By Sara L. Merwin, MPH with Amanda Merwin Lewis, MPH

For many years, during and after my studies in public health, I have had to explain what an epidemiologist is and does.  Epi what?  I was asked.   What does that mean? Do you study skin?  (No, that’s the epidermis).  From the Greek root, epi is on, demos is people, logo is study.   Epidemiology therefore is the study of “what befalls a population”.  (We say “epi” for short since the whole word can be troublesome to pronounce and spell.)

Epidemiologists in the news

Enter the coronavirus and there is the flowering of understanding about the role of the epidemiologist.   At least for anyone watching or reading the news.

Finally! The epidemiologist is the new hero and the term has entered into the popular vernacular.  Epidemiology is a core discipline of public health and it is concerned with the distribution of health related conditions in the population.

What do epidemiologists do anyway?

Epidemiologists design studies in a systematic fashion, use statistical methods to separate “truth” from supposition, estimate burden of morbidity (sickness) and mortality (death), evaluate effectiveness of drugs and medical devices, examine risks for diseases, injuries and psychosocial conditions, conduct surveillance and biomonitoring and use a combination of the above plus other key postulates and principles to distinguish between causality and association.

When I want to be glib, I say that we epidemiologists count and sort sick people.  That is, we tally up conditions, risks, and outcomes and put them into neat little buckets.   Classification and taxonomy play a huge role. 

In all seriousness, anyone who has had formal training in epidemiology is likely to be a qualified professional; the programs of study are laborious and full of drudgery.  No one becomes an epidemiologist for the money or the star appeal.   This in contrast to some of the charlatan self-appointed experts making pronouncements without basis in reality or evidence.

Types of epidemiology

The discipline of epidemiology has many branches: the methods used in chronic disease epidemiology subsume many non “disease” type conditions: injuries, occupational, psychological manifestations, social determinants of health, cancers, in addition to what are commonly understood as chronic disease states: diabetes, heart disease, etc. etc.   Molecular and genomic epi are other specialized fields of study.   

Another type of epidemiology — that of infectious diseases – is way sexier than chronic disease epi.   Outbreak investigation is the stuff of apocalyptic novels and Hollywood movies. (Also the stuff of daily life circa Spring 2020.)   When is the last time you saw a movie or made-for-tv special with A-list stars studying highway collisions?  Less sexy, but often in the news, are investigations of food borne illnesses; a recent bacterial contamination of romaine lettuce comes to mind.  Locating the source of an infectious illness — whether it’s the egg salad at the church picnic or a plague such as ebola or COVID-19 —- is the key to understanding where and why it occurred and to prevent spread or future incidents.  The study of disease distribution has been around since ancient times, but the landmark investigation that established the modern era of epidemiology was made in London in 1854 by Dr. John Snow, who traced the origin of a cholera outbreak to a water pump.   

Naturally there is overlap between infectious disease and chronic disease epi methodology: we do count and sort measles cases, but we also study the manner in which it spreads.  With the exception of some psychological phenomena, chronic diseases do not spread from person to person. 

Medicine and epidemiology: different but related

In the media we currently see many physician-scientists identified as epidemiologists. This usually means that in addition to earning an MD degree, an MPH, DrPH or PhD is undertaken.  There is a dialectic between clinical medicine and epidemiology.   The physician practitioner is focused on caring for the individual patient, whereas the epidemiologist views the aggregation of persons and conditions to understand how groups of people act or are afflicted; “evidence” is the byword.   And it is distinguished from “anecdotes”.   Evidence is derived from rigorous methods.   Anecdotes are observations, which often provoke an interest to delve deeper to understand clinical occurrences, resulting in investigations that confirm or refute, aka evidence.  Most physicians and other health care professionals rely upon evidence to make informed decisions in rendering care of their patients.  An epidemiologist without a medical degree is qualified to study medical phenomena, make models and predictions of diseases, and advise clinicians, but may not treat patients. In the hospital and public health departments and agencies, nurses are also instrumental members of the epidemiology team in the role of infection control officers.  

New terms we are hearing

As a result of the pandemic, epidemiologists are now seemingly as common as the mailman or plumber,  and a whole new lexicon, previously obscure to the casual observer, has entered into the common parlance.

It seems we are all epidemiologists when we talk about “flattening the curve”. Such has the epi jargon permeated our daily conversation. 

Here we have (in the context of the pandemic):

containment – the earliest effort to obviate the spread of the disease by identifying the source and putting measures in place to isolate infected individuals

mitigation – if containment has failed, the effort to limit the spread of a disease by various means, including social distancing, and closures of schools, businesses and nonessential activities

contact tracing – the process of discovering by whom and to whom a disease is spread

vector – some thing or organism that spreads a disease: mosquitoes spread malaria, humans spread coronavirus via virus-laden droplets, causing covid-19

[Less referred to is fomite, which is an inanimate object that conducts the disease]

transmissibility – a measure of how an infectious disease is passed between people

epidemic curve (aka epi curve) – the distribution of a condition over a defined period of time within a defined population; it is a model represented graphically, and gives rise to the expression to “flatten the curve”, the concept during this outbreak that fewer cases flooding health care facilities all at once will prevent excess sickness and death

case fatality rate – the proportion of deaths due to a disease divided by the number of all cases of the disease within a defined period of time, expressed as a percentage and usually used to describe an outbreak.  It is different than mortality rate, which has softer time parameters.

R0 (R naught) – an estimate of how many others an infected individual passes the infection to; virologists might say “the basic reproduction number of the virus”

The above are in addition to all the medical and operational terms used to describe, treat and prevent the spread of cover: PPE, donning and doffing, ventilators and so on.

Clearly there is much to learn about the COVID-19 and the health professionals who offer predictions and advice.   For better or worse, many of us now have sufficient time, if not mental bandwidth, to absorb new information.   

We don’t know what we don’t know…

For my part, I am relieved to see the importance of my profession elevated and promoted on a daily basis.  Unfortunately, even the wisest and most skilled infectious diseases and epidemiology experts are unable to pinpoint with great accuracy the future trajectory of the coronavirus:   too much about the virus’ behavior is yet unknown, and we can never predict the impact of human behavior (in combination with governmental actions/inactions) or the availability of the necessary medical equipment. 

From the NY Times 18th April, 2020:  “Our knowledge gaps [about coronavirus] are still wide enough to make epidemiologists weep.”

And weep we do, for the catastrophic impact of this plague on so many domains of our lives, here and around the globe. 

However, as we move through the different phases of the pandemic, we DO have experts in science, medicine and epidemiology who can guide us about how to mitigate against the personal risks of acquiring COVID-19 as well as advising those in government who must make difficult decisions about protecting constituents.

About the Author

Author, Speaker, Hospitalization Expert, Researcher

Author and speaker Sara L. Merwin MPH received her Master of Public Health degree in epidemiology from the Columbia Mailman School of Public Health and has worked as a clinical researcher at Northwell Health System and Montefiore Medical Center. She has held faculty appointments at Zucker Hofstra School of Medicine and Albert Einstein College of Medicine. Her career and research focus includes patient and professional education and communication.