Of all the different types of science, epidemiology is one of my favorites. However, I find that many people do not know what epidemiology is, what it is that epidemiologists do, and why it is important. Thus, what follows is a brief examination of the science of epidemiology, a public health science. This brief will describe the primary objectives of epidemiologists, some interesting subdisciplines of the epidemiology, and the important, yet frequently taken for granted ways epidemiology affects our everyday lives.
What Is Epidemiology And What Do Epidemiologists Do?
The exact meaning of epidemiology has been a moving target. It has evolved from being defined simply as the study of diseases in specific populations, to the study of states of health-disease distribution and determinants, including exposures, susceptibility and resistance in a population, and the application of this knowledge in ways that result in improvements to populations’ health and well-being. Epidemiological research is focused on the manifestation of diseases in specific populations rather than on the individual. This is a process predicated on the idea that morbidity is not arbitrarily distributed among communities, but related to specific physiological and/or environmental attributes, which make people susceptible to, or protected against certain diseases. Thus, in order to better understand the characteristics that lead to, or protect against disease, epidemiologists generally are focused on achieving five overarching objectives: understanding the cause, the burden or distribution, and the natural history of disease, the evaluation of treatments and therapies, and the development of effective public health policies and practices.
A vital aspect of epidemiology is the cautious evaluation of data collected in scientific studies. The ability of epidemiologists to shrewdly assess the literature is vital because public health programs and policies are developed based on the evidence gathered from these studies. Consequently, the ability to effectively quantify research findings is especially important. Accordingly, a high degree of rigor is required when identifying cases in epidemiological studies (at least in theory), and acutely specified research objectives and standards of measurement are the norm.
Conversely, it is also true that epidemiologists are frequently constrained in their capability to investigate, much less conclusively determine the pathogenesis of disease, which requires essential measurements that can be distant from the mechanisms. Likewise, in epidemiologic research, the ability to make causal inferences based on discoveries of associations is usually tenuous, largely due to the type of study designs most frequently available.
How Does Epidemiology Relate To Public Health?
You can think of epidemiology as the cornerstone of public health. It is the study of the manifestation, distribution, and determinants of health in a population, while public health is the application or strategic implementation and administration of health and well-being related knowledge in the form of public initiatives aimed at preserving, and hopefully improving people’s health. Thus, epidemiologists are focused on understanding the processes and conditions associated with the occurrence, and when applicable, the transmission of diseases. Public health advocates focus on the epidemiologist.
Although public health is based on the knowledge reaped from scientific investigations, much of the work done by those in the field of public health involves public policy. Consequently, the funding, planning, and administration of public health programs are deeply affected by politics. Public health professionals are tasked with persuading government officials, the medical community, business interests, and the general public of the value in investing in public health, which improves social conditions and increases economic productivity. Over the last two hundred years, there have been many examples of the convergence of public health, policy and politics. Some notable examples include the American sanitarian movement in the 19th century, public housing, the wars on both HIV/AIDS and cancer, and most recently the enactment, (attempted) repeal, and replacement of the Patient Protection and Affordable Care Act (often called Obama care).
While there are many ways that epidemiology exerts an important influence on public health, it is not the only field of science that provides us with vital public health knowledge. Indeed, both public health and epidemiology are influenced by many disciplines, from medicine, demography, and biology, to a broad assortment of other social, life, and physical sciences. Moreover, epidemiology incorporates knowledge, data, empirical and cultural referents, reasoning, methods, techniques, and levels of analysis from several branches of knowledge. This includes pathology, toxicology, internal medicine, pediatrics, and various math and social science disciplines, like engineering, economics, and sociology.
These diverse fields address issues pertinent to public health, offering important insights that guide public-health activities. For instance, when epidemiologists are attempting to ascertain the extent of occurrence and the natural history of diseases, patient histories and case studies are precious sources of data fielded from the medical sciences, like internal medicine. Pathology and toxicology are also important resources. Engineering and economics play an important role in helping public health officials to develop efficacious interventions. Finally, the clinical sciences offer many insights that result in better disease diagnosis and treatment. A prominent example of the contributions of the clinical sciences to epidemiology is a Morbidity and Mortality Weekly Report on five cases of Pneumocystis carinii pneumonia (PCP) in Los Angeles at the start of the 1980s.
Every week the Centers for Disease Control and Prevention (CDC) publishes the Morbidity and Mortality Weekly Report (MMWR), an epidemiological digest for the United States. The MMWR contains public health information and recommendations derived from state health departments across the country. On June 5, 1981, MMWR published a report of five cases of Pneumocystis carinii pneumonia (PCP) among young men in Los Angeles. Physician and immunologist M.S. Gottlieb, H.M. Schanker, MD, and a small group of other clinical scientists authored the report.
In late 1980, four otherwise healthy young men contracted PCP, among other opportunistic viral infections. These cases were highly unusual because up to that point PCP was exclusively limited to severely immunosuppressed patients, typically occurring in individuals receiving chemotherapy for cancer or immunosuppressive agents to prevent rejection of a trans- planted organ. However, none of these men were exposed to these predisposing risk factors, lacking a clinically apparent underlying immunodeficiency. However, the clinicians did report that all of the men were described as “homosexuals”, and two of them had died by the time the report was published. In an editorial note that accompanied the June 5, 1981, MMWR report, CDC officials stated that noted that early clues suggested the disease was acquired through sexual contact.
