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Infectious flu particles reach as far as 6 feet
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Patients in the hospital with influenza could potentially spread influenza virus particles as far as 6 feet by air, researchers from Wake Forest University have found, potentially exposing health care workers to small infectious particles.
“The CDC [and others] have expressed lack of knowledge and the urgent need for research in influenza virus transmission routes,” the researchers wrote in the Journal of Infectious Diseases. “CDC and WHO state that influenza virus transmission primarily occurs by large-particle respiratory droplets traveling within a short distance of the source and that such particles are blocked during encounters between patients and health care professionals.”
The researchers evaluated 94 patients with influenza-like illness who were admitted to the ED or inpatient care. The patients provided nasopharyngeal swab specimens, and the researchers evaluated air samples at distances of 1 foot, 3 feet and 6 feet from the patient’s head.
Sixty-one patients tested positive for influenza, and 26 of these patients released influenza virus into the room air. At all sample locations, the airborne 50% human infectious dose of influenza virus was surpassed. Health care workers were mainly exposed to small influenza virus particles, and the concentrations decreased as they went farther from the patient.
The release of influenza virus into the air was associated with higher nasopharyngeal viral load. Among patients with a higher viral load, coughing and sneezing were associated with increased influenza virus release. Five of the virus emitters released 32 times more influenza virus into the air, and these patients had more severe illness.
“We found that patients produced mostly small influenza virus-carrying particles during routine, non-aerosol-generating care activities,” the researchers wrote. “Health care professionals could be exposed to infectious doses of influenza virus at a distance of 6 feet from patients, with small particles potentially exceeding the suggested exposure zones. This raises concerns regarding the adequacy of protection afforded to health care professionals by the current recommendations during routine care.”
In an accompanying editorial, Caroline Breese Hall, MD, of the University of Rochester School of Medicine and Dentistry in New York, wrote that it is important to better understand influenza transmission, especially because global travel presents the risk for a worldwide influenza outbreak.
“A tenable conclusion from these findings is that infection control procedures should be commensurate with the concern generated by the clinical observations of the intensity and severity of the community outbreak,” she wrote.
Disclosure: The researchers report no relevant financial disclosures. Breese Hall has consulted for GlaxoSmithKline and MedImmune.
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