10.1B: The Science of Epidemiology - Biology

10.1B: The Science of Epidemiology - Biology

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Epidemiological studies include disease etiology, disease surveillance and screening, biomonitoring, and clinical trials.

Learning Objectives

  • Discuss the various factors that characterize epidemiology

Key Points

  • Epidemiologists rely on other scientific disciplines like biology to better understand disease processes, statistics to make efficient use of the data and draw appropriate conclusions, social sciences to better understand proximate and distal causes, and engineering for exposure assessment.
  • Epidemiologists employ a range of study designs from the observational to experimental. Its study designs are generally categorized as descriptive, analytical, and experimental.
  • The identification of causal relationships between disease exposures and outcomes is an important aspect of epidemiology.

Key Terms

  • epidemiologist: A scientist (often a medical doctor) who specializes in epidemiology.
  • causal: A cause of something; causing.

Major areas of epidemiological study include disease etiology, outbreak investigation, disease surveillance and screening, biomonitoring, and comparisons of treatment effects such as in clinical trials. Epidemiologists rely on other scientific disciplines like biology to better understand disease processes, statistics to make efficient use of the data and draw appropriate conclusions, social sciences to better understand proximate and distal causes, and engineering for exposure assessment.

Epidemiological studies are aimed, where possible, at revealing unbiased relationships between exposures such as alcohol or smoking, biological agents, stress, or chemicals to mortality or morbidity. Epidemiologists employ a range of study designs from the observational to experimental. Its study designs are generally categorized as descriptive, analytical (aiming to further examine known associations or hypothesized relationships), and experimental (a term often equated with clinical or community trials of treatments and other interventions).

In observational studies, nature is allowed to “take its course”, as epidemiologists observe from the sidelines. Observational studies have two components: descriptive or analytical. Descriptive observations pertain to the “who, what, where and when of health-related state occurrence”. On the other hand, analytical observations deal more with the “how” of a health-related event.

Controversially, in experimental studies, the epidemiologist is the one in control of all of the factors relating to the particular case study. Experimental epidemiology contains three case types: randomized control trials (often used for new medicine or drug testing), field trials (conducted on those at a high risk of conducting a disease), and community trials (research on social originating diseases).

The identification of causal relationships between these exposures and outcomes is an important aspect of epidemiology. It is nearly impossible to say with perfect accuracy how even the most simple physical systems behave beyond the immediate future. The complex field of epidemiology, which draws on biology, sociology, mathematics, statistics, anthropology, psychology, and policy only makes analysis even more challenging.

A common theme in much of the epidemiological literature is that “correlation does not imply causation. ” For epidemiologists, the key is in the term inference. Epidemiologists use gathered data and a broad range of biomedical and psychosocial theories in an iterative way to generate or expand theory, to test hypotheses, and to make educated, informed assertions about which relationships are causal, and about exactly how they are causal.

What Is Epidemiology?

Epidemiology is the branch of medical science that investigates all the factors that determine the presence or absence of diseases and disorders. Epidemiological research helps us to understand how many people have a disease or disorder, if those numbers are changing, and how the disorder affects our society and our economy.

The epidemiology of human communication is a rewarding and challenging field. Much of the data that epidemiologists collect comes from self-report—from answers provided by people participating in a study. For instance, an epidemiological study may collect data on the number of people who answer, “Yes” when asked if someone in their household has trouble hearing. Each person providing such an answer may interpret “trouble hearing” differently. This means that the results of such a study may be quite different from a study in which actual hearing (audiometric) tests are administered to each person in a household.

Also, many epidemiological estimates try to determine how the number of people affected by a disorder changes over time. The definition of a disorder also tends to change over time, however, making estimates more difficult. Even scientists working in the same field at the same time may not agree on the best way to measure or define a particular disorder.

