Vibrio cholerae, better known as the silent killer
In 1854, a major epidemic struck London that would kill hundreds of residents in a short span of time. The disease was better known as cholera, and was not new to London since an outbreak had happened in 1831. Cholera, also known as Vibrio cholerae, is transmitted through water.
Cholera can cause:
· Diarrhea – Early on will be fecal, but afterwards painless, massive "rice water stool" which contributes to large amounts of fluid loss
· Vomiting – Also contributes to mass amounts of fluid loss
· Dehydration – With diarrhea and vomiting combined these two movements lead to dehydration. Over 1/5 of a person's entire body weight can be lost in a single day.
· Death – If the body's water and electrolytes are not replenished rapidly within 12 hours, death may occur due to severe dehydration.
Although cholera stunned many continents in the 1800's the immediate cause was unknown at the time. It was believed that cholera was transmitted through the air, but its cause was not known due to the lack of research done on the disease. Dr. John Snow would become known as the "Father of Modern Epidemiology for his hard work and research on the cholera epidemics that struck London in 1831 and 1854.

In 1831, John Snow was the age of eighteen and worked as an apprentice for Dr. Hardcastle when London experienced its first tasting of the cholera disease. Snow was sent to treat patients, who were mostly coal miners, but there was not much he could do to help them. The epidemic ended as soon as it started in 1832, and Snow continued to work on his M.D. degree for the next sixteen years.
Theories explaining the cause of cholera
The "Miasma" theory was believed by many doctors to be the explanation of the spread of cholera and many other diseases in the nineteenth century. The theory stressed eradication of disease through the preventive approach of cleansing and scouring, rather than through the purer scientific approach of microbiology. Dr. William Farr was very supportive of this theory and reasoned that soil at low elevations, especially near the banks of the River Thames, contained much organic matter, which produces miasmata. The concentration of such deadly miasmata would be greater at lower elevations than in communities in the surrounding hills. Dr. Farr produced a graph to support his theory (as shown in Figure 1). Dr. Farr believed firmly in his theory until Dr. Snow's research was published, then his mind would be changed.

Figure 1 - The death rates for cholera seem to relate to the Miasma theory, but later on Dr. Farr's findings would be mere coincidence because the theory would be proved wrong later on.

The second theory was that of spontaneous generation of disease within the blood called the blood generation theory. This theory was essentially chemical, and as such, denied contagion. The most active supporter of the theory was the German chemist Justus von Liebig who held strong views on "fermentation" of the blood. The blood generation theory received negligible support in England.
The "Germ" Theory, which was supported by John Snow, theorized that cholera was caused by a germ cell. Snow did not know the exact germ cell that caused cholera, but believed that the germ was transmitted from person to person through contaminated drinking water. Many other peers, but especially Dr. John Simon (head medical officer of London), deemed Snow's theory peculiar.

Cholera Outbreak starting in 1848
Dr. Snow was thirty-five and another outbreak of cholera had surfaced in London. Snow had been waiting for another outbreak of cholera to happen, and would be tracking its every step. The first victim of the outbreak had been a merchant seaman who was stopping in London for a break and rented a room in the city. The seaman developed symptoms of cholera and died shortly thereafter. Snow's germ theory was supported when he learned that a second gentleman had rented the same room where the seaman died.
Snow believed that the room was not thoroughly cleaned and the germs remained in the room, possibly in the bed linen. As more and more patients were examined, Snow noticed many of them were complaining of digestive problems, which would mean that the germ had to be ingested. These finding proved the Miasma theory to be weak, because if the theory were true, the patients would be complaining about their lungs or nasal passages hurting and not their digestive systems.
In the summer of 1849, the second year of the recent cholera outbreak, Snow decided to share what he considered convincing evidence that cholera was being spread through contaminated water. With his own money, Snow published a pamphlet entitled On the Mode of Communication of Cholera, which was a thirty-nine page pamphlet explaining his evidence to support his theory. Snow provided many examples to explain that if the cholera disease was to be eliminated, drinking water was going to have to be isolated from sewage water. To avoid criticisms by other physicians, Snow did not elaborate that this germ was a living organism. He wrote that this was a poison that had the ability to multiply itself within the digestive tracts of its victims before it was spread to new future casualties.
When cholera broke out the following summer, Snow suspected a contaminated pipe coming from the Thames River was causing the spread of cholera. After looking through the municipal records, Dr. Snow found that two private water companies were supplying water into the district where Snow had lived.
The Grand Experiment
Lambeth Water Company and Southwark and Vauxhall Water Company were two water companies supplying the water for Snow's district. The Southwark and Vauxhall Water Company, was drawing water from an area along the Thames that was known to be polluted by sewage, whereas the other company, the Lambeth Water Company, had recently moved its intake facilities to a location above the sewer outlets. Snow compared the two sources of water with the mortality rates of consumers and came up with some hard evidence. The Lambeth Water Company had changed its intake from opposite Hungerford Market to Thames Ditton [boiling Wells], thus obtaining a supply of water quite free from the sewage of London.
Even though Lambeth moved to a much cleaner intake structure, Vauxhall stayed with the same water intake structure that was present during every occurrence of cholera. Both water companies had many of the same consumers, which meant even though Lambeth had a much cleaner process; residents in the districts were still likely to get a cholera-infected water mixed in from the Southwark and Vauxhall Water Company. Although it was a good idea for Lambeth to change their water intake, it made no difference since the water pipes would intertwine within the district. However, the people supplied by mostly Lambeth seemed to have a fewer death rate as shown in Table 1.

