of controlling several common infections, such as waterborne diseases, airborne diseases, vector-borne diseases, parasitic diseases, and sexually transmitted infections.
Chapter 1
Entering the World of Epidemiology
IN THIS CHAPTER
Introducing the concepts of epidemiology
Finding out about uses of numbers
Focusing on prevention
You’re about to enter the wonderful world of epidemiology — an adventure of hunting for five million trillion trillion (that’s a five with 30 zeroes after it) bacteria, about six million parasites, and nearly 7,000 virus species that are prevailing in the world. Thank goodness not all of them are harmful to you. The vast majority of them either live on the planet or inside you harmlessly or keep at bay like microscopic superheroes. Fewer than 100 species of bacteria, 300 species of parasitic worms, about 70 species of protozoa, and more than 200 viruses are known to cause disease in humans.
Most of the disease agents, which are infectious in nature, are controllable, either by antibiotics, vaccines, or by other public health preventive measures, such as personal hygiene, safe water supply, proper sanitation, healthy food habits, and by improving your resistance to infecting agents.
This chapter gives you an overview of this world of epidemiology and serves as a jumping-off point into this book. This chapter previews the concepts of epidemiology, mentions the importance of crunching numbers, addresses disease prevention, and discusses disease prevention, and more.
Introducing Epidemiology
Epidemiology is the study of human diseases and events. Epidemiologists are disease detectives whose jobs include the following:
Searching for the cause of diseases in humans:
All associations aren’t causal.
Chapter 16
provides concepts on knowing if an association between an exposure and a disease is causal or not.
Identifying people who are at risk:
Certain host factors are associated with diseases. Descriptive epidemiology (see
Chapter 7
) deals with person, place, and time factors that are associated with diseases.
Chapter 5
addresses the risk of people in getting different types of diseases.
Determining how to control or stop the spread:
Knowing the chain of disease transmission helps you prevent or control the spread of a disease. Refer to
Chapter 5
for more information about chain of disease transmission.
Preventing the disease from happening again:
Chapter 11
explains the different levels of disease prevention with practical examples.
Recognizing How Numbers Can Help Study Disease
Epidemiology and biostatistics are like cousin sisters. However, epidemiology isn’t learning about math. I often ask my students whether they like math, and most of the time, they respond no and sometimes emphatically that they hate math. That’s okay. Epidemiology doesn’t deal with hard-core math problems. These sections explain that epidemiologists use a basic knowledge of algebra to calculate numbers.
Grappling with the epidemiologic triangle
The concept of the epidemiologic triangle includes these three factors of a disease:
Agent:
The causative factor (such as a bacteria, virus, or parasite). In other words, the what that causes the disease.
Host:
Humans and non-human animals can harbor a disease. They’re called
disease hosts.
Environment:
Factors in the environment such as temperature (hot or cold), noise, moisture, dusts, and others cause diseases. Also, agents and hosts both live in the environment, which makes a balance between disease and health.
When germs enter and grow in the human body, it’s called an infection. The germs may be bacteria, viruses, parasites, yeasts, fungi, or other microorganisms. They’re agents for an infectious disease. These agents live and multiply in the environment that humans live. But an infection doesn’t necessarily lead to a disease. The favorable conditions in the environment help agents grow.
On the other hand, when a person’s immune system is strong enough, it can fight the germs and cure an infection without causing a disease. If immunity is low, the germ gets the upper hand, and the person fails to resist the infection, which in turn leads to a disease. In a chronic disease model, as I describe in Chapter 6, you can find that the causes are multifactorial — they are called risk factors, instead of agents. Chapter 16 explains the concept of multiple risk factors for a noncommunicable disease.
Classifying epidemiology
Two broad classifications of epidemiology that you need to know are as follows:
Descriptive:
Descriptive epidemiology
provides you answers for what, when, where, and who questions. Most health surveys, censuses, and case reports are descriptive in nature. In descriptive studies, you can identify risk groups or
hot spots
(or areas where diseases and agents cluster). Descriptive information can be highly valuable in generating a hypothesis and conducting a future study to evaluate the hypothesis through experimental studies, interventional studies, or a randomized controlled clinical trial (RCT) (you can find details in
Chapter 17
).
Analytical:
Analytical epidemiology
deals with the why and how questions. Some statistical tests (called inferential statistics) are used for answering these questions. Analytical epidemiology is used to prove the hypothesis.