Epidemiology and biology of physical activity and cancer recurrence

Physical activity is emerging from epidemiologic research as a lifestyle factor that may improve survival from colorectal, breast, and prostate cancers. However, there is considerably less evidence relating physical activity to cancer recurrence and the biologic mechanisms underlying this association remain unclear. Cancer patients are surviving longer than ever before, and fear of cancer recurrence is an important concern. Herein, we provide an overview of the current epidemiologic evidence relating physical activity to cancer recurrence. We review the biologic mechanisms most commonly researched in the context of physical activity and cancer outcomes, and, using the example of colorectal cancer, we explore hypothesized mechanisms through which physical activity might intervene in the colorectal recurrence pathway. Our review highlights the importance of considering pre-diagnosis and post-diagnosis activity, as well as cancer stage and timing of recurrence, in epidemiologic studies. In addition, more epidemiologic research is needed with cancer recurrence as a consistently defined outcome studied separately from survival. Future mechanistic research using randomized controlled trials, specifically those demonstrating the exercise responsiveness of hypothesized mechanisms in early stages of carcinogenesis, are needed to inform recommendations about when to exercise and to anticipate additive or synergistic effects with other preventive behaviors or treatments.

Keywords: Biomechanisms Cancer Exercise Physical activity Recurrence.

Conflict of interest statement

The authors declare that they have no conflicts of interest.


Commonly proposed mechanisms relating physical…

Commonly proposed mechanisms relating physical activity to cancer recurrence and/or survival. Potential additive…

Colorectal cancer serves as a…

Colorectal cancer serves as a useful example for studying physical activity mechanisms because…


In 2016, the NHLBI released its Strategic Vision, which will guide the Institute’s research activities for the coming decade. Many of the objectives and compelling questions identified in the plan focus on factors that account for differences in health among populations. For example, researchers are looking at what factors make individuals or populations resistant or prone to diseases, despite having experienced the same exposures such as diet, smoking, environmental and social factors. Recruiting and retaining researchers interested in epidemiology research and developing a diverse scientific workforce are also high priorities.

Genes and biology may account for some differences in health among different populations. However, a wide range of factors related to lifestyle choices, behaviors, and socioeconomic status may also play a role in causing differences in health. Our research seeks to better understand the causes of health differences and to identify ways to improve public health.

Population studies have entered an exciting period when advances in assay methods, imaging technologies, and electronic data are creating new scientific opportunities. These tools make it possible for large epidemiology studies to explore what makes individuals susceptible to disease. To capitalize on these opportunities, NHLBI established an Advisory Council Working Group on Epidemiology and Population Science, which looked at the current landscape, emerging tools, and future opportunities in population science and made important recommendations that contributed to the Institute’s strategic thinking in this area.

The NHLBI’s large-population cohort studies have been major generators of new knowledge that has informed the molecular basis for disease and identified targets for new treatments. For example, NHLBI research has transformed the way the public approaches cardiovascular disease by conducting numerous studies that focus on diverse populations. The Women’s Health Initiative (WHI) continues to yield new insights that advance our understanding of heart disease and other diseases in women.

It is important that the NHLBI continue to build on its legacy of excellence in population studies research. Our population studies have led to a wide range of discoveries and initiatives that will reduce health disparities and improve health outcomes in heart and vascular diseases, obesity, women’s health, and precision medicine.

What is Epidemiology?

Epidemiology is a branch of medical science concerned with the spread and nature of infection and disease. It examines diseases before it reaches or while it is at epidemic or pandemic stage. Rather than analyzing or studying the structure, evolution and genetics of a disease and the bacteria or virus that causes it - an area of study known as pathology (1) - epidemiology examines how diseases or conditions exist, spread or survive in a given population (2). Epidemiology might look at why a condition is prevalent in one population and not another, and the potential risks of that condition spreading.

Epidemiology is fundamental to understanding how diseases spread (waterborne or airborne). It works alongside pathology and other branches of medical science in understanding why a condition (including contagious diseases, but not exclusively so) is in one geographical area and not another, and what risk factors might lead to it spread. Also, they might seek to understand the cause of why a condition has not spread and appears unlikely to do so. Sometimes, there are geographical or social barriers to disease. Understanding these can be fundamental to preventing the spread of a disease.