This seminal report was soon followed by a MMWR, Vol. 30, no. 25, on July 3, 1981, Kaposi's Sarcoma and Pneumocystis Pneumonia Among Homosexual Men — New York City and California. More than fifty physicians serving patients in New York City, Los Angeles, and the San Francisco Bay area contributed to this report. The report indicated that over the course of 30 months, 26 incidence of Kaposi's sarcoma (KS) had been diagnosed in homosexual men. Like with PCP, these incidence of KS where startled and garnered the attention of clinical scientists because at the time, reports of KS were rare in the U.S., with an estimated annual incidence between 0.02-0.06 per 100,000. Moreover, patients usually treated for KS were most often in their 60s or older, and the mean survival time was 8 to 13 year. The 26 cases in the July report occurred in men between the ages of 26 and 51, and 8 of the 26 patients died within 24 months after KS was diagnosed.
In an effort to ascertain what this new disease was the CDC established a task force of diverse experts, which included cancer epidemiologists, parasitology, virology, immunology, and medical scientists specializing in sexually transmitted diseases. Within 18 months of the first MMWR on PCP, all major risk factors for acquired immnodeficiency syndrome, and preventative recommendations had been published.
Improving Living Conditions and Saving Lives
British physician and epidemiologist, Thomas McKeown and colleagues have made the argument that to date, the aggregation of disease related knowledge and promotion of public health programs have been more beneficial to people’s health outcomes than the development of biomedicines. In his groundbreaking 1976 book, The Role of Medicine, Mckeown argues that economic growth, rising living standards, and improved nutrition are the primary sources of most historical improvements in the health of developed nations. Other prominent researchers including John McKinlay and Sonja M. McKinlay (1977) also furthered the argument that medical care is largely unrelated to improvements in the health of populations.
In 1994 medical researchers Bunker, and Frazier, Mosteller found that since the turn of the 20th century, the US life expectancy had increased by 30 years. Moreover, they presented convincing evidence suggesting that while advancements in bio-medical technologies have been a boon to the health and well-being of people, most of the gains in life expectancy are due to public health advancements. To be exact, 5 years of this increase are the result of medical advancements; 25 years are due to progress in public health campaigns. Nevertheless, As a consequence of public health initiatives promoting the wide use of biomedicines, particularly vaccines that protect against infectious diseases are routine.
One of the most important factors in gains in life expectancy in the last 100 years was the establishment of basic sanitation measures. The strict segregation of human waste from clean water, and food safety regulations have contributed to significant decreases in foodborne and waterborne microbial contamination that commonly result in the outbreak of intestinal diseases, including typhoid fever, cholera, and dysentery. Likewise, the legislation of automobile and occupational health and safety laws, and increased access to maternal planning and contraceptives are also notable examples of epidemiologic research based public health initiatives that have drastically reduced morbidity and mortalities.
The examples listed above demonstrate the efficacy of public health, while further elucidating the diversity of disciplines that influence public health action. Similarly, public health advocacy is engaged by a diverse group of actors. Institutions, organizations, as well as individuals, have affected the previously mentioned list of public health successes. Three major sources of public health activism are academic institutions, political institutions and civic organizations.
Social Epidemiology
Epidemiology has a long-standing relationship with sociology, which includes the adaptation of deeply rooted ways of thinking inherited from its tradition. The study of social relationships and health was one of the first areas to bring together the fields of sociology and health, particularly the field of scientific research on "social support”, which emerged in the 1970s. Recently, there has been even greater utilization of the scientific principles and methodologies of sociology. This increased interest is due to the realization that individual behavior, as well as the material realities of a person’s life, outside the realm of strictly physiological mechanisms can exert a powerful influence on health outcomes.
Epidemiologic studies of the social determinants of health and well-being are becoming more common. Research into the social determinants of health focus on a myriad of areas, including socio-economic status, culturally specific behavioral norms, social support, housing conditions, government legislation, and availability of or access to a wide range of social resources like education and peoples’ ability to participate in political processes. Many social epidemiologic studies elucidate disparities in the quality of education, employment opportunities and income. Likewise, there are many studies exploring what effect being residentially segregation into neighborhoods where poverty is highly concentrated has on peoples’ health and well-being. Also, there are an increasing number of epidemiologic studies investigating the health effects of enduring discrimination in numerous interpersonal contexts; particularly, gender, ethnic, religious and sexually based prejudice.
To date, the data indicates that all of the aforementioned areas are detrimental to people’s health. These issues are the focus of social epidemiology. Social epidemiology is an outgrowth of research from numerous academic disciplines that elucidated the uneven burden of disease endured by certain groups. These discrepancies in health outcomes are not due to luck, nor solely a consequence of inadequate access to quality health care, but arise at the pernicious intersection of deeply embedded discrimination, inequitable economic order, and deleterious government policies and programs, which can lead to unintended and often harmful consequences. Social epidemiology is predicated on the idea that in order to improve people's health and well-being, actionable strategies that address disparities in the conditions in which people are born, grow, live, work and age must be implemented.
While social epidemiology is still a branch of the epidemiology in its infancy, I am confident that it will increase in importance as we glean a greater understanding of the social production of disease. As we gain more knowledge in the field, we also have an increased responsibility to mitigate inequalities that negatively impact peoples’ quality of life.