COLORADO SPRINGS, Colo. -- Researchers at the U.S. Air Force Academy have determined that the H1N1 virus may stick around in the nasal passages of infected people longer than anticipated.

The researchers were able to study 134 cadets with confirmed cases of H1N1 and 33 cadets with suspected cases during a major outbreak of the disease last July.

"We collected (nasal) specimens from the cadets about every other day," said Lt. Col. Catherine Takacs Witkop, one of the doctors who conducted the study.

Those specimens showed that one fourth of the patients were still shedding the virus seven days after the onset of their symptoms, and that 19 percent of them were shedding the virus after being symptom-free for 24 hours.

"What this means is that some people could be going back to work or back to school and still have the virus present in their nasal passages. Whether they’re transmitting the virus is not exactly clear," Witkop said.

Witkop said it's possible that people could still transmit the virus after being symptom-free for 24 hours.

She said as mild as the outbreak has been, the recommendation from the Centers for Disease Control and Prevention about staying away from people until you've been symptom free for 24 hours is valid for the general population, but she said people who work with at-risk populations are different.

"Those organizations may want to consider the findings of our study and perhaps extend the isolation periods of those who are diagnosed with H1N1 because of the possibility that those individuals may be transmitting the virus more than 24 hours after they've been symptom-free," she said.

Witkop said H1N1 outbreak at the Air Force Academy began shortly after a fireworks display on July 4.

She said the affected cadets were isolated into a wing of one of the dorms and that health care professionals were able to prevent further spread of the disease.

Witkop said Air Force Academy researchers hope their study will help other doctors as more outbreaks occur across the country.

"Hopefully, more studies can be done that can better determine the characteristics of this virus," she said.

The findings of the Academy study have been published in the American Journal of Preventive Medicine.