This is the map produced by Dr. John Snow during the
1854 outbreak of cholera along London's East End. By mapping all
of the households where cases of cholera occurred, as well asthe pumps
from which the population drew water for their daily lives, Snow was able
to ascertain that the public pump on Broad Street was contaminated with
raw sewage and was thus the reservoir for infection. When the city
removed the pump handle so it could not be used, the epidemic subsided.
This was the first use of descriptive epidemiology,
the deliberate gathering of relevant information concerning the impacted
population (age, sex, race, diet, socioeconomic status, chain of transmission,
etc.) in the attempt to track the specific root cause of disease, as well
as the first reported or index case.
involves a thorough investigation of the disease, including data from descriptive
studies to determine the etiological agent, its mode of transmission and
potential methods of prevention. These studies are often introspective
since they follow a disease outbreak and require examination of infected
versus uninfected populations to determine the root causes, predisposing
factors and possible routes of disease transmission.
involves hypothesis testing to determine the cause of disease or methods
of treating diseases that are already known. Koch's Postulates can
be applied to this type of study when the agent is microbial or modified
if the agent is viral or a fastidious intracellular parasite.