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H1N1 patients may be infectious 10-plus days
By Steve Sternberg, USA TODAY
SAN FRANCISCO ? Some people who are infected with the pandemic flu appear to shed infectious virus for 10 or more days after they're infected, researchers reported Monday.
Two studies reported separately by researchers in Canada and Singapore found that roughly one in five patients continue shedding the new H1N1 virus, or swine flu, with one study suggesting that patients may still shed virus despite treatment with Tamiflu.
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The research suggests that the current prevention guidelines for "self-isolation" may not be long enough, says one investigator, Gaston De Serres of the National Institute of Public Health in Canada. Guidelines from the U.S. Centers for Disease Control and Prevention indicate that it's safe for flu patients to mingle with others 24 hours after fever abates.
With seasonal flu, people are not believed to be infectious after a week, De Serres says. The new studies indicate that some patients may still be infectious for a longer period after they fell ill with flu.
The first study, by De Serres and his team, found that eight of 43 patients, or 19%, were still shedding H1N1 virus eight days after they became ill. David Lye of Tan Tock Seng Hospital in Singapore reported that people who have been treated with Tamiflu still may shed virus for several days. In Lye's study of 70 patients, 80% of the treated patients were still shedding virus after five days of illness, 40% after seven days and 10% after 10 days. People who didn't get Tamiflu were infectious longer.
"We were a bit surprised to see patients who were still positive on Day 12," Lye told the American Society for Microbiology in San Francisco.
Neither study was rigorous enough to nail down whether people were shedding enough virus to spread infection.
"Some people will continue to shed live virus after their fever stops, we know that. The policies are intended to decrease, but not completely eliminate, infection," says Daniel Jernigan, deputy director of CDC's flu division. "If we had a virus with a very high attack rate or death rate, we might have a very different policy."
Frank Lowy, of Columbia University College of Physicians & Surgeons, says that the results should be "treated with a certain amount of caution," because the studies are small and the researchers didn't measure how much virus the patients were shedding.
Still, he says, similar results from two such far-flung sites merit further study. "It's interesting," he says. "It may help explain why the virus has spread so quickly."
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