More than 100 new cadets at the U.S. Air Force Academy got infected with swine flu at a July 4th barbecue and fireworks display but quick isolation measures got it under control within two weeks, researchers reported on Tuesday.

The outbreak provided a unique opportunity to study the virus closely and Dr. Catherine Takacs Witkop and colleagues say they discovered some surprising things. Among them:

* Nearly a quarter, or 24 percent, of patients still had virus in their noses seven days after getting sick, including 19 percent who had been well for at least 24 hours

* Tamiflu, the drug used to treat influenza, did not help any of the previously healthy young men and women get better any quicker.

* Most cadets were sick for five days or longer.

* Eleven percent of the cadets became infected.

In June, soon after the new H1N1 virus was declared a pandemic, 1,376 new cadets arrived for their first training at the academy, near Colorado Springs, Colorado.

“A total of 134 confirmed and 33 suspected cases of new H1N1 infection were identified with onset date June 25-July 24, 2009,” Witkop’s team wrote in the American Journal of Preventive Medicine.

The cadets, unusually young and healthy, all did well and none became seriously ill or died. Most cases were traced to a July 4 party for the cadets, Witkop said.

“It was about 48 to 72 hours later that we saw the increase in the cadets presenting with the symptoms,” Witkop said in a telephone interview.

Witkop said the academy doctors quickly designated one dormitory for the sick cadets and kept them away from the others.

They tested them daily for the virus, painting a picture of the course of the disease far more detailed than has been possible before.

IN THE NOSE

Eleven, or 19 percent of nose washes taken from 58 patients who had been free of symptoms for a full 24 hours still contained virus, although it is not clear if the patients were still contagious.

“If a cadet is no longer coughing or sneezing, how likely this virus is to be transmitted is still a question,” Witkop said.

The U.S. Centers for Disease Control and Prevention advises that H1N1 patients can return to work and school 24 hours after their symptoms such as fever go away.

Many of the cadets were treated with oseltamivir, the pills sold by Roche AG under the Tamiflu brand name, but they did not get better any more quickly than untreated cadets.

“We did use it in the hope that we would stem the tide of the outbreak but I don’t think the Tamiflu was the key player in the outbreak resolution,” Witkop said.

“I think it was ... the isolation protocol,” she added. Cadets stayed in the sick dorm until they were free of symptoms for 24 hours, or for seven days after first getting sick, whichever was longer.

The CDC recommends saving Tamiflu for people most at risk of getting severely ill from flu, such as pregnant women, people with diabetes or asthma or disabled children.

The academy also quickly educated the cadets about washing hands and not spreading germs by covering their coughs, and Witkop said they used a great deal of hand sanitizer, which may have helped control the outbreak within 10 to 14 days.

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By Maggie Fox, Health and Science Editor

WASHINGTON (Reuters)