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Meanwhile, top virologists in the U.S., Canada, Hong Kong, Germany and several other nations have linked up to create a sort of virtual research lab. Their goal: to understand the virus itself. They identified the SARS virus several weeks ago, and now they are trying to come up with diagnostic tests. That's crucial. Early SARS cases present the same fevers, muscle aches and diarrhea as flu victims, and without a way to distinguish between them, the public-health system could be quickly overwhelmed.
The virtual lab and independent biotech companies have already come up with several tests, but they are not yet reliable enough to be widely deployed. Canadian microbiologists reported last week that as many as 40% of their SARS patients did not test positive for coronavirus. That might be because their tests are not sufficiently sensitive or, even more worrisome, because the coronavirus has mutated enough to elude detection.
Yet another open question is precisely how the disease spreads. Doctors first concluded that the agent responsible for SARS is transmitted by droplets expelled by coughs or sneezes. After the burst of cases in Hong Kong's Amoy Gardens complex and the particularly aggressive spread of SARS in Toronto among health-care workers, however, scientists now speculate that there may be other mechanisms as well. In Amoy Gardens, for example, transmission may have occurred via contaminated fecal matter leaking from a broken sewage pipe. That would explain the lack of direct contact, as well as the fact that all these cases, unlike those in mainland China and Toronto, are characterized by severe diarrhea.
--RAPID MUTATION
It may also be that the microbe has mutated into several subtly different strains producing different symptoms. This might explain some of the perplexing transmission patterns seen on planes: people sitting next to SARS victims did not always get infected, while those across the aisle sometimes did. Perhaps the latter had used a lavatory immediately after an affected passenger.
Multiple strains would not be surprising. This bug's genetic code is based on RNA, a single-stranded molecule very similar to DNA. Unlike DNA, however, RNA has no built-in proofreading mechanism to fix mistakes in the replication process. Most of these don't amount to anything, but every once in a while an error may make the microbe more infectious. Beyond that, says Dr. Robert Webster, chief of virology at St. Jude Children's Research Hospital in Memphis, Tenn., "when a virus comes across to a new host, what does a virus do? It varies like crazy."
In Toronto health-care officials are especially alarmed by the high number of SARS cases among health-care workers who had taken all the recommended precautions, including wearing gloves, masks and gowns and vigorously washing their hands. The problem there may have been fatigue and complacency in the changing room. CDC scientists reported last week that the virus can survive as long as 24 hours outside the body: doctors and nurses who touch their protective gear while changing into regular clothing may be unwittingly exposing themselves and others to the coronavirus.