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Can SARS infect without symptoms?

Researchers in Vietnam are studying more than 300 people who remained healthy despite being in close contact with those infected with SARS.
/ Source: The Associated Press

Vietnam may have contained SARS, but its health experts haven’t exactly been twiddling their thumbs. They’re studying more than 300 people who remained healthy despite being in close contact with those infected with SARS during the outbreak in Hanoi that killed five of the 63 infected.

Since the World Health Organization announced April 28 that Vietnam had an upper hand on SARS, or severe acute respiratory syndrome, researchers have been scurrying to interview and take samples from people who appeared to avoid the illness, despite close contact with infected patients.

WHO team coordinator Aileen Plant said she’s betting some of that group actually caught the disease without exhibiting any symptoms, as is the case with many other viruses. If that’s true, she said it will be good news because more people worldwide will likely have developed immunities to the virus through their exposure, instead of just those who displayed symptoms.

All of Vietnam’s cases have been linked to direct contacts.

“My gut feeling is that eventually we will be able to say that some people got infected with SARS and we didn’t know they were a public health risk,” Plant said. “We don’t think they were able to transmit the disease.”

Testing for SARS antibodies
The team’s studies come at a time when WHO experts in other countries, such as neighboring China, are still too busy trying to contain the disease to even think about tracking down those who may have been asymptomatic.

“We think that we’ll find it,” said Sharon Bloom, an epidemiologist from the U.S. Centers for Disease Control and Prevention. “Several other countries are still in the midst of controlling the outbreak, but we’re in a position now to show in Vietnam if they had (asymptomatic infections).”

The samples were sent for analysis to labs in Vietnam, Japan, Britain and the United States. The last specimens were sent the first week in June and it will likely take several weeks before the results determine whether those tested have SARS antibodies, signaling they were also infected even though they did not fall ill.

'A really big puzzle'
For instance, Plant said when the outbreak occurred at the Hanoi French Hospital in late February, only seven of the 107 patients became infected.

However, dozens of hospital workers came down with the disease that spread quickly from an American businessman who came to Hanoi from Hong Kong. He was later dubbed the communist country’s “index case” because all other infections have been linked back to him.

In contrast, no health care workers at Bach Mai Hospital showed symptoms despite also treating numerous SARS patients.

“I think that (the studies) are important,” said Pascale Brudon, the WHO representative for Vietnam, who added the organization is also interested in studying relapse rates. “In Vietnam, we’ve got a good database of all 63 (SARS) patients, so we hope that we can get something out of it.”

The researchers are hopeful the lab results will once again allow Vietnam — the first to identify the disease — to contribute to a larger understanding of the virus which, worldwide, has claimed more than 770 lives and counting.

“It’s like a really big puzzle,” Plant said. “And we’ve only got a few pieces.”