WINSTON-SALEM, N.C. – Jan. 31, 2013 – Some people with the flu emit more of the air-borne virus than others, suggesting that the current recommendations for infection control among health care providers may not be adequate, according to a new study from researchers at Wake Forest Baptist Medical Center.
The study is published in the Jan. 31 online edition of The Journal of Infectious Disease.
"Our study provides new evidence that infectiousness may vary between influenza patients and questions the current medical understanding of how influenza spreads," said Werner Bischoff, M.D., Ph.D., assistant professor of infectious diseases at Wake Forest Baptist and lead author of the study. "Based on our findings, doctors and nurses may need to wear a fitted respirator even for routine care of flu patients as opposed to just the non-fitted, surgical facemask currently recommended."
In the study, 94 patients at Wake Forest Baptist were screened for flu-like symptoms during the 2010-2011 flu season. Nasal swabs were collected from each patient, and air samples were obtained from within 1 foot, 3 feet and 6 feet of patients during routine care.
Of the 94 patients, 61 tested positive for the flu virus and 26 released influenza into the air. Five of the patients emitted up to 32 times more virus than the others.
"One out of five influenza-emitting individuals released elevated amounts of virus into the environment, pointing to a highly infectious subgroup," Bischoff said. "Additionally, the patients who emitted more virus also reported greater severity of illness."
Medical wisdom is that the flu virus spreads primarily by large particles traveling only 3 to 6 feet from an infected person. Current infection-control recommendations for health care providers have focused on preventing transmission by large particles and have required fitted respirators only during aerosol-generating procedures, such as bronchoscopy, intubation and cardiopulmonary resuscitation.
The Wake Forest Baptist researchers discovered that the majority of influenza virus in the air samples tested was found in small particles during routine care up to 6 feet from the patient's head. These small particles can float in the air for hours and travel relatively long distances, Bischoff said. In addition, the smaller virus particles more readily penetrate the non-fitted protective masks.
Further studies are needed to establish person-to-person transmission of influenza and to determine if "super emitters" actually spread the flu to more people, Bischoff said.
Co-authors of the study are Katrina Swett, M.S., Iris Leng, M.D., Ph.D., and Timothy Peters, M.D., of Wake Forest Baptist.
Support for the study was provided by the Centers for Disease Control and Prevention contract 200-2010-35705.
The Journal of Infectious Diseases