When a disease outbreak is identified, an epidemiologist may ask some of the following questions:

  • Why are infection rates of this disease higher than normal?
  • Why are infection rates of this disease higher than normal in this location?
  • What is the potential for the disease to spread?
  • What are the wider implications of it spreading?
  • What are the likely causes of this outbreak, epidemic or pandemic?
  • What treatments are available?
  • What can we do now to slow it down? What are known effective short-term and long-term strategies?

Epidemiology studies rates of infectious diseases, and also those with an environmental cause such as toxic spillage, food based diseases such as food poisoning or water contamination, and localized air and water pollution. Today, it is not solely about infectious diseases, but also about biological, social and environmental causes. Some epidemiologists study instances of domestic violence, addiction or mental illness for example (3), to attempt to understand their causes and effects. This means that other social “diseases” such as suicide rates, substance abuse and other non-disease related conditions are also of interest to some types of epidemiologist. These conditions can be epidemic too, although not with the typical biological causes.

Epidemiology is more about statistical analysis of distribution, looking for patterns, and working out causes of a condition. It is more about examining trends than it is about the medical aspects of a condition, although this does play a part.

Epidemiology and Public Health at CDC

Corresponding author: Stephen B. Thacker, MD, Office of Workplace and Career Development, Office of the Director, CDC, MS E-94, Atlanta, GA 30329. Telephone: 404-498-6010 Fax: 404-498-6365 E-mail: [email protected]

Epidemiology is the study of the distribution and determinants of health-related states or events in specified populations and the application of this study to control health problems ( 1 ). However, in public health, the terms "field epidemiology" ( 2 ) and "applied epidemiology" ( 3 )---which emphasize use of results in public health settings---define the practice of epidemiology at CDC. Epidemiology has been characterized as the basic science of public health ( 2 ), and its practice at CDC has shaped the agency's development and will contribute to its future success.

Epidemiology at CDC

Epidemiology at CDC began with Dr. Alexander Langmuir and his extraordinary contributions to CDC and to public health. Hired in 1949, Langmuir served as first Chief Epidemiologist at CDC and remained in that position until 1970 ( 4 ). In 1952, he convened the first Conference of State and Territorial Epidemiologists, which became the organization representing the approximately 2,500 epidemiologists working today in states. Langmuir defined disease surveillance at CDC ( 5 ), and this model since has become an established global public health practice. In 1961, Langmuir helped bring the MMWR to CDC to disseminate timely public health surveillance data and to communicate the results of public health investigations. He was an international consultant in epidemiology at the Winnipeg flood disaster of 1950 the radiation studies that followed the bombings at Hiroshima and Nagasaki, Japan the global smallpox-eradication program and other international issues of public health importance.

During the 1960s, CDC epidemiologists continued to work in infectious diseases domestically, especially drug-resistance in hospitals and Salmonella in commercial chicken products. A 1961 study of leukemia in Niles, Illinois ( 6 ), marked the first of several investigations of cancer clusters and the introduction of chronic disease epidemiology to CDC. Langmuir extended the scope of CDC epidemiology by initiating a family planning activity in 1963, and 4 years later, he established the Metropolitan Atlanta Congenital Defects Program.

Possibly Langmuir's most recognized contribution was the Epidemic Intelligence Service (EIS), a combined training and service program formed initially in response to the threat of bioterrorism ( 7 ). Since 1951, approximately 2,700 EIS officers have provided CDC and the states with a rapid-response capacity for any public health need in an estimated 10,000 investigations domestically and internationally ( 8 ). EIS-trained epidemiologists remain at CDC in leadership positions others occupy prominent positions in other government agencies, academia, and international organizations.

One investigation put CDC and applied epidemiology in the public eye for the first time. On April 12, 1955 (the anniversary of the death of Franklin Roosevelt), the favorable results of the field trial of inactivated poliovirus vaccine were announced 5 days later, a massive national vaccination campaign was initiated. However, within a week, paralytic polio was diagnosed in a child who had received the vaccine, and as new cases emerged, Langmuir was called on to investigate. A surveillance unit was set up and began issuing daily reports. On May 8, the U.S. Surgeon General declared a moratorium on the program. Using all the EIS officers and working with the states, CDC established the association with two lots of vaccine from one manufacturer, cleared the other four manufacturers, and persuaded public authorities by June 1 to restart the program ( 9 ).

