Contact Tracing is the Key To Solving the Spread of Infectious Diseases

Contact Tracing is the Key To Solving the Spread of Infectious Diseases

The process by which epidemiologists are now shedding light on the spread of SARS-CoV-2 is not new. We can look back on history, back to John Snow and his mapping of the cholera epidemic as the first life-saving example of contact tracing.
Today it is COVID-19 that is causing panic around the world, but in 19th century England, the fear of cholera, a terrible disease, was the cause. It causes such severe diarrhoea that a victim can lose up to ten litres of water in a day. If not treated, it can lead to rapid dehydration and death within a few days. The disease first appeared in Europe in 1831, an unwanted import from the Indian subcontinent, where it was endemic. Within a year, over 50,000 British people died, causing widespread panic. Doctors did not know what to do. They supplied their patients with arsenic and strychnine, they administered tobacco enema, they wrapped them in flannel soaked in turpentine, they bled them with leeches and they blew them with nitric acid. All to no avail, of course. No one knew what caused the disease, but the prevailing opinion was that cholera was somehow transmitted by bad air or a “miasma” emanating from sick people and rubbish. A London dentist claimed that the solution was to fire cannons every hour to disperse the bad air!

Contact Tracing is the Key To Solving the Spread of Infectious Diseases

Dr John Snow, a young apprentice doctor at the time, cared for many of the cholera victims. He did not buy the idea of poisoned air. It seemed clear to him that cholera was due to a poison that acted directly on the intestines and was therefore most likely introduced by mouth. His suspicions turned to water when he discovered that the city of Birmingham had been spared cholera. What was the difference here? Nobody drank river water! The water of the River Tain was so foul that no one could tolerate it. The people of Birmingham drank only well water. By 1849, Snow had published a pamphlet that pointed out that cholera was spread by water, but his ideas were largely ignored. Snow was educated not by education but by training and was not a member of the establishment. His views were belittled. Most prominent doctors did not want their theories of miasms to be disrupted, and in any case the epidemic had subsided by 1849.\

Contact Tracing is the Key To Solving the Spread of Infectious Diseases

In 1854, Snow got a chance to prove his theory. In London, a terrible cholera epidemic broke out in the Soho district, where more than 500 people died within ten days in an area of a few city blocks. Dr Snow then took a map of the city and painstakingly mapped out the location of the houses where someone had contracted cholera. An amazing pattern was revealed. The red dots indicating cholera cases were grouped around a main street then known as Broad Street. What on this street could cause cholera, Snow wondered? He soon found the answer.

A water pump that supplied the neighborhood was located in the exact area marked by the dots on his map as the center of the epidemic. He soon discovered that seven men who lived outside Soho but worked in the area around the pump were all dying of cholera and that a widow who had just moved to Hampstead from the neighbourhood but had sent some of the water she was used to drinking was also dying. But perhaps the most convincing observation Snow made was that in a nearby brewery (where the workers never drank water) not a single worker died of cholera!

At this point Snow turned to city officials, showed them his card and suggested that the handle of the pump in Broad Street be removed for public health reasons. Legend has it that this stopped the epidemic immediately. The fact is that the number of new cholera cases had slowed down by the time the pump handle was removed to a trickle. Snow did not stop the cholera epidemic single-handedly, as the myth suggests, but that does not diminish its power in any way. He clearly showed that cholera can be transmitted by polluted drinking water, and further demonstrated that sewage was the culprit.



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