HONG KONG, the gateway to the world for the SARS virus, was this week removed from the World Health Organization鈥檚 list of affected countries, after 20 days without any new cases. But worrying evidence has emerged in Canada that the SARS virus might infect people without causing any recognisable symptoms, meaning the virus could lurk undetected even after obvious cases stop appearing.
At a global meeting on SARS in Kuala Lumpur last week, the outgoing head of the WHO, Gro Harlem Brundtland, declared that strenuous efforts to isolate cases and quarantine their contacts had stopped SARS 鈥渄ead in its tracks鈥�. Only Toronto and Taiwan remain on the WHO鈥檚 list of areas where there is still local transmission.
But at the same meeting, Nigel Gay of the UK Health Protection Agency warned that these methods are not enough to eradicate the SARS virus if it can infect and be passed on by people who do not develop any symptoms 鈥� and are therefore not quarantined. So health officials are worried by the discovery of SARS virus in 120 people in Canada who were not diagnosed with the disease.
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Frank Plummer, scientific director of Canada鈥檚 National Microbiological Laboratory in Winnipeg, announced last week that DNA tests had revealed evidence of the SARS virus in the blood of 120 people who, in March, either had suspicious symptoms, or contact with a case. None of these people was ever diagnosed with SARS.
The crucial question is whether people with this kind of mild infection can pass on the virus to others. 鈥淭here is good evidence that they did not spread the disease,鈥� said James Young, Ontario鈥檚 commissioner of public safety, at a press conference last week.
But one of the criteria for diagnosing SARS is whether a patient has been in contact with a known case, so someone who caught it from a person who has an unrecognised infection might also be missed, especially if they too failed to develop obvious symptoms. Plummer鈥檚 team is now trying to track down the 120 people to see if they have antibodies to SARS, which would confirm that they had a real infection. It is also tracing contacts of these people to see if any of them show signs of SARS infection.