THURSDAY, Jan. 31 (HealthDay News) -- People suffering from the flu can give off small virus particles into the air at greater distances than previously thought, putting the health care workers who treat these patients at increased risk for getting the virus themselves, researchers report.

The investigators, from Wake Forest School of Medicine in North Carolina, suggest that more studies are needed on how the flu is spread. Infection-control guidelines for health care providers may also need to be updated to help these workers protect their health.

The study was published in the current edition of the Journal of Infectious Diseases.

"Our study offers new evidence of the natural emission of influenza and may provide a better understanding of how to best protect health care providers during routine care activities," the researchers, led by Dr. Werner Bischoff, wrote in the report.

For the study, Bischoff's team screened 94 patients with flu symptoms who were admitted to the emergency department or inpatient care unit of Wake Forest Baptist Medical Center during the 2010-2011 flu season. Health care providers at this hospital are required to get a flu shot, the researchers pointed out in a Wake Forest news release.

The investigators also collected air samples within one foot, three feet and six feet of the patients screened. As the air samples were taken, no aerosol-generating procedures -- such as bronchoscopy, intubation or CPR -- were performed. The researchers also recorded the number of times the patients coughed or sneezed and rated the severity of these symptoms. The patients also answered questions about their condition and how long they had been sick.

The study authors found that 65 percent of the patients tested positive for the flu. Of these people, 43 percent released particles containing the virus into the air. Those who emitted the highest levels of the flu virus into the air reported having the worst flu-like symptoms. These patients also had the highest viral loads in their collected samples.

Most of the flu virus found in the air samples was contained in small particles up to six feet away from the infected patients. Although concentrations of the virus decreased with distance, the researchers noted that at this range health care providers may still be exposed to infectious dosages of the flu.

Bischoff and colleagues also said that some patients were what they called "super emitters," and gave off up to 32 times more virus than the other patients. These people, they concluded, may be more likely to pass the flu on to others.

Dr. Caroline Breese Hall, from the University of Rochester School of Medicine and Dentistry in Rochester, N.Y., pointed out in an accompanying journal editorial that the findings "question the traditional belief that influenza is primarily spread by close contact with an infected person or by direct contact with infectious secretions."

And Dr. William Schaffner, chair of the department of preventive medicine at Vanderbilt University School of Medicine in Nashville, also commented on the study. "Influenza vaccination, although not perfect, is the best tool we have to protect health care workers -- and their patients -- from influenza illness," he said in the news release. Schaffner was not involved with the study.

More information

The U.S. Department of Health and Human Services has more about the flu.