A mystery in Victorian London paved the way for the techniques we use to track COVID-19
Shoe leather — that is, getting out and talking to people — helped lead to a critical breakthrough
This column is an instalment in our series Apocalypse Then, in which cultural historian Ainsley Hawthorn examines the issues of COVID-19 through the lens of the past.
After decades of labouring in obscurity, the COVID-19 pandemic has thrust epidemiologists onto the global stage, and their work monitoring, tracing and forecasting the path of the disease is only becoming more critical as variants like delta and lambda emerge and spread.
The strategies epidemiologists use to track disease today, though, are only about 170 years old. They have their roots in a mysterious outbreak in Victorian London.
In 1854, there was an eruption of cholera centred on Golden Square in the Soho district of the city, which, coincidentally, had been the site of a 17th-century plague pit. Cholera is an intestinal infection that causes diarrhea so severe it leads to acute dehydration. Over the course of just 10 days, 500 Londoners died.
At the time, miasma theory was the most popular explanation for cholera and other contagious diseases. The fumes released by waste and decay, it was believed, travelled through the air as poisonous vapours, infecting those who inhaled them.
Nineteenth-century London was a very smelly place. The odour of sewage rising off the Thames River was so putrid, it was known as "the Great Stink." It's easy to see why Londoners might have ascribed their ailments to this conspicuous stench.
Something smelled about that theory
A physician who lived near the square, though, didn't think the pattern of this outbreak was consistent with transmission by toxic vapours, and he set out to uncover the epidemic's true cause.
John Snow was a medical innovator who pioneered the use of ether and chloroform as anesthetics. He had developed a method for calculating safe dosages of these drugs — so physicians could administer enough to knock a patient out without killing them — and had served as personal anesthetist to Queen Victoria during two of her births.
Instead of examining corpses or relying on theory to explain the epidemic, Snow took a different approach.
He went to the affected neighbourhood and started talking to the people who lived there.
As he questioned the relatives of the deceased, Snow noticed that most of the deaths had occurred in a cluster around the intersection of Broad and Cambridge streets.
There were fewer and fewer cases as one moved further away from that intersection. At the corner of Broad and Cambridge stood a public water source, the Broad Street pump.
When Snow inquired after the dead who hadn't lived near the pump, their friends and neighbours confirmed that most of them had worked or attended school in the Broad Street area.
One woman who had died of cholera at Hampstead West End, almost eight kilometres away, had lived in the Golden Square neighbourhood and liked the water from the Broad Street pump so much she had a bottle of it sent up to her in Hampstead every day.
On Sept. 7, only a week after the outbreak had begun, Snow went before the board of guardians of St. James's Parish. Evidence in hand, he convinced the board to have the handle of the pump removed the next day, rendering it unusable.
Almost immediately, cholera cases in the area declined.
Research continued well after threat diminished
Even after the epidemic ended, Snow kept at his research for months to better understand the transmission of the disease. He went to public records offices, tracked down the addresses of all the Londoners who had died of cholera during the outbreak, then plotted them on a map of the city, showing conclusively that the deaths had been concentrated around the pump.
He even determined why two groups of people in the neighbourhood hadn't gotten sick, workers at its local brewery and tenants of its poorhouse.
The poorhouse, it turned out, had its own well where residents fetched their drinking water. The brewers, on the other hand, were given a daily ration of malt liquor and, as far as the brewery owner knew, didn't drink water at all.
As for the source of the contagion, the pump sat not three feet from a leaky cesspool where, it was later discovered, the diapers of an infant stricken with cholera had been washed just before the epidemic began.
Snow published a book about his investigation, On the Mode of Communication of Cholera, which helped to prove that the disease is transmitted through water or food that's been contaminated with human feces.
The book also provided the framework for studying disease that became the foundation of the modern field of epidemiology. Snow demonstrated that, by tracing patients' movements and looking for patterns, illnesses could be tracked back to their sources.
Some 167 years later, Snow's basic techniques are helping health practitioners understand and rein in the COVID-19 pandemic.