The 1970s saw an expanding role for epidemiology at CDC. CDC epidemiologists identified contaminated bottles of intravenous fluid, leading to a national recall linked liver cancer in certain workers with exposure to vinyl chloride played a pivotal role in the global eradication of smallpox identified Ebola virus in Zaire and the Sudan identified toxic-shock syndrome and uncovered the association between aspirin use and Reye syndrome. The Cancer and Steroid Hormone Study, conducted in collaboration with the National Cancer Institute, and the Study of the Efficacy of Nosocomial Infection Control were important not only for their findings but also for the introduction of large numbers of analytic epidemiologists and statisticians to CDC. The 1976 investigation of Legionnaires disease in Pennsylvania highlighted collaboration between laboratory scientists and epidemiologists in the discovery of new and important pathogens ( 10 ). Field epidemiology training programs established in Canada and Thailand were the first of now 34 EIS-like programs around the world ( 11 ).

Acquired immunodeficiency syndrome dominated the 1980s and, together with expansion of agency programs in noninfectious diseases, added behavioral and social scientists to CDC's team of epidemiologists, statisticians, and laboratory scientists. Infectious diseases---notably Escherichia coli O157:H7 associated with hemorrhagic diarrhea and hemolytic-uremic syndrome---remained important. However, studies of chronic diseases, violence, disasters, refugees, and toxic exposures to both environmental and commercial products such as cooking oil, medications, diet supplements, and paint engaged increasing numbers of epidemiologists.

Since 1990, CDC epidemiologists have collaborated with an expanding array of partners around the world to tackle noninfectious diseases and injuries, as well as emerging infections, such as hantavirus, cryptosporidiosis, West Nile virus, severe acute respiratory syndrome, and the threat of pandemic influenza. Global eradication programs in polio and dracunculiasis (guinea worm disease) engage a global network of epidemiologists with the World Health Organization, international governments, and the private sector. Prevention effectiveness and informatics have been added to the epidemiologist's toolkit. Hundreds of epidemiologists were deployed to address disasters at the World Trade Center and the anthrax poisonings in 2001 and hurricanes Katrina and Rita in 2005.

The Role of the Epidemiologist in the Future

CDC epidemiologists will continue to respond to emergent events, be they newly emerging infections, natural disasters, or terrorism, and will continue to study public health problems, such as unintentional injuries, environmental exposures, cardiovascular disease, obesity, tobacco use, and violence domestically and internationally ( 12 ). Public and private partners on the public health team will expand to include new disciplines. The analytic tools and technologies available will increase, and CDC epidemiologists will maintain a critical role in capacity building. Finally, CDC epidemiologists must maintain the scientific integrity the agency has established by remaining rigorous yet adaptable to the challenges new global realities bring to public health.

Laboratory of Epidemiology & Population Science

The goal of the research conducted in the Laboratory of Epidemiology and Population Science (LEPS) is to identify and test etiologic and predictive hypotheses about health conditions and aging in diverse populations. LEPS builds this science into large population-based studies, with the overall goals to:

a. Study long-term exposures and subclinical disease indicators that increase the susceptibility to loss of cognitive and physical function and subsequent disability.

b. Identify biomarkers and other useful surrogates that are integrated measures of pathology and ‘disease.’

c. Identify life periods when exposures initiate or aggravate pathologies that increase the risk for loss of cognitive and physical function and disability.

d. Identify factors that precipitate crossing thresholds to clinical cognitive or physical disability and determine whether control of these factors decreases the risk for clinical events.

e. Provide data from observational studies and clinical trials for use in translational research in experimental and public health settings.

f. Investigate the biology of health disparities in the context of aging.

g. Disentangle the interaction between socioeconomic status and race in the development of age-associated health disparities.

