Science of Water : Concepts and Applications

290 The Science of Water: Concepts and Applications
√ Note: You don’t need to be a rocket scientist to fi gure out just how deadly cholera was during
the London cholera outbreak of 1854. Comparing the state of “medicine” at that time to ours
is like comparing the speed potential of a horse and buggy to a state-of-the-art NASCAR race
car today. Simply stated, cholera was the classic epidemic disease of the nineteenth century, as
the plague had been for the fourteenth. Its defeat was a refl ection of both common sense and
of progress in medical knowledge—and of the enduring changes in European and American
social thought.
How does a person contract cholera? Good question. Again, we refer to the CDC for our answer.
A person may contract cholera (even today) by drinking water or eating food contaminated with the
cholera bacterium. In an epidemic, the source of the contamination is usually feces of an infected
person. The disease can spread rapidly in areas with inadequate treatment of sewage and drinking
water. Disaster areas often pose special risks. The aftermath of Hurricane Katrina, for example, in
New Orleans caused concern for a potential cholera problem.
Cholera bacterium also lives in brackish river and coastal waters. Shellfi sh eaten raw have been
a source of cholera, and a few people in the United States have contracted cholera after eating raw
shellfi sh from the Gulf of Mexico. The disease is not likely to spread directly from one person
to another; therefore, casual contact with an infected person is not a risk for transmission of the
disease.
Flashback to 1854 London
The information provided in the preceding section was updated and provided by the CDC in 1996.
Basically, for our purposes, the CDC confi rms the fact that cholera is a waterborne disease. Today,
we know quite a lot about cholera and its transmission, how to prevent infection, and how to treat it.
But what did they know about cholera in the 1850s? Not much—however, one thing is certain: They
knew cholera was a deadly killer. That was just about all they knew—until Dr. John Snow proved
his theory. Recall that Snow theorized that cholera is a contagious disease caused by a poison that
reproduces in the human body and is found in the vomitus and stools of cholera victims. He also
believed that the main means of transmission was water contaminated with this poison.
Dr. Snow’s theory was correct, of course, as we know today. The question is, how did he prove
his theory correct? The answer to this provides us with an account of one of the all-time legendary
quests for answers in epidemiological research—and an interesting story.
Dr. Snow proved his theory in 1854, during yet another severe cholera epidemic in London.
Although ignorant of the concept of bacteria carried in water, Snow traced an outbreak of cholera to
a water pump located at an intersection of Cambridge and Broad Street (London).
How did he isolate this source to this particular pump? He accomplished this by mapping the
location of deaths from cholera. His map indicated that the majority of the deaths occurred within
250 yards of that water pump. The water pump was used regularly by most of the area residents.
Those who did not use the pump remained healthy. Suspecting the Broad Street pump as the plague’s
source, Snow had the water pump handle removed and ended the cholera epidemic.
Sounds like a rather simple solution, doesn’t it? For us, it is simple, but remember, in that
era, aspirin had not yet been formulated—to say nothing of other medical miracles we take for
granted—for example, antibiotics. Dr. John Snow, by the methodical process of elimination and
linkage (Sherlock Holmes would have been impressed—and he was), proved his point, his theory.
Specifi cally, through painstaking documentation of cholera cases and correlation of the comparative
incidence of cholera among subscribers to the city’s two water companies, Snow showed that
cholera occurred much more frequently in customers of the water company that drew its water from
the lower Thames, where the river had become contaminated with London sewage. The other company
obtained water from the upper Thames. Snow tracked and pinpointed the Broad Street pump’s
water source. You guessed it: the contaminated lower Thames, of course.