One of the great tales of public health, imbibed with all students on their Masters of Public Health course, is that of John Snow and the Broad Street pump. Sidney Chave’s tabulation of the daily cases illustrates how the epidemic had already peaked on 1 September, whereas Snow removed the handle off the pump on 8 September. The secret to success in public health, the cynic has argued, is to ride the downward wave of epidemics.

Meanwhile in 1854, 200 miles up the road in Liverpool, England’s first Medical Officer of Health, William Henry Duncan was tackling another outbreak attributed to direct contagion in the grossly overcrowded slums. That outbreak peaked around 22 September. Was it affected by Duncan’s measures, based on environmental hygiene?

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