The current public health recommendation is that if you've been sick, you can go back to work or school 24 hours after your fever goes away, but a new study published in American Journal of Preventive Medicine says you might still be contagious.
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Last summer, 1,400 new cadets arrived at the U.S. Air Force Academy in Colorado Springs, Colo. Between June 26 and July 4, there were a few cases of flu-like illnesses, but after a party, the numbers went way up as cadets were hit hard by fever, cough, fatigue and other symptoms.
The outbreak presented Catherine Takacs Witkop and her medical colleagues at the academy with an opportunity.
"Within approximately 10 days of their arrival, we saw an increase of respiratory illnesses, and what we learned within a very short period of time was this was a novel H1N1 outbreak," Witkop says.
She and her team identified 134 cases of swine flu and 33 suspected cases — 11 percent of the cadets.
They wanted to know how soon they could send the cadets back to basic training; the Centers for Disease Control and Prevention advises that people can go back to their normal activities after 24 hours of no fever. But the Air Force Academy doctors realized no one really knew when it would be safe for people with the new H1N1 flu, so they moved fast.
The doctors asked the cadets to agree to nasal washes — a squirt of saline in their noses — and looked for any viruses that came out.
Witkop says 19 percent of cadets who had been symptom-free for more than 24 hours still had the live virus.
She says the findings suggest that people who are going to be in high-risk settings — like hospitals or day care centers or around pregnant women — should stay home longer or keep their distance.
Doing What's Practical
Dr. Anne Schuchat of the CDC says she's not surprised some of the cadets were still shedding virus.
"What's important to say is shedding doesn't mean you're spreading," she says.
And, she says, the advice remains the same.
"People should stay home for 24 hours after their fever is gone without taking anti-fever medicine," she says, "and that's really a balance of making sure that most of the transmission is prevented, and yet we're balancing how long and disruptive our interventions are."
You can't isolate people for days after they're well, says Dr. William Schaffner, head of preventive medicine at Vanderbilt University.
"It's not possible to have a plan that's completely safe," he says. "We're trying to do what's best but also do what's practical."
People are most infectious during the first couple of days of illness and a day before symptoms appear, he says. A completely safe policy would mean isolating everyone.
Schaffner says the finding is a reminder about personal hygiene — that everyone should wash their hands frequently, and when the urge to cough hits, they should do so into their elbows.
"The best way to avoid all this is to get vaccinated as quickly as possible," he adds.
Following that advice could take some time. In most states right now, the vaccine is in limited distribution, available primarily to at-risk groups such as health care workers, pregnant women, people with chronic health conditions and kids.