Biologists seek to head off future sources of infection

and Alison Abbott, Munich A 33-floor apartment block in the bustling Kowloon district of Hong Kong could provide clues to the true risk posed by severe acute respiratory syndrome (SARS), epidemiologists say. Scientists around the world are racing to gather data that will allow epidemiologists to predict whether SARS is likely to become a full-blown pandemic. Their search has led them to investigate exactly what happened when the disease surged through the Hong Kong residential complex in March. The study, which is being led by Wilina Lim, head of virology at the Hong Kong Department of Health, is the world’s only large-scale investigation of the extent to which people without symptoms are carrying SARS — a critical question for those seeking to predict the epidemic’s likely reach. “The key issue is whether symptomless carriers can infect others, and for how long they can do so,” says Albert Osterhaus, head of the Netherlands National Influenza Centre in Rotterdam. “If carriers are symptomless for extended periods, a pandemic is quite possible. If not, the epidemic is likely to be controlled.” As of 28 April, 131 cases of SARS had been confirmed among residents of Block E of the heavily hit Amoy Gardens apartment complex in Kowloon. And 241 symptomless residents were quarantined on 1 April for 10 days following the local outbreak. Just over 100 of the quarantined residents are taking part in Lim’s study, the results of which, she says, should be known by midMay. The researchers are trying to take throat samples from the participants every other news