Epidemic trees of the 3 pneumonic plague outbreaks. The vertical grey lines separate the numbered days of each outbreak. Circles and squares represent female and male cases, respectively. White and black symbols represent time of symptom onset and death, respectively. Grey symbols represent time of symptom onset for those cases that recovered. Case numbers are given above time of symptom onset symbols. Dashed connectors represent the symptomatic period and un-dashed connectors represent routes of transmission. Boxes represent different locations and dividing long-dashed lines represent different cottages. C, B, L, T and W represent Charity Farm Cottages, Brickhill Terrace Cottages, Latimer Cottages, Turkey Farm Cottages and Warren Lane Cottages, respectively.