More SARS or Just a False Alarm?

Share

More SARS or Just a False Alarm?

Twelve patients in nursing homes in Canada have tested positive for the virus that causes SARS. Yet health officials say all 12 of the tests are wrong.

The outbreak began in July at a nursing home in Surrey, a town near Vancouver. Cold-like symptoms spread among 143 residents and staff, and 10 elderly residents developed pneumonia. Six of them died, which is not atypical in a nursing home.

Genetic samples of the patients were sent out as a precaution to scientists at the National Microbiology Laboratory in Winnipeg. They found the virus that causes SARS in patient samples.

Later, two other labs, the Genome Sciences Centre and the British Columbia Centre for Disease Control, both in Vancouver, said they did not find evidence of SARS in samples from the nursing home patients, leading health officials to declare a false alarm.

The WHO issued a press release Monday saying, "This outbreak has no international public health implications."

But researchers said the initial tests wouldn't have come up with an exact SARS match if the disease were not there, and that Canadian officials are practicing damage control to avoid further economic harm to a country that suffered major business losses earlier this year during the SARS epidemic.

"Fraser Health has been spinning this story very hard, and Promed and the World Health Organization are going along," said Harvard professor Henry Niman, who has followed SARS closely. "Anyone not paying close attention is falling victim to the spin." Fraser Health oversees the affected nursing homes.

Niman has studied the data and believes there's no question that SARS is present in the samples. Either the patients had SARS, he said, or the lab equipment was contaminated with it.

"One screamingly obvious trivial explanation (is) that the sequence reported was amplified from laboratory contaminants that carry the SARS CoV nucleic acid sequence," said John Ashkenas, a SARS researcher at Mt. Sinai Hospital in Toronto. "Anyone who's worked with PCR (a technology that amplifies genetic material so it can be measured) can tell you how easy it is to contaminate the lab."

Such contaminants pose no health risk – they are harmless bits of DNA. But they can cause a PCR test to turn up positive results repeatedly.

That explanation is looking less likely, Niman said, because the samples show exact matches to two different strains of SARS. It's very unlikely that the Winnepeg lab was contaminated with two separate strains of the virus, he said.

Blood tests of two other patients from the nursing homes also tested positive for SARS antibodies, which arise in those infected with SARS in order to fight off the virus. However, no one else has been able to duplicate those tests, leading researchers to question their veracity and further adding to the debate over whether SARS has re-emerged.

David Patrick of the British Columbia Center for Disease Control gave yet another possible explanation for the outbreak. He told National Public Radio Tuesday that researchers may be mistaking SARS for a similar virus called OC43, which sometimes causes the common cold.

But Niman said the SARS coronavirus must have been present in the samples, whether by contamination or from the patients, because the gene sequences are an exact match.

The Winnipeg lab has reported questionable results in the past. In March, researchers there stated that human metapneumovirus caused SARS. It turned out to be a coronavirus, in the same family as the common cold.

"I suspect (the Winnipeg lab) also was wrong in April-June when they found (greater than) 100 asymptomatic people were testing 'positive' for SARS," said Barry Armstrong, a general surgeon in Dryden, Ontario, who has followed the SARS epidemic closely. "What was the cause, what breach of their laboratory technique? I do not know."

If this outbreak does not turn out to be SARS, that doesn't mean health officials can breathe easy. Armstrong cautioned that a return of SARS remains a worrisome possibility. He also said to expect more incidents like this most recent potentially false outbreak in Canada.

"To be certain that SARS will be spotted, we must accept a few false alarms," Armstrong said. "The Surrey outbreak was such a false alarm."