Report: SARS Can Spread Through Air
Virus-Laden Plume Spread SARS in 2003 Hong Kong Outbreak
Detective Work Pays Off continued...
Ignatius T.S. Yu, MD, PhD, of the Chinese University of Hong Kong, and colleagues thought otherwise. They obtained detailed floor plans, site plans, and weather reports for Amoy Gardens on the dates in question.
Using sophisticated airflow-dynamics studies, Yu's team showed that a SARS-laden air plume rose up from the drainage pipes through floor drains with faulty seals. The air plume was carried outside by exhaust fans and blown by prevailing wind patterns into some apartments but not others.
Yu and colleagues describe the spread of the killer air plume in chillingly scientific language. Here's an excerpt from their report in the April 22 issue of The New England Journal of Medicine:
"Virus laden aerosols generated in the [drainage pipes] of unit 7 in building E returned to the bathroom through the dried-up seals of the floor-drain traps and then entered the air shaft, probably by means of suction created by an exhaust fan. The aerosols moved upward owing to the buoyancy of the warm, humid air within the airshaft and could enter apartment units that bordered the airshaft on the upper floors because of the negative pressure created by the exhaust fans or the action of wind flows around the building. The horizontal spread of infection to other units in building E was by movement of the air between apartment units. After the plume reached the top of the air shaft in building E, the virus was spread to some units at certain heights in buildings B, C, and D by the action of a predominant northeasterly wind."
Over the next few days, 187 people from the apartment complex came down with SARS.
Airborne SARS -- and Flu?
This scenario does not mean that SARS necessarily spread though the air in explosive outbreaks, note Chad J. Roy, PhD, MSPH, and Donald K. Milton, MD, DrPH, in an editorial accompanying the Yu report. Roy is with the U.S. Army Medical Research Institute of Infectious Diseases; Milton is with the Harvard School of Public Health.
Indeed, they say, less infectious patients likely spread the virus through droplets as has commonly been thought.