Biology Reference
In-Depth Information
At about the same time, Daniel Bernoulli (1700-1782) published a
mathematical model developed to assess the effect of cowpox
inoculation on the spread of smallpox. This work is one of the earliest
known scientific efforts to create a quantitative model for assessing the
effects of treatment.
B. What is an Epidemic?
Infectious diseases are a fact of life, and ever since humans began to live
in large groups, epidemics of infectious diseases have left their mark
on human history. To define the term, an epidemic occurs when the
number of infected individuals in the population increases as time goes
by. This definition, however, does not at all convey the human tragedy it
entails.
At No. 39 Broadwick Street in the Soho district of London, there is a pub
named in honor of a physician, John Snow. A plaque on the wall of that
establishment reads, ''The Red Granite kerbstone marks the site of the
historic BROAD STREET PUMP associated with Dr. John Snow's
discovery in 1854 that cholera is conveyed by water.'' John Snow was a
pioneer in the science we now call epidemiology, the study of health and
disease in human populations.
In August of 1854, an outbreak of cholera occurred in London. In the
period between August 30 and September 9, hundreds of people were
stricken and died. John Snow observed that the cases were concentrated
in the vicinity of the Broad Street water pump, and he convinced the
local government officials to remove the handle from the pump, which
they did on September 8. By this time, the peak of the epidemic had
already passed (see Table 2-1).
Dr. Snow's action might have seemed irrelevant but for an independent
investigation by Rev. Henry Whitehead, a local clergyman. Rev.
Whitehead discovered that an infant living at No. 40 Broad Street had
been stricken with diarrhea on August 29 and died on September 2. The
wash water from the baby's dirty diapers had been dumped in the
cesspool at the front of the house, just a few feet from the water pump.
At the clergyman's urging, the cesspool was inspected and found to be
leaking, contaminating the water from the pump. Further, since the
infant's father was stricken with cholera on September 8, John Snow's
actions likely prevented a second epidemic caused by drinking water
from the Broad Street pump. Snow continued his investigations into the
cause of cholera outbreaks and published, in 1855, On the Mode of
Communication of Cholera, linking cholera to the consumption of water
contaminated with fecal matter.
Contaminated drinking water is just one means by which infectious
agents are transmitted. Some, such as the smallpox virus, may be
