Cholera, Spatial Thinking and John Snow: Soho 1854

A particularly bad outbreak of cholera in Soho in 1854 led one man to identify contaminated water as the mode of transmission and apply one of the most famous instances of spatial thinking.

At a time when the fledgling Canterbury colony was getting itself sorted out, the London of 1854 was a stinking, festering hell-hole.  Growing from the tiny Roman town of Londinium, through the medieval ages and then in to a city of over two million souls, the place was overrun by filth.  Sewage flowed freely in the street and abattoirs operated down mews and alleyways, blood and gore washed away with each rain.  The Thames, a source of drinking water for many, was little more than an open sewer.

To deal with human waste, buildings and homes tended to have cesspits in their basements (which I won’t show you any pictures of), which were periodically emptied by the lower echelons of society, and conveniently disposed of in the Thames.

At the time, London’s sewer system was limited and water for drinking and washing was piped to public water pumps on street corners, often straight from the river.  Not alone amongst European cities, cholera was an ongoing problem, having already suffered through recent outbreaks where well over 10,000 people were killed.

There’s nothing pleasant about cholera – it’s a horrible way to die.  Symptoms include severe diarrhea and vomiting leading to irreversible dehydration.  Once contracted, a person can die within painfully slow hours to days.

At that time, no one had a clear understanding of how the disease was transmitted.  The predominant idea was that it was air-bourne, a miasma that seeped up from underground.  After all, as the city grew beyond its Roman city walls, it expanded over cemeteries and offal pits, many of which contained bodies of those killed by the Black Death.  Most efforts at controlling cholera focused on air quality.  But some were skeptical of that notion, and one John Snow in particular.

A physician and anaesthetist (to the Queen, no less), he had already tied Thames water to outbreaks, but not many paid attention.  He was actively investigating water as a mode of transmission when a particularly bad outbreak occurred in Soho, west London.  Over the course of three days, over 500 people died, and he wanted to know why.

So he talked to people in Soho and looked in detail at the records of deaths.  This record contained basic information about each person; name, age, and address, amongst other things (an analog spreadsheet of sorts).  As part of his investigations, he did something which these days we might think obvious – he translated the deaths in the record book on to a map and looked for any patterns.  Here’s a copy of that map:

On this map, he plotted the number of deaths occurring at an address as a sort of stack of small rectangles: the more deaths, the longer the stack. Our human wetware can look at this and fairly easily pick up a sort of pattern, a clustering of deaths around a point.  Here’s a bit of detail from the map:

And roughly at the centre of this cluster sat a public water well.  Armed with these insights, Snow was able to convince the town officials to remove the handle of the pump to prevent its use, and the new cases of cholera dropped off almost immediately.

Later investigations showed that the pipe feeding the water pump had become damaged and the contents of a cesspit from an adjacent house had been leaking directly into the water line –  a baby had recently died from cholera at that house.  People were essentially drinking cholera contaminated raw sewage.

An interesting thing to note – there were relatively few deaths at the large workhouse just to the north of the water pump, even though everyone living and working there got their water from the same source.  Why so few?  It was a brewery.  The brewing process effectively killed off the cholera bacteria and is a great way to purify contaminated water (as our FESD dean will no doubt agree) practised over centuries.

Several important things follow from this event.  First, the connection between contaminated water and cholera was established, setting the scene for not just London, but many other cities around the world, to undertake huge public works projects to build reticulated water and sewer systems and transforming the sanitary conditions for city dwellers – some would argue that this was the beginning of modern cites as we know them.  Secondly, the fledgling science of modern epidemiology got its start from Snow and his investigations.  Thirdly (and most pertinently here), this is a great example of spatial thinking.  Any GIS course that doesn’t mention Snow is likely doing a disservice to its students (IMHO).  Geographers from around the world will still make a pilgrimage to the water pump monument on the corner of what is now Broadwick and Poland Streets to pay tribute to this event (your humble author included).

Incidentally, the original water pump was on the corner of Broad and Lexington Streets, where the John Snow pub now stands.

(If you make it there yourself, be sure to call in to Flat White, just around the corner in Berwick Street for a proper cup of coffee, New Zealand style.) 

This is a great example of how incorporating location into your investigations (spatial thinking) can provide you with additional insights.  Spatial thinking is another arrow in your quiver of methods to understand phenomena.  Not all problems will have a spatial component but for those that do, spatial thinking (and GIS) are a great tool at your disposal.

This is also a great example of using a map to communicate information, to tell your story.  For many, Snow’s map was a compelling factor in convincing them of the connection between the water and the outbreak.  The simple act of mapping the deaths led to an easier to grasp pattern than what could be gleaned from the spreadsheet of deaths.  In another post we’ll look at how we can work with Snow’s spatial data to meaningfully display them in different ways.

Sadly, cholera remains a significant problem today, being especially a risk in areas of poor sanitation and often the number one concern after a natural disaster in populated areas.  Spatial thinking has helped to understand it but not necessarily to prevent it.

I can heartily recommend a book from our library that gives you much more detail on this event: The Ghost Map by Steven Johnson.  Well worth a read.

C