Historical Examples of How Epidemiology has Led to Prevention of Disease

Prevention Despite Lack of Biological Knowledge: Historical Examples of How Epidemiology has Led to Prevention of Disease
Paige M. Breedon and Austin A. Mardon

Epidemiology, defined as the study of disease distribution and determinants of health-related states and events in specified populations, is quintessential for public health because it can allow for the prevention of various diseases [1]. Through the use of epidemiological approaches and investigations, one can observe disease trends and associations and act in a timely fashion without knowing the biology or pathogenesis of the disease. Historically, epidemiology has been of utmost importance. For instance, in the past, commonly held theories and knowledge of pathogens, such as germ theory, were not known; however, through keen observation of trends and patterns of human behaviour, catastrophic events were avoided. 

Snow and Cholera
One of the most well-known and impressive examples of epidemiological observations leading to breakthrough realizations and consequential preventative efforts occurred in 19th century England. Dr. John Snow used his medical and scientific experience to understand the cholera outbreaks occurring in England at the time. Ultimately, he proposed a theory about why the disease was occurring that contradicted the previously accepted miasmic theory [2]. Before his investigations, the theory known as the miasmic theory suggested that cholera was due to 'poison in the air' such that malodors were produced from rotting organic matter and were transmitted through the air [2]. It is important to note that germ theory was not known during this time period. Several observations led Snow to reject the Miasma theory and develop a theory that cholera was a water-borne disease despite being blissfully unaware of the pathogenesis of the disease, let alone the knowledge of the existence of Vibrio cholerae bacterium, which is responsible for the disease. Firstly, Snow noted that the disease spread through "human intercourse," meaning the disease travelled from continent to continent via trade routes; the disease came to new locations when a person from an affected area arrived there [2]. He also turned his attention to the local water supply companies, who, after a policy change, were obliged to change water sources and were no longer able to use River Thames by 1855. However, some companies waited longer into the deadline to change, and Snow was able to use this to distinguish individuals getting Thames River water versus individuals getting upstream supplied water [2]. The Lambeth company moved upstream earlier than others and observed that districts that got their water from this company had no deaths from cholera; with these observations, the water-borne theory of cholera was discovered [2]. 

Semmelweis and Handwashing
Another prime example of epidemiology prompting preventative action and thus advertising major catastrophes was Ignaz Semmelweis instituting handwashing in the 1840s to reduce the transmission of childbed fever [3]. Specifically, Semmelweis started work at a university hospital with three obstetric wards; two were of the most importance, one run by medical students and the second division run by midwives. Semmelweis first noted the maternal death rate of 22.5% in November of 1841, where deaths were from 'childbed fever' known today as streptococcal blood poisoning [3]. He observed that the clinic differed because the medical student-run clinic had students attending autopsies of women who died during labour from 'childbed fever' all morning and then proceeding to help women deliver later in the day, and the midwife-run clinic did not perform such procedures. Semmelweis followed his observations with careful experimentation involving enforcing hand washing, which led to a drop in mortality from 11.4% to 3% [3]. He further investigated and found that a corpse was not the only source of 'cadaveric particles,' it could also spread through the air and dirty linen. Finally, Semmelweis demonstrates how a keen eye for observation and study of disease distribution is faster than the complex and complete knowledge of how a disease is transmitted and or causes changes to the human body.

Jenner and Smallpox
Lastly, Edward Jenner, in 1796, also made observations that led to a revolutionary form of primary prevention in medicine known today as vaccination [4]. May 1796 marked when Jenner inoculated a healthy 8-year-old boy named James Phipps with an experimental vaccination of cowpox, intending to protect him against smallpox [4]. The cowpox vaccine came after observing that dairymaids and farmhands were immune to smallpox. Specifically, he experimented by inoculating these individuals with smallpox matter into several incisions and despite this, dairymaids and farmhands did not 'take' the infection [4]. Through these vital observations, Jenner was able to work towards the eradication of smallpox and introduce a new kind of medicine that has substantially evolved and saved many lives ever since.

Epidemiological Observations Today
Today observations continue to allow for preventative action despite incomplete biological knowledge, especially amidst the current COVID-19 pandemic, where much was and remains unknown about the SARS-COV2 virus. Like many other disciplines, epidemiology contributes to making actions based on evidence, i.e. evidence-based medicine. 

Overall, one of the greatest lessons learned through the history of studying disease trends and distribution is that knowing the biological pathogenesis of a disease is not necessary to take preventative action. Through countless examples, one can see the immense impact epidemiology has had on public health and the future of medicine. From dissipating outbreaks to the invention of vaccination, one can see how vital it is to work based on evidence and allow epidemiology to inform such decisions. 

REFERENCES
[1]     Frérot, Lefebvre, A., Aho, S., Callier, P., Astruc, K., & Aho Glélé, L. S. (2018). What is epidemiology? Changing definitions of epidemiology 1978-2017. PloS One, 13(12), e0208442–e0208442. https://doi.org/10.1371/journal.pone.0208442
[2]     McCaffery, K., & Weisberg, R. (2017). John Snow and the Waterborne Spread of Cholera: A Case Study of Scientific Creativity. Journal of Genius and Eminence, 2(1), 1–14.
https://doi.org/10.18536/jge.2017.04.02.01.01
[3]     Newsom, S. (2001). The history of infection control: Semmelweis and handwashing. The British Journal of Infection Control, 2(4), 24–25. https://doi.org/10.1177/175717740100200410
[4]     Rusnock, A. A. (2016). Historical context and the roots of Jenner’s discovery. Human Vaccines
& Immunotherapeutics, 12(8), 2025–2028.
https://doi.org/10.1080/21645515.2016.1158369