It’s been a while, hunh? Well here’s a short post on what I’m reading.

I’m reading The Ghost Map by Steven Johnson, and it concerns the cholera outbreak in the Soho area of London in 1854.

If you’re an epidemiologist, you’ve heard of John Snow and you know about the Broad Street pump. This outbreak and the investigation into its cause is widely regarded as the birth of modern epidemiology.

The story goes something like this. In London in 1854, people got their water not from the tap, but from wells which were accessed by pumps placed in various locations throughout the city. This seemed to work OK. What worked less well is the fact that Londoners of the time basically lived in a big huge pile of shit. Sewers were a new invention and were far from perfected. Emptying into them were various cesspools throughout the city, and the sewers emptied into the Thames making it the most poluted river in history (?).

The pump on Broad Street in Soho (now Broadwick St.) was well known for its sparkling, clear and refreshing water, unlike many other pumps in the city which sound like they were pretty disgusting. But in the late summer of 1854 cholera spread throughout the area around the pump killing 700 people in 10 days. That’s really fast. In those days, the prevailing theory of why cholera spread was that it was spread by really bad smells, which London had lots of (remember all those cesspools, open sewers, and the big polluted river).

But John Snow had looked at cholera outbreaks before, and he theorized that the infection was actually spread through water. To be more precise, it was spread through fecal-oral transmission. Yes that’s right, it you ate or drank someone’s shit (or water that was contaminated with it), and that person just happened to have cholera, then there was a pretty good chance you were going to get it too. And since Londoners basically lived on a big pile of shit (2.5 million people in 30 square miles – that’s almost 100,000 people per square mile – my neighborhood is about 8000 per square mile – just think of all the waste that generates – and remember, NO TOILETS) there was a pretty good chance that someone was going to ingest their neighbor’s feces.

And that’s what gappened around the Broad Street pump. A young infant somehow contracted cholera, and her mother washed her diapers out and threw the water into the house’s cesspool, and that, due to old rotting walls, drained right into the well under Broad Street. 10 days later, 700 had died.

But as I said, John Snow had figured that cholera was spread through the fecal-oral route and this was his chance to prove it. He carefully documented the patterns of deaths in the area, and showed that the vast majority of deaths were in those who drank from the pump. Those who didn’t – even if they lived within yards of it – didn’t. A good example of the latter was the brewery down the road. None of the workers got sick because part of their pay was beer. They never used the pump and so none of them fell ill.

Snow convinced the Town Council (or whatever) to take the handle off the pump, thus rendering it useless. The legend is that the epidemic immediately abated. Now it turns out that the epidemic may have been slowing down for other reasons anyway, but none-the-less this is the first time an epidemiologic investigation lead to a public health intervention.

Snow eventually convinced others of his theory of how cholera spread using this and other evidence. Thus he’s earned fame amongst us as the founding father of epidemiology.

Now you’ve looked at the title, but still have heard nothing about Henry Whitehead. I hadn’t either until I read the book, and he turns out to be interesting. He was a curate in the area and was intimately involved with the people who lived there. He tended to many of the sick as they died. But he’s very interesting because he was clearly a scientist at heart.

After the outbreak, he wanted to know what had happened and why. And he managed to convince his church and it’s parishioners to be interested too. They created an investigative board, distinct from the Town Council (or whatever) who basically didn’t buy Snow’s argument. Neither did Whitehead at first. But he was a scientist at heart. He collected all the different theories for how cholera spread and, one by one, tried to show why they were wrong. Key word. He did not try to prove an explanation, but to disprove every explanation.

And he did. The board came up with all kinds of explanation, and Whitehead waded through the death records and locations of cases and showed why they all couldn’t be true. Except for Snow’s explanation. He couldn’t find good evidence to contradict that one. And then he went out and found the index case, and showed that the house where the index case lived had a cesspool that drained into the well. Voila! Quod eratdemonstrandum.

So it was Snow’s theory, but a key component of the proof was disproving the other theories and realizing that in doing so, only Snow’s fit. And that was Whitehead’s contribution.

The book is well written, and has lots of good info about London of the time, cholera, the people involved, etc. I’m enjoying it. One downside: it’s actually about a 50 page story but has been dragged out to over 200. So things are over-elaborated.

None-the-less, it’s a good read. It’s inspired me to find Snow’s original papers (here), and I plan to read through some key ones sometime soon.

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