South-East Asia Regional Conference on Epidemiology

Epidemiology in action: past, present
and future
David L. Heymann
In the mid-19th century, epidemiology was instrumental in elucidating the causation of cholera. During
the time of the 1854 cholera outbreak in Soho, London, there were two hypotheses. William Farr, a
registrar in the census office, who is regarded as one of the founders of medical statistics, believed
that cholera was caused by ‘miasma’, or poisonous vapour, coming from the open drains of London.
Miasma was the dominant theory of disease at the time, until it was later superseded by the germ
theory of disease, which emerged in 1861. Meanwhile, John Snow, a leading anaesthesiologist who
administered chlorofom to Queen Victoria during childbirth, was a sceptic of the miasma theory and
believed that cholera was associated with the local drinking-water, which was pumped from the River
Thames. These two great men continuously debated the causation of cholera during much of the mid-
19th century. Finally, it was John Snow, who is considered to be one of the fathers of epidemiology
because of his work in tracing the source of this cholera outbreak, showed that epidemiology is really
an evidence-based science. By talking to local residents, he identified the source of the outbreak
as a public water pump on a Soho street. His studies convinced the council to disable the pump by
removing the handle. He later drew a map showing how the cases of cholera were concentrated near
the water pump, and conducted subsequent studies tracing how sewage-tainted water from the Thames
was being delivered to homes. His work is considered seminal to the science of epidemiology – and by
many to be the landmark event. He was an evidence-based epidemiologist who not only understood
why cholera was occurring but also acted to stop it. Epidemiology in action indeed!
John Snow was not the first to work in public health. In 1796, Edward Jenner developed the
smallpox vaccination technique taking pus from cowpox blisters on the hand of a milkmaid who
caught the disease from a cow named Blossom, after theorizing that the related but less virulent
cowpox infection might explain why milkmaids didn’t get smallpox. He inoculated his gardener’s son
with the cowpox pus, and then did the same to a few other people, and proved that they were immune
to smallpox. Vaccination for smallpox spread around the world and became a common practice by
the end of the 19th century. Mass vaccination was very effective in industrialized countries, where
smallpox incidence was reduced to minimal levels by 1914, but it was still a significant burden in
many countries in the southern hemisphere because vaccine was not reaching people there. It was a
problem of access, which continues even today for many health-related goods.
In 1967, many countries still had smallpox. It was at this time that Dr Bill Foege, a missionary
doctor working in Nigeria, developed a new evidence-based epidemiological strategy of search and
containment. Although he was not the first to propose it, he provided convincing evidence of how
successful it could be in field conditions. It involved searching for all cases of smallpox—smallpox
was always clinically apparent in an infected person—and isolating that person and vaccinating the
person’s contacts or potential contacts in a ring around where that person was living. The strategy was