Tracing the Spread of SARS

By Joe Palca

Published May 16, 2003 at 12:00 AM EDT

In March, more than 300 people contracted SARS at the Amoy Gardens complex, and 35 died. The World Health Organization recently declared the complex "SARS-free."

A worker at Golden Arts Video, a shop outside the entrance to Amoy Gardens, says the fear of SARS has kept people away.

Investigators from the World Health Organization have reached a preliminary conclusion about what caused an outbreak of SARS in a large apartment complex in Hong Kong. The mere mention of Amoy Gardens causes alarm -- nearly 15 percent of all SARS cases in Hong Kong came from this one complex. NPR's Joe Palca visited Amoy, and reports that even though the buildings have been declared SARS-free, people continue to avoid the area.

Amoy Gardens consists of 19 concrete, high-rise apartment buildings. In mid March, residents of apartment block E began getting sick. Researchers at the University of Hong Kong now suggest that a single extremely ill patient caused many of the cases.

Amoy Gardens is a special case. Most people become infected with the virus when someone who is already sick coughs on them, or touch their eyes or mouth with contaminated hands. But the Amoy resident sick with SARS didn't give people the virus directly. Instead, he was excreting virus into the building sewer system. The virus then leaked into bathrooms in the apartments above and below his because of peculiarities in the drains and because venting fans were carrying the viral-laden water droplets into a common airspace.

The WHO agrees with the conclusion, but it remains preliminary.

"Of course, we cannot say that this is a complete theory nor can we say this is the only thing that explains everything, but so far it explains all the phenomena that was presented to us," says Andy Chan, part of the University of Hong Kong's investigation team.

Chan says the air plume theory explains the outbreak in apartment block E, and may explain some of the other cases in other towers. But it's also likely that many of those people became infected person to person, rather than through environmental factors.

Yguo Li, another member of the team, says the Amoy Gardens case will be studied for a long time: "It's a case with a lot of data, and it's a case where we can learn a lot things about transmission. So what we hope from the Amoy investigation is to know a bit more about transmission, and hopefully this could help develop better prevention methods in the community."