How Data Became One of the Most Powerful Tools to Fight an Epidemic

The River Lea originates in the suburbs north of London, winding its way southward until it reaches the city’s East End, where it empties into the Thames near Greenwich and the Isle of Dogs. In the early 1700s, the river was connected to a network of canals that supported the growing dockyards and industrial plants in the area. By the next century, the Lea had become one of the most polluted waterways in all of Britain, deployed to flush out what used to be called the city’s “stink industries.”

In June 1866, a laborer named Hedges was living with his wife on the edge of the Lea, in a neighborhood called Bromley-by-Bow. Almost nothing is known today about Hedges and his wife other than the sad facts of their demise: On June 27 of that year, both of them died of cholera.

The deaths were not in themselves notable. Cholera had haunted London since its arrival in 1832, with waves of epidemics that could kill thousands in a matter of weeks. While the disease was on the decline in recent years, a handful of cholera deaths had been reported in the preceding weeks, and it was not unheard-of for two people sharing a home to die of the disease on the same day.

But the deaths of Mr. and Mrs. Hedges turned out to be the start of a much bigger outbreak. Within a few weeks, the working-class neighborhoods surrounding the Lea were suffering one of the worst cholera epidemics in London’s history. The newspapers delivered the same sort of morbid accounting that has obsessed us all in the age of the SARS-CoV-2 coronavirus: the terrifying upward trajectory of runaway growth. Twenty cholera deaths were reported in the East End the week ending July 14. The following week’s tally was 308. By August, the weekly death toll had reached almost a thousand. London had not experienced a major outbreak of cholera for 12 years. But by the second week of August, the evidence was unmistakable: The city was under siege.

Then, as now, the first line of defense was data. Londoners were able to track the march of cholera across the East End in close to real time, thanks primarily to the work of one man: a doctor and statistician named William Farr. For most of the Victorian era, Farr oversaw the collection of public-health statistics in England and Wales. You could say without exaggeration that the news environment that surrounds us now is one that William Farr invented: a world where the latest numbers tracking the spread of a virus — how many intubations today? What’s the growth rate in hospitalizations? — have become the single most important data stream available, rendering the old metrics of stock tickers or political polls mere afterthoughts.

In 1866, Farr had become a convert to a theory of cholera first proposed by the London doctor John Snow more than a decade before — the idea, which turned out to be true, that the disease was being transmitted in drinking water. And so as the deaths began to mount in the East End, Farr immediately began investigating the water sources in the neighborhood.