Cholera: You Know Nothing, John Snow

Aliases: cholera

Cholera moves in lockstep with extreme poverty; the pathogen capitalizes on the frailty of poor infrastructure to spread. Tragically, that means it is incredibly common around the globe. Worldwide, there are an estimated 1.4-4.3 million cases and 28,000-142,000 deaths from the disease each year. Its short incubation period (the time between a person contracting the disease and being able to pass it to someone else) of 2 hours to 5 days means that it can appear to emerge out of nowhere in explosive epidemics. And its effects are devastatingly lethal; if left untreated, cholera can kill within hours.1

Despite how truly terrible it is, cholera has had some positive effects on society. The disease has become iconic in epidemiology, the study of the patterns, causes, and effects of disease, after inspiring the birth of the field. During a major cholera epidemic in London’s Soho neighborhood in 18542, Dr. John Snow (yes, really) painstakingly mapped deaths caused by the disease and documented the household water usage. He personally visited 658 homes to determine their water source3, systematically compiling evidence to support his theory that cholera was water-borne and combat the prevailing “miasma” theory, which suggested that cholera was spread by “bad air” containing particles of decomposed matter.2

Eventually the data became overwhelming (all the deaths had occurred within 250m of one street intersection), and indicated that the source of the cholera was the now infamous Broad Street pump. Snow succeeded in having the handle of the pump removed3, and the epidemic came to a halt. Yet despite the fantastic results, doubts lingered about Snow’s theory. As he himself admitted, without knowing the cause of the disease he couldn’t prove that the removal of the pump handle had stopped disease spread; the epidemic could have been waning anyway for any number of reasons.2 Snow’s work was unpopular with the medical community and his ideas were widely rejected.3 He was only vindicated posthumously, when Robert Koch identified Vibrio cholera (the bacteria that causes cholera) in 1885.2

Education saved John Snow’s groundbreaking work. It was lost to obscurity until the 20th century, when it was revived by WH Frost, the first professor of epidemiology at the Johns Hopkins University School of Hygiene and Public Health. Frost edited a reprint of Snow’s book on cholera in 1936 and proceeded to popularize it in his classes. He used Snow’s efforts to combat cholera as a classic case study of epidemiology in action, and this view spread throughout academic circles globally.4 Today John Snow is acknowledged as one of the fathers of epidemiology, and he and the Broad Street pump have become icons.2,4

cholera
Come at me, bro.

Cause: Cholera is caused by ingesting the bacteria Vibrio cholera in either contaminated food or water. It affects all age groups, afflicting adults and children. When it comes to cholera, humanity may be its own worst enemy; humans are a main reservoir for the disease and global warming (which is at minimum partially our fault) creates favorable environments for the bacteria. But it is our predilection for inequality that may be our greatest gift to the disease; it is especially common in areas of poverty or crisis, where there is generally poor infrastructure.1

Consequence: 80% of cases are asymptomatic. That means that 80% of people who contract cholera experience no ill effects, although they can still potentially infect others. Of those that develop symptoms, 80% have a mild to moderate course of the disease; only 20% are severe cases that can be fatal, experiencing acute watery diarrhea and severe dehydration.1

Cure: Finally some good news: cholera is amazingly responsive to treatment. Up to 80% of cases can be successfully treated simply with rehydration salts and with proper treatment the case fatality rate plummets below 1%. There are also two WHO pre-qualified oral vaccines. But although the disease is treatable, the best protection against cholera is prevention. Safe water and sanitation are critical to long-term control and prevention. That means piped water and treatment plants, water filtration and safe storage in homes, and safe sewage and waste disposal systems. Here’s the rub: this kind of systemic change demands economic development to offset the significant initial investment and high maintenance costs.1

References

  1. Cholera. World Health Organization. July 2015. Web. 17 September 2015.
  1. Kukaswadia, A. John Snow− the first epidemiologist. PLOS Blogs. 11 March 2013. Web. 17 September 2015.
  1. Paneth, N. 2004. Assessing the contributions of John Snow to epidemiology: 150 years after removal of the Broad Street pump handle. Epidemiology, 15: 514-516.
  1. Vandenbroucke, JP, HM Eelkman Rooda, & H Beukers. 1991. Who made John Snow a hero? American Journal of Epidemiology, 133: 967-973.

Image source: https://en.wikipedia.org/wiki/John_Snow_(physician)#/media/File:John_Snow.jpg

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Suzi Claflin

I am a postdoctoral fellow studying chronic disease epidemiology.

2 thoughts on “Cholera: You Know Nothing, John Snow”

  1. Very interesting, Suzi. I’ve heard about cholera all these years and never
    known anything much more about it than it was water borne. Now I know
    quite a lot more! Good work you are doing!

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