Is a miasma to blame?
No. Shitty water.
John Snow (no, not that guy) died 160 years ago today. He is most famous for tracing the source of the 1854 cholera epidemic in Soho to a water pump where the mother of an afflicted infant rinsed the soiled diapers. (How did the poor kid get cholera to begin with? The waterworks company was pumping in water from polluted parts of the Thames.) Remove pump handle and bam, no more epidemic. So fuck you, miasma theory. John Snow thinks you’re shit.