Understanding epidemiologic transition
The changing nature of diseases is a continuous process, and it depends on several factors including the ecology, public health measures, vaccine development, antibiotic use, genetics, and other host factors. The transition of disease occurrence from acute and infectious diseases to chronic and noncommunicable diseases (NCDs) is called the epidemiologic transition.Chapter 8 describes in greater detail this changing pattern of diseases.
Consider the following: The worldwide pandemic of Covid-19 has evolved as one of the most fatal diseases in human history. Similarly, a few other pandemics including plague, influenza (flu), smallpox, and HIV/AIDS have caused devastations and killed a large number of people. Some other infectious diseases such as pneumonia, diarrhea, malaria, and tuberculosis are still common causes of morbidity and mortality in many developing countries.
On the other hand, noncommunicable diseases such as heart disease, cancer, stroke, unintentional injuries, chronic obstructive pulmonary disease (COPD), Alzheimer’s disease, and diabetes are the leading causes of death in the United States. Developed countries have curtailed mortality rates from infectious diseases. Some of the infectious disease has been eliminated (such as smallpox) in the world or reduced to a minimum level (such as polio, tetanus, measles) in developed countries. Polio is expected to be eliminated soon.
Connecting demography and disease
Changes in demography are certainly affecting the disease pattern and the healthcare costs. Health consequences of aging are many, including pain and arthritis, osteoporosis, falls and accidents, hearing defects, eye problems, heart disease, diabetes, depression, Alzheimer’s, and senile dementia.
The burden of healthcare costs is also escalating. For example, in recent years, one-fifth of older Americans spent more than $2,000 out of pocket on healthcare. Chapter 9 looks at different demographics, including a comparative picture of the population structure of several countries, a list of the ten most populous states in the United States, and the top ten countries with the largest proportion of senior citizens. In addition, you can discover how to project step by step the future population of several countries.
Figuring out rates and risks
One of the focuses of descriptive epidemiology is to calculate rates and risks. Epidemiologists summarize health reports and describe the risks based on numbers. Chapter 10 explains how to calculate important rates such as crude birth rate, crude death rate, age-specific rates such as infant mortality rate, neonatal mortality rate, post-neonatal mortality rate, and perinatal mortality rate, cause-specific rates such as cancer- and heart-diseases mortality rate, and gender-specific rates such as breast cancer rates and prostate cancer rates.
Some of the rates, such as mortality rates, often need to be standardized to compare with similar rates of an entire country or another nation — this process is called standardization. This same chapter shows you how to standardize mortality rates by using direct and indirect methods.
Focusing on Prevention Rather Than a Cure
The three levels of disease prevention include
Averting a disease before it attacks you
Detecting a disease early enough so that you can reduce the disease severity
Preventing disabilities and promoting quality of life
The following sections discuss the specifics.
Identifying prevention levels
Three levels of prevention include primary, secondary, and tertiary prevention. By a simple method of hand washing you can prevent a number of diseases, such as waterborne diseases and Covid-19. Chapter 11 discusses what diseases can be prevented and what the levels of prevention are.
Using vaccines
Vaccines give you a type of immunity which lasts long, sometimes life-long (such as measles) — this is called artificially acquired immunity — in contrast to natural active immunity acquired from exposure to a disease. Chapter 12 explains the importance of vaccines and provides a vaccination schedule by age-group. I also explain what vaccines you shouldn’t get if you’re pregnant.
Surveilling disease
The National Notifiable Disease Surveillance System (NNDSS) is currently surveilling about 120 diseases. The primary purpose of disease surveillance is to predict, detect, and minimize harm caused by an outbreak, epidemic, or pandemic of diseases, and to inform people about possible preventive measures from a future epidemic. Chapter 13 is about methods of conducting disease surveillance.
Studying an outbreak
Some diseases occur in low numbers in a community at any given time. These diseases are called endemic, such as sore throat, ear infection, skin disease, urinary infection, and others. Some diseases can appear suddenly in a large number beyond the normal limit. The diseases are called epidemics; when epidemics occur in small scale or in a confined area, it’s called an outbreak.
Chapter 14 gives you step-by-step methods about conducting an outbreak investigation. I describe my real-life example of investigating an epidemic of blood dysentery (also called shigellosis) in rural Bangladesh. I explain how to prepare your team, how to establish the existence of an outbreak, how to find the sources and the cause of the epidemic, and how to properly collect and analyze data to develop a hypothesis and suggest further studies to prove the hypothesis.
