Swine Flu Might Be Even More Contagious

Sept. 16, 2009— -- SAN FRANCISCO -- People infected with the swine flu (or H1N1 pandemic flu) strain continue to shed virus after the point where current recommendations say they can go back to work or school, two studies suggested Tuesday.

The question, experts said, is whether those people are still contagious and whether a longer stay-at-home period would prevent enough additional infections outweigh the cost.

The U.S. Centers for Disease Control currently says people should wait at least a day after their fever subsides -- usually three or four days after the onset of symptoms -- before resuming normal activities.

But patients can continue to shed virus for several days after that, according to data presented at the annual Interscience Conference on Antimicrobial Agents and Chemotherapy in San Francisco.

Even so, detection of virus doesn't necessarily mean contagion, said Dr. Gaston De Serres, of Laval University in Quebec City.

"We detected live virus," he told reporters. "We cannot say (patients are) contagious but they have the potential to be."

De Serres and colleagues studied 43 people with confirmed H1N1 pandemic flu, as well as members of their households, using polymerase chain reaction technology to detect the virus and culture methods to find live influenza.

Eight days after their symptoms started, De Serres said eight of the 43 (or 19 percent) were still shedding live virus, detected by culture methods.

Meanwhile, in a similar study, Dr. David Chien Lye, of Tan Tock Seng Hospital in Singapore reported that even after treatment with oseltamivir (Tamiflu), patients may still shed virus for several days.

Lye and colleagues studied 70 patients treated in the hospital after they showed signs of the pandemic flu. They found that 80 percent were still shedding virus after five days of illness, compared with 40 percent after seven days and 10 percent after 10 days.

The longest period during which a patient shed virus was 12 days from the start of symptoms, he said. Lye used a different method to detect the virus and wasn't able to tell whether the virus given off by the patients was a "live virus," he said. But he said a small sub-study in which both tests were used provided similar results in each instance.