Table 1 – Compares the two water companies with the mortality rate within the district.
In 1852, The Metropolitan Water Act was passed into law, mandating that water companies move their intakes upriver where the water is fresher. Because the Lambeth Company had earlier made the decision to move its intake 22 miles upriver, they became in 1852 the first water company to comply with the new law. Southwark and Vauxhall had yet to comply with the act, therefore was still supplying contaminated water. It wasn't until 1855 when Southwark and Vauxhall were forced to move their water intakes far up the river, and build four new reservoirs to supply fresh water to London. If this move was more strictly enforced when the Act was passed in 1852, it is likely that cholera would not of returned in 1854.
The Broad Street Pump
From house to house Dr. Snow compared the deaths of each household to what water supply they were using at the time. Snow came up with a 71:5 ratio of deaths occurring from Southwark (and Vauxhall) to those deaths occurring from the water that Lambeth Water Company had supplied. Although Snow's critics were not impressed by his results he believed he had obtained "very strong evidence of the powerful influence which the drinking water containing the sewage of a town exerts on the spread of cholera when that disease is present." His critics still believed miasmas caused the disease, and the Thames River is so big, the germ would simply dilute within the mass amounts of water. Since Snow was the first person to make use of a survey of the incidence and distribution of an epidemic in an effort to determine its cause, his evidence was seen as novel and unsound.
In August of 1853, cholera was just a five-minute walk from Snow's doorstep. The disease spread so fast, by the time Snow had heard of its presence nearby, most of the deaths had already occurred. On the evening of September 3rd, snow took a sample of the water from the Broad Street pump (where most of the deaths had occurred). Snow had thought Broad Street was supplied with a clean source of water. To make comparisons, Snow retrieved water from four nearby pumps in Warwick Street, Bridle Lane, Vigo Street, and Marlborough Street and found no visible difference to the water he had pumped from Broad Street. The following day, Snow took the water to a nearby microbiologist for testing, but nothing of significant value had appeared.
Dr. Snow gathered all the information he could find on where people had died, and where they had lived and started to compile a map of his findings. As portrayed in Figure 2, a part of Snow's map would be shown to the Board of Guardians, as he would then suggest for the Broad Street pump handle be removed. As a precautionary measure the Board decided to have the pump handle removed, but were not persuaded by his argument. The Board still believed in the miasma theory and began to spread lime on Broad Street. After the removal of the pump handle and the spreading of the lime, the outbreak had ended.

Figure 2 – Map displaying deaths from Cholera, where most happened near the Broad Street Pump.

After the pump was removed and the outbreak had stopped, Snow did some investigating on his own. John Snow narrowed down Broad Street to be a major distributor of cholera, but was curious as to why so many other deaths occurred so far away. He found that drink shops would use the water from Broad Street to mix in their drinks, and also learned that other people seemed biased to where they pumped their water from even if they were a few miles away from Broad Street. A nearby prison with 535 inmates only had five deaths, which puzzled many miasmists thinking that the airborne disease would pass quickly through the prison. Snow later found out the prison had its own water pump for drinking. The Lion Brewery suffered no casualties due to cholera, which also sent the miasmists in a mix. Snow learned that the workers at the brewery only drank beer, and not water. Snow urged the Board of Health inspectors to examine the brick lining of the well to be sure no sewage could have leaked into the drinking water. No damage was found to the lining.
40 Broad Street
In November, Snow was asked to join a committee of the St. James Parish to investigate the causes of the outbreak by Reverend Henry Whitehead. Whitehead did not believe Snow's theories, but admired is hard work etiquette. Snow published his second edition of On the Mode of Communication of Cholera, which was given to all the members of the Parish. Even though Snow had no physical evidence that cholera was transmitted through the water, Whitehead was surprised with the array of facts Snow had collaborated. He still did not agree with Snow, but was as eager as Snow to find the cause of cholera. While Whitehead was reviewing reports by the Registrar General about cholera deaths from the week ending September 3, 1854 he came across an intriguing event.
Whitehead read that an infant died of severe dehydration after having symptoms of cholera on September 2nd. Whitehead realized that this infant was the first death of cholera during this outbreak. The infant's house was located right in front of the house, which was addressed 40 Broad Street. Whitehead went to the child's mother at 40 Broad Street and asked basic questions of her death. The mother had stated that when her baby was sick, she had cleaned the child's diapers in a pail, and then emptied the pail into the drain about a cesspool in front of her house. The cesspool was within a few feet from the Broad Street pump (shown in Figure 3). On April 23rd, after being advised by Whitehead, inspectors did finally find that the lining for the pump well had decayed. It was not found in the previous two times because the soil outside the well had not been examined, and no one knew a cesspool was within feet from the water pump.

Figure 3 – Displayed is the Broad Street pump and the Cistern that are feet from each other, causing contamination in the drinking water on Broad Street.

Once the child died, no more feces were being expelled into the drinking water, causing the epidemic to end. Whitehead and Snow, and the Parish Committee presented a report to the General Board of Health. The board dismissed the conclusion. Snow died of a stroke on June 16, 1858, still gaining no ground with his theory on the spreading of cholera.
Was Snow's Theory Valid?
Fillipo Pacini, an Italian anatomist performed autopsies on people killed of cholera. He examined the intestinal walls of the victims and discovered a comma-shaped bacillus, which he described as a Vibrio. Snow was proved to be correct with the help of Robert Koch, a German microbiologist. Koch rediscovered, isolated, and cultured the cholera bacillus, Vibrio cholerae.
For his hard work, persistence, and strong efforts to find the cause of cholera, Snow was, and still today is known as "The Father of Epidemiology"


UCLA Department of Epidemiology, School of Public Health retrieved on March 10, 2006, from,
BIO 118: Cholera, retrieved on March 11, 2006 from,

Cholera 8.3 of 10 on the basis of 4175 Review.