Relying on screening
A number of valid and reliable screening tests are available to detect diseases from apparently healthy individuals. Here are some characteristics of a good screening test:
Safety:
Almost all screening tests are safe and don’t have any side effects. Screening tests also don’t increase risks to individual’s health.
Convenience:
Some screening tests are comparatively more convenient than others. For example, a urine test for glucose is more convenient than a blood glucose test.
Acceptability:
The screening test must be acceptable to the general people.
Sensitivity:
Sensitivity is measured by the proportion of true disease-positive individuals who test positive by the screening test.
Specificity:
This is measured by the proportion of true disease-negative individuals who are tested negative by the screening test.
Predictive values:
The two kinds of predictive values are positive predictive value and negative predictive value. They measure the quality of a screening test.
Through screening tests, you can detect a disease before clinical symptoms appear. Chapter 15 discusses some commonly used screening programs, including mammogram, breast self-exam, Pap test, colonoscopy, PSA for prostate, occult blood test for stool, and more.
Delving into Study Finding
Here I provide snapshots of topics related to studies in this book:
Finding criteria of causal association:
Bradford Hill developed several criteria by which you can determine if an association is causal or not (see
Chapter 16
).
Using different types of epidemiologic studies:
Epidemiologic studies are two types: descriptive and analytical or experimental. Several epidemiological studies fall under these two groups (refer to
Chapter 17
).
Tackling bias and confounding:
Factors like bias and confounding affect study results. These factors must be controlled at different stages of a study (see
Chapter 18
).
Examining ethical procedures in research:
People rely on the findings of a scientific research. You need to follow proper ethical procedures when conducting a study so that the research findings are valid and reliable. (
Chapter 19
discusses ethics in greater detail.)
Figuring Out What You Know about Epidemiology: Some Q&As
How much do you really know about epidemiology? Are you taking an epidemiology course with plans to work in public health, or are you just interested in what causes diseases? No matter, work through these questions to see how much you know about epidemiology.
Before you read a certain chapter, read the corresponding question (I include ten questions for ten different chapters) and try to answer the question. After you read that chapter, you can flip back here and check your answers.
What does epidemiology help you do? (
Chapter 2
)
Epidemiology helps in measuring health status.
Epidemiology deals with disease prevention.
Epidemiology looks for the cause of a disease.
All of the above
Who is considered the Father of Medicine? (
Chapter 3
)
Hippocrates
Joseph Goldberger
John Snow
James Lind
Noah Webster
Who investigated the famous cholera epidemic in London’s Golden Square? (
Chapter 4
)
Hippocrates
Joseph Goldberger
John Snow
James Lind
Noah Webster
In case of infectious diseases, the capacity of an agent in causing a disease is called what? (
Chapter 5
)
Infectivity
Pathogenicity
Virulence
Climate change and global warming can increase the risk of what? (
Chapter 6
)
Waterborne disease
Airborne disease
Parasitic disease
Vector-borne disease
All of the above
Rotavirus is most common among children of what age? (
Chapter 7
)
Younger than 2 years old
Between 2 and 12 years old
Adolescents
What is the top cause of deaths in the United States? (
Chapter 8
)
Heart disease
Stroke
Cancer
Pneumonia
Covid-19
Which country has the largest proportion of senior citizens? (
Chapter 9
)
United States
United Kingdom
France
Sweden
Japan
True or false: Infant mortality rate (death rate in children younger than 1) is one of the best indicators of health of a nation. (
Chapter 10
)
By using a screening test (such as colonoscopy) you can early detect colon cancer. What kind of disease prevention can a screening test offer? (
Chapter 11
)
Primary prevention
Secondary prevention
Tertiary prevention
Answers: 1.) D, 2.) A, 3.) C, 4.) B, 5.) E, 6.) A, 7.) A, 8.) E, 9.) True, 10.) B
VIRUSES CAUSING OBESITY: IS IT REAL?
Obesity in the United States has reached epidemic proportions with a steady rise in prevalence rates over the last 20 years. This epidemic however isn’t limited to the United States — worldwide obesity has nearly tripled since 1975. In 2022, more than 1 billion people worldwide are obese — of them, 650 million are adults, 340 million adolescent, and 39 million children.
The causes of obesity are multifactorial. Although obesity is primarily thought of as a condition brought on by lifestyle choices, recent evidence has made researchers start to look at whether a link between obesity and viral infections in humans exists.
Numerous animal models have documented an increased body weight and a number of physiological changes, including increased insulin sensitivity, increased glucose uptake, and decreased leptin (a hormone that inhibits food intake and increases energy expenditure) secretion that contribute to an increased body fat. Of several viruses, adenovirus-36 (Ad-36) infection is more commonly found an obesity-causing agent in animals. Other viral agents associated with increasing obesity in animals include canine distemper virus (CDV), rous-associated virus 7 (RAV-7), scrapie, Borna disease virus (BDV), SMAM-1, and other adenoviruses.
Some of these mechanistic theories were proven by experimental studies in animals, which are outlined here:
CDV infection causes damage to the hypothalamus, which regulates a person’s energy intake. Damage to the hypothalamus disrupts the carefully coordinated balance between energy intake and expenditure, often leading to increased calorie intake and/or decreased calorie burning, and thereby to rapid weight gain.The thyroid hormones are important for regulating weight. RAV-7 infection causes lymphoblastic infiltration in the thyroid, leading to an underactive thyroid. Hypothyroidism (an underactive thyroid) is a known cause of slower metabolism and weight gain.Scrapie infection causes damage to the adrenal gland, hypothalamus, and pituitary gland. All these factors combined cause weight gain.BDV infection also causes damage to the hypothalamus.In an experimental study, chickens infected with SMAM-1 had 50 percent more abdominal fat than control chickens.Although Ad-36 is a virus that largely infects humans, it’s the first human virus that has been found to cause obesity in animal models. Ad-36 infection was found to increase the amount of adipose tissue. Leptin expression and secretion in adipocytes was observed to be lower and glucose uptake was increased. Both of these effects can be attributed to the development of obesity. Two epidemiologic studies found such an association between Ad-36 and obesity in humans.Further epidemiologic studies and possibly experimental studies are needed to establish whether a causal link exists between obesity and virus infection. However, a virus infection could be one of the many factors that cause obesity. Each of the many factors that cause a disease is called a component cause.
Chapter 2
Epidemiology 101 — Understanding the Basics
IN THIS CHAPTER
Describing the scope of epidemiology
Comparing infectious and communicable diseases
Identifying sources of epidemiologic data
From your classwork, you probably know epidemiology is a core component of public health. Here I want to make sure you have a strong foundation about your coursework in epidemiology.
Chapter 1 gives you an overview to this book whereas this chapter addresses what to expect from your studies in Epidemiology 101 and beyond, focusing on how the field of epidemiology is applied in epidemic control and in disease prevention. This chapter also provides you what you need to know if you plan to work in this field, including what’s necessary for conducting research.
Defining Epidemiology — What to Expect from Your Coursework and Beyond
Epidemiology is what epidemiologists do. And what’s that specifically? They’re scientists who study diseases and events in humans. As an epidemiologist, you’re considered a disease detective in the world of public health. In other words, an epidemiologist searches to identify and measure a disease, its risk factors, and what caused it.
If you dissect the term, epi means upon, demos means people, and logy is the knowledge or education. Therefore, epidemiology is the science of diseases or events that happen in humans.
Like any other investigators at the scene of a crime, epidemiologists begin by looking for clues. As an epidemiologist, you’ll work as a fact-finder. Epidemiology helps you to design studies, conduct systematic methods of investigations, gather data, interview people, create spot maps, and use several other procedures. By studying epidemiology, you not only understand concepts but also get the know-how and their applications in real-life situations.
The following sections deal with descriptive epidemiology, which describes data distribution in terms of time, place, and person and analytical epidemiology, also called experimental epidemiology, to find out the determining factors of diseases.
Describing distribution
When you’re trying to get information about a disease, a few questions come to mind:
What happens?
When does it happen?
Where does it happen?
You get these what, when, and where answers by analyzing information or data about a disease. This type of analysis is called descriptive epidemiology. Suppose you’re hearing about a new disease called mpox (formerly called monkeypox) that occurred in humans in 2022. Descriptive epidemiology answers the following questions:
What is mpox?
What are the symptoms of mpox?
Who is affected by mpox?
When did mpox appear in humans?
Where was mpox found first?
Which U.S. states have the most cases of mpox?
How many people are affected by mpox?
How many people have died from mpox?
What lab methods are used to diagnose mpox?
What is the treatment for mpox?
Descriptive epidemiology refers to describing the characteristics of the disease, the people at risk, morbidity and mortality from the disease, the locations, and the time-trend of the disease. In descriptive studies, you use some statistical tools that are called descriptive statistics.Chapter 7 discusses descriptive epidemiology in greater detail.
Determining determinants
After you know answers to the questions in the preceding section, you can further compare the transmissibility or infectiousness, pathogenicity (whether the agent can cause a disease), and virulence (disease severity and mortality) of mpox with other similar diseases and conduct experimental studies (such as using a vaccine) in controlling the disease. The type of epidemiologic analysis that deals with this kind of in-depth study is called finding determinants of a disease. Refer to Chapter 17 where I discuss different epidemiological studies such as case-control study and cohort study. These types of analytical studies and clinical trials or experimental studies are appropriate for knowing why a disease occurs and how to control it.
Avoiding errors when conducting an epidemiological study
To be successful in conducting an epidemiologic study, even if it’s a small-scale survey for your classwork, be aware of some common mistakes that you can avoid:
Know the population.
All sciences make mistakes, and epidemiology is no exception. The most common mistake is to start a study without knowing the population well. Hippocrates, the Father of Medicine, mentioned in his treatise on
Airs, Waters, and Places
that whenever you enter a new place, know the population characteristics and their mode of life.
Describe when, where, and what.
Don’t forget to provide the context and definitions of your study population. Define when, where, and what — the time frame of your study, the geographical area, and the type of study design. Also, describe how you get your samples.
Make comparisons.
Some types of studies (such as interventions or experimental studies) need a comparison group. Even a historical control is useful when you evaluate the effect of some interventions. However, for descriptive studies, such as a cross-sectional study, you may not bother about having a comparison group.
Chapter 17
discusses the different types of epidemiologic studies.
Estimate causality.
As an epidemiologist, you should be very cautious in calling an associated factor causal.
Chapter 16
discusses Bradford Hill’s criteria of causality.
Calculate sample size.
Inadequate sample size fails to produce valid results.
Recognize generalizability.
Recognize the limitations in your study. For example, if you only study Mississippians, you may not always be able to generalize your findings to the entire United States.
Realizing Why Epidemiology Is Important
Epidemiology is one of the basic sciences of public health that affects almost everyone’s life. This section helps you understand how epidemiology contributes to important issues affecting people’s health.
Here I give you highlights of some important contributions of epidemiology that have impacted human health and survival, such as measuring health status, discovering vaccines and preventing diseases, using epidemiologic methods for identifying a causal association, and suggesting methods for controlling epidemics.
Identifying and measuring health status
John Graunt, an English statistician, was the first person who birthed the concept of vital statistics in London in 1603. He systematically recorded all deaths in London and published his data in the Bill of Mortality — the first book on counting numbers and measuring health status. His initial work has developed the field of vital statistics that is a backbone of measuring health status.
Focusing on disease prevention
The primary objective of public health is to control and prevent diseases that are prevailing in the world. Refer to the section, “Preventing diseases before they hit,” later in this chapter for specifics about what an epidemiologist does.
With present-day scientific knowledge, scientists are still struggling to prevent cancers, heart disease, diabetes, and many disability-causing chronic illnesses. The discovery and uses of vaccines for common infectious diseases have decreased childhood mortality and increased life expectancy of people. These vaccine-preventable diseases include chickenpox, diphtheria, flu, hepatitis A, hepatitis B, Hib, HPV infection, measles, meningitis, mumps, polio, pneumococcal pneumonia, rotavirus, rubella, tetanus, and whooping cough. Epidemiology is continuously looking for vaccines for controlling many more diseases (for example, dengue, Ebola, and malaria).
Searching for causes
As an epidemiology student, you’ll find it fascinating how scientists discovered the causes of diseases. In older days when the actual cause of a disease was unknown, people believed in supernatural forces such as witchcraft, sorcery, and evil spirits causing diseases. Then came the miasma theory — the belief where a noxious form of bad air entering the body caused diseases. That was 20 years before the development of the microscope and a few years before the birth of the germ theory!
You need to be familiar with the germ theory that revolutionized the causal theory of infections. In fact, the germ theory of disease is the currently accepted scientific theory for many diseases. Chapters 3 and 4 discuss the different scientists and discoveries.
In addition to causes of infectious diseases, you should also know the development of the concept of “risk factors” for noninfectious diseases. In 1950, Richard Doll and Austin Bradford Hill suggested that the risk of lung cancer was related to the number of cigarettes a person smoked per day. The famous longitudinal study known as the Framingham Heart Study is another milestone that you need to be aware of because of its far-reaching impacts in public health.
Controlling epidemics
Some people tend to link epidemiology with epidemic control. Epidemic control is just one of many important tasks that epidemiologists do. The Centers for Disease Control and Prevention (CDC) play a pivotal role in controlling the introduction and spread of infectious diseases, providing consultation and assistance to other nations and agencies in improving their disease prevention and the control and health promotion activities, and advocating for vaccination and other disease control activities.
In 1958, the CDC sent a team of Epidemic Intelligence Service (EIS) officers to Southeast Asia for the control of smallpox and cholera epidemics. In 1980, smallpox was eradicated from the world. In 1988, the World Health Organization (WHO), together with Rotary International, UNICEF, and the CDC passed the Global Polio Eradication Initiative (GPEI), with a revised target to end polio by 2026.
Epidemiologists help in controlling disease. As an epidemiology student, you’ll know what diseases have been controlled because of the introduction of vaccines (refer to Chapter 12).
Currently, the WHO recommends the limited use of a malaria vaccine for children living in Sub-Saharan Africa and other regions where Plasmodium falciparum (a severe type of malaria parasite) is highly prevalent. Chapter 12 describes vaccine-preventable diseases and vaccines that are needed for travelers.
Understanding How Epidemiology Tools Are Applied
You should expand your skills by applying epidemiologic tools in community-based research in the following ways:
Apply epidemiologic research designs based on the outcome measurements (see
Chapter 17
).
Measure rates such as incidence, prevalence, odds ratio, relative risk, and others depending on the types of the data (see
Chapters 10
and
17
).
Apply screening methods, depending on the disease conditions (refer to
Chapter 11
).
Investigate an epidemic (check out
Chapter 14
).
Project future populations and control future health problems (see
Chapter 9
).
These sections focus on the role of epidemiology in identifying risks, measuring disease morbidity and mortality, identifying the impact of experimental studies, and in preventing diseases.
Using epidemiologic methods to identify risks
One of the major tasks of epidemiologists is to identify any risk factors for disease, injury, and death. An epidemiologist describes a disease in terms of person, place, and time to identify specific populations (age, sex, race, and occupation) who are at risk and the places (rural or urban, type of housing, environmental conditions, and others) where the public health problems are greater and the time when the disease reaches a peak. Furthermore, epidemiologists measure potential biological, chemical, physical, and behavioral exposures for diseases to identify risk factors. Refer to Chapter 7 for more details.
Measuring morbidity and mortality
Epidemiologists monitor diseases and other health-related events over time. If you monitor a disease in a locality over time, you can describe the level of the cases (morbidity) and deaths (mortality) from the disease. A proper monitoring system can identify when an epidemic is impending before it hits. Based on the rates of morbidity and mortality of the prevailing diseases in your community, you can prioritize the top diseases of public health importance and allocate resources accordingly. Chapter 8 deals with the assessment of disease patterns.
Describing the impact of an intervention
Experimental studies and community-based interventions are part of epidemiologic studies. Here are a few examples of what epidemiological studies have shown:
A low dose of aspirin can reduce the risk for a second heart attack and certain types of strokes, mainly by preventing blood clots from forming within blood vessels.
Supplementation of low-dose iron in low-income postpartum women is effective in reducing anemia.
Different Covid-19 vaccines are effective in reducing hospitalization, ICU admission, and death in fully vaccinated populations.
The scope of epidemiological research is wide — from descriptive studies, analytical studies, and experimental studies. Chapter 17 deals with different types of epidemiologic studies such as an ecological study, a cross-sectional study, a case-control study, and a cohort study.
