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Breathing can transmit flu, study finds

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January 20, 2018

Patients with confirmed influenza can contaminate the air around them without coughing or sneezing, meaning the virus may spread easier than previously thought, according to researchers.

“People with flu generate infectious aerosols even when they are not coughing, and especially during the first days of illness,” Donald K. Milton, MD, MPH, professor of environmental health at the University of Maryland School of Public Health, said in a press release. “So when someone is coming down with influenza, they should go home and not remain in the workplace and infect others.”

Milton and colleagues analyzed 218 exhaled breath samples from 142 patients with confirmed influenza. The samples were obtained over the first 3 days after symptom onset during 30-minute sessions of natural breathing, talking, spontaneous coughing and sneezing. The participants also provided 218 nasopharyngeal (NP) swabs.

Infectious viral particles were recovered from 39% of breath samples and 89% of NP swabs. Detectable influenza RNA was identified in 11 (48%) fine aerosol samples that were collected during sessions when no coughs were observed. Of these, eight contained infectious viral particles. According to the researchers, sneezing was rare and did not appear to significantly contribute to viral shedding in aerosols.

“The study findings suggest that keeping surfaces clean, washing our hands all the time, and avoiding people who are coughing does not provide complete protection from getting the flu," study author Sheryl Ehrman, PhD, Don Beall Dean of the Charles W. Davidson College of Engineering at San José State University, said in the release. "Staying home and out of public spaces could make a difference in the spread of the influenza virus."

The researchers also found that self-reported influenza vaccination during the current and previous season was associated with a greater amount of viral shedding in aerosols. Participants vaccinated during both seasons had 6.3 (95% CI, 1.9-21.5) times more viral shedding than unvaccinated participants. The association was statistically significant only for influenza A viruses (P = .03).

“The association of current and prior year vaccination with increased shedding of influenza A might lead one to speculate that certain types of prior immunity promote lung inflammation, airway closure and aerosol generation,” the researchers wrote. “This first observation of the phenomenon needs confirmation. If confirmed, this observation, together with recent literature suggesting reduced protection with annual vaccination, would have implications for influenza vaccination recommendations and policies.” – by Stephanie Viguers

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Disclosures: The authors report no relevant financial disclosures.

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