Tying it all in with human behavior

Scientists have begun to compare sewage samples with census data as a way of tracking different societal behaviors

The Australian government was an early adopter of wastewater-based epidemiology, starting out with a handful of testing sites in 2009 and now with a nationwide drug monitoring program in place. Through sewage samples, this initiative monitors the usage of 13 different substances, including nicotine, cannabis and opioid-based pain relievers, with local trends tracked through the help of chemistry researchers around the country. And some of them harbor grand ambitions for wastewater-based epidemiology.

Philip Choi is a PhD student using mass spectrometry and molecular biology to measure different aspects of population health through human waste. This extends beyond illicit drug use to include things like diet and the use of anti-depressants, making new connections between consumption habits and the lifestyles of the community.

The secret is to tie it all in with census data, which is exactly what Choi and his colleagues did the last time Australia conducted a nationwide census in 2016. The scientists had workers at treatment plants around the country freeze wastewater samples during the week of the census, and then mail them into Choi's lab at the University of Queensland for chemical analysis.

In searching these samples for certain biomarkers and comparing them to the census data, the team carried out the first ever study on the links between wastewater chemicals and social and economic measures of a population.

“Prior to this study, some studies used wastewater-based epidemiology to study exposure to potentially harmful chemicals or pollutants such as pesticides, herbicides, flame retardants and so forth,” Choi tells New Atlas. “However, drug measurement studies made up the bulk of wastewater-based epidemiology studies. Additionally, previous studies measured what people are consuming. Our study is unique in that we show why people might consume different things.”

And the results of the study, published in The Proceedings of the National Academy of Sciences in October, reveal some intriguing insights indeed. For example, the scientists found that the opioid-based pain reliever tramadol was used more heavily in areas where more people work as physical laborers. In areas populated by people with lower levels of education, they found higher use of anti-depressants and lower levels of dietary fiber. Some of these results were more surprising than others.

“Before we analyzed our data, we expected socio-economically advantaged populations to have a better quality of diet, or take less drugs, and so forth,” Choi explains. “What was surprising, however, was that our data was able to show how specific aspects of socioeconomic advantage or disadvantage, such as having no home internet connection, lacking high school education, or having a high skilled occupation, were linked to diet or drug consumption. For example, we did not expect to find that lack of high school education was strongly linked to lower dietary fiber intake and higher consumption of amitriptyline, an antidepressant.”

Higher caffeine and citrus consumption were other examples of habits tied to a strong socioeconomic status that revealed themselves through the wastewater samples. These new relationships that scientists are uncovering between human behavior and the chemicals in their sewage may prove highly valuable in building long-term pictures of population well-being, but could they also have an immediate impact, or even act as a warning sign of impending disaster?


Albert Ko is a professor and chair of epidemiology of microbial diseases at the Yale School of Public Health.

“That’s way too slow,” said George Rutherford, a professor of epidemiology and biostatistics at the University of California at San Francisco School of Medicine.

Albert Ko is professor and department chair, epidemiology of microbial disease, at Yale School of Public Health, and professor of infectious diseases at Yale School of Medicine.

We brought in scores of experts from infectious disease, epidemiology , public health, laboratory medicine, all these different areas to try to help us design and prepare what we think is the most up-to-date information.

In cities across the US—ranging from Boston, Massachusetts in the northeast to Las Vegas, Nevada in the southwest—scientists are working with public health officials to conduct wastewater-based epidemiology .

For an article in the Journal of Public Health and Epidemiology , the author must fork over $650 for “handling.”

Cuse: From a story standpoint, I felt the critical goal in the first part of the show was to focus on the epidemiology .

The epidemiology of polio is simple to understand—as simple as seeing the inevitability of the major crisis we have before us.

That brings us to the usual problem: cancer epidemiology is extremely complex.

Epidemiology of Gestational Weight Gain and Body Weight Changes After Pregnancy.

The work of the modern fathers of epidemiology was consciously based on Hippocrates.

It is in this chapter that the epidemiology comes into closest contact with social and economic history.

Its place is indeed unique among epidemic diseases it is the oldest and most obdurate of all the problems in epidemiology .

He saw that influenza was the crux of epidemiology , and paid special attention to it.

This theory was based upon the geographical distribution and epidemiology of the disease.


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