Preventing diseases before they hit
Epidemiology plays a vital role in all levels of disease prevention. When studying prevention, you need to be familiar with these three pillars of disease prevention (refer to Chapter 11):
Primary prevention:
It refers to preventing a disease from happening. Examples include
Giving vaccines for diseases such as measles, polio, tetanus, diphtheria, whooping cough, and others
Hand washing, social distancing, and using face masks to prevent Covid-19 and many other communicable diseases such as Ebola, influenza, and tuberculosis
Providing safe water and sanitation for the control of diarrheal diseases
Secondary prevention:
This refers to reducing the duration of a disease and preventing complications and deaths. Screening is such a tool used in epidemiology for early detection of diseases. Examples include
Regular self-exams and mammograms to detect breast cancer
A Pap smear test to detect cervical cancer
Tertiary prevention:
This refers to preventing disabilities of people who have suffered from major diseases and injuries. Tertiary prevention also aims to provide people with a quality of life, through new job placement or rehabilitation, depending on the disabilities the person might have suffered. Examples of tertiary prevention include
Rehab program after cardiac bypass surgery
Chronic disease management program (such as for diabetes complications)
Support group sessions for improving coping skills from a major episode of depression
Furthermore, several types of epidemiological studies are effective in predicting risk factors and controlling diseases. Ecological studies, case-control studies, and population-based longitudinal studies are examples of epidemiological studies that have established the role of identifying risk factors and taking measures in the prevention of diseases. For example, epidemiological studies have been used in identifying and determining the risk factors for mental health outcomes such as suicide and suicidal behaviors.
Investigating epidemics of unknown cause
By conducting a continuous scrutiny or vigilance of diseases, you can identify when a new disease has appeared in your locality. A recent outbreak of mpox is a perfect example. Scientists have started learning about the risk factors and mode of transmission of the disease. After a disease appears in the form of an epidemic, the epidemiologists are who’s called to investigate the epidemic.
Here’s what an epidemic investigation team does in a thorough investigation (Chapter 14 describes them in greater detail):
Establishes the existence of an epidemic.
Epidemic investigation starts when a large number of cases are reported. Based on the clinical observations and laboratory results, epidemiologists come up with a case definition of the probable cause of the epidemic. They conduct further investigations to establish the existence, route of transmission, and the disease agent for the epidemic.
Describes the type of the epidemic.
The two types are
Common source:
A disease like watery diarrhea is spread from a contaminated water source such as a river or a pond.
Propagated source:
In this case, the disease (such as blood dysentery) is spread from one infected person to another.
Describes the risk factors in terms of person, place, and time.
Your initial descriptive data analysis helps in developing a hypothesis. You’ll conduct further studies to prove the hypothesis — the latter studies are analytical epidemiologic studies.
Finds out sources.
In this difficult step, you’ll collect environmental samples that you had suspected as possible sources of the agent. Sometimes isolating the disease pathogen from the environmental samples, such as water, is difficult.
Looks for the cause.
This step of an epidemic investigation is important. You gather all the clues such as symptoms of patients, onset of the disease, the nature of the epidemic curve, and the pathogen (bacteria or virus) to establish the cause of the epidemic.
Identifies the modes of transmission.
From the case history, the nature of the epidemic curve, and the source, you can find the mode of transmission: person-to-person spread or a common source spread of the disease.
Intensifies the surveillance system to find new cases.
New case-finding and contact tracing are a few techniques of the surveillance system. By door-to-door search, you can find out new and ongoing cases.
Takes measures for controlling the disease.
Control measures include the treatment of cases, the prevention of the further spread of the disease from the primary cases (the first few cases), and health education such as proper hand washing, sanitation, and others.
Evaluating public health programs
Quality assurance and quality control activities are key components of epidemiologic research. While evaluating public health programs, you’ll measure quality assurance and quality control in every step of the program. In essence, this evaluation ensures validity (or accuracy) and reliability (or precision and reproducibility) of the public health program.
Quality assurance
The purpose of quality assurance activities before data collection is to standardize the procedures and thus prevent or at least minimize systematic or random errors in collecting and analyzing data. The activities involved in this process include the following:
A detailed protocol preparation
The development of data collection instruments
The development of operation manuals
The training and certification of staff
The design of quality assurance activities should follow pretesting and pilot studies.
One of the tools of data collection is a well-designed questionnaire. As a program evaluator, you’ll ensure the program uses a data collection instrument that’s valid and reliable. Choose data collection instruments and procedures that have been used effectively in previous studies to measure both suspected risk factors and disease outcomes. On occasion, even though the questionnaire is a well-established data collection instrument, you may need to pre-test it and validate it in another country population because the characteristics of the two populations may be different. For further information, read Chapter 17.
Quality control
Activities of quality control generally begin after data collection and data processing starts. However, monitoring the data collection process may also ensure quality data. As an epidemiologist, you should follow certain standard quality control strategies:
Observe the procedures performed by staff members.
Identify obvious protocol deviations.
Carry out special studies of validity and reliability in samples of subjects at specified intervals throughout data collection. These procedures include
Periodic checking of the equipment
Field monitoring the use of the instrument
Checking for missing data
