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High Humidity Reduces Flu Virus Infectiousness

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MONDAY, March 4 (HealthDay News) -- The influenza virus becomes less infectious at high relative humidity, according to a study published Feb. 27 in PLOS ONE.

John D. Noti, from the U.S. Centers for Disease Control and Prevention in Morgantown, W.Va., and colleagues used Bioaerosol samplers to collect size-fractionated aerosols of nebulized influenza coughed into an examination room (<1 µM, 14 µM, and >4 µM aerodynamic diameters) adjacent to the breathing manikin's mouth and also at other locations within the room. The room was held at constant temperature, but the relative humidity was varied from 7 to 73 percent. Infectivity was assessed by a viral plaque assay.

The researchers found that total virus collected for 60 minutes retained 70.6 to 77.3 percent infectivity at relative humidity ≤23 percent but only 14.6 to 22.2 percent infectivity at relative humidity ≥43 percent. There was a similar loss in infectivity among the individual aerosol fractions. Most of the loss in infectivity within each aerosol fraction occurred 0 to 15 minutes after coughing, according to time interval analysis. Continued losