There was a famous case of a 50 storey residential building where people in different stages infected each other - apparently by aerosols dispersed through sewage vents. That happened a decade ago - the SARS virus that caused 342 confirmed cases and 42 deaths in the complex. The virus was transported by air droplets escaping from dry U bends (siphons) and negative pressure in the bathrooms caused by extractor ventilators. See the interactive graph above. The interconnectedness of the sewage system not only in the same building but between nearby complexes (such as hospitals) facilitates the dispersion of pathogens. Recently the Lancet recommended (1) investigate the sources of sewage odors, (2) maintain the U bends full all the time opening the tap twice a day for 5 minutes.
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