Airborne influenza transmission possible through exhalation

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Influenza infections are independently compartmentalized in the upper and lower airways.
Influenza infections are independently compartmentalized in the upper and lower airways.

Airborne influenza infections may be transferred by breathing, without the need for sneezing and coughing, according to a study published in the PNAS.

Jin Yan, PhD, from the Maryland Institute for Applied Environmental Health of the School of Public Health at the University of Maryland and associates, conducted a series of tests to determine if virulent influenza could be transmitted through normal or forced exhalation, such as normal breathing, speaking, coughing, and sneezing.

The investigators tested 355 volunteers (ages 19 to 21) with acute respiratory illness for influenza. Of the volunteers, 142 tested positive for influenza; 89 patients had influenza A, 50 patients had influenza B, and 3 patients had influenza A and B.

These eligible patients gave both nasopharyngeal and 30-minute breath samples (218 total samples). Viral RNA extracted from breath samples was defined as coarse aerosol (>5 µm) and fine aerosol (≤5 µm) segments. Viral RNA was detected in fine-aerosol (76%), coarse-aerosol (40%), and nasopharyngeal (97%) samples.

The quantity of influenza virus RNA was not associated with cough frequency (number of coughs in 30 minutes) in nasopharyngeal samples and weakly associated with coarse-aerosol samples. Fine-aerosol samples had some association with 48% of samples containing viral RNA.

A significantly higher coughing rate was noted in female candidates, while their male counterparts had a 3-fold greater rate of viral RNA in their fine-aerosol coughs.

The researchers reported that 89% of nasopharyngeal samples and 39% of fine-aerosol extractions contained virulent samples, indicating that patients with influenza can release infectious viruses that can remain airborne for lengths of time.

“Surprisingly, no symptoms, including lower respiratory and systemic systems, were strongly associated with shedding into aerosols, in this population with relatively mild lower respiratory symptoms,” the authors noted. “Thus, we can conclude that the head airways made a negligible contribution to viral aerosol generation and that viral aerosols represent infection in the lung. Moreover, upper and lower airway infection appear to behave as though infection is compartmentalized and independent.”

Reference

  1. Yan J, Grantham M, Pantelic J, et al. Infectious virus in exhaled breath of symptomatic seasonal influenza cases from a college community. PNAS. 2018 Jan 18. doi:10.1073/pnas.1716561115 
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