Originally published in MedPage Today
by Michael Smith, MedPage Today North American Correspondent
The finding comes from an analysis of an outbreak in a Pennsylvania elementary school in May and June, according to Achuyt Bhattarai, MD, of the CDC.
Analysis of a series of specimens from affected children and their household contacts also showed that younger children tended to shed the virus longer than older kids, Bhattarai told attendees at the annual meeting of the Infectious Diseases Society of America.
Earlier this year, researchers reported that adults infected with the H1N1 pandemic flu strain continue to shed virus after the point where current recommendations say they can go back to work or school.
But those researchers said — and Bhattarai concurred here — that it would be a leap to assume that shedding virus means a person remains contagious. Among other things, modern tests are so sensitive they can detect virus in amounts so small that contagion is all but impossible, the experts said.
The CDC currently recommends that people with flu-like symptoms stay home until at least 24 hours after they are free of fever without using fever-reducing medicines.
Bhattarai and his colleagues used two methods to detect virus in 26 people — including four adults — affected by the Pennsylvania outbreak. They used real-time reverse transcriptase polymerase chain reaction (rRT-PCR) to detect viral particles and culture methods to find viable virus.
Overall, he said, the median time from onset of fever to the end of shedding was six days using RT-PCR. Viable virus was detected using culture for a median of five days after the start of fever, he said.
But for children younger than 5, the median was eight days by PCR and five by culture, compared with six days for both methods for kids ages 5 through 9 and five for both methods in kids ages 10 through 18.
The four adults in the analysis stopped shedding a median of four days after the start of fever on both PCR and culture, Bhattarai said.
The findings start to tease out the factors that will help health officials decide when children should go back to school, according to Andrew Pavia, MD, of the University of Utah. Pavia was not part of the study, but moderated a news conference at which it discussed.
He noted that the pandemic flu appears to attack differently than the seasonal flu in that young people tend to get sicker than older adults, which is the opposite of what happens with seasonal flu.
One way to avoid the issue is to vaccinate children against the pandemic flu, according to Bruce Gellin, MD, director of the National Vaccine Program Office of the Department of Health and Human Services.
“This is clearly a novel virus, but it’s not a new vaccine,” he told reporters. “The swine flu vaccine is made exactly the same way as the seasonal flu vaccine,” and there are no differences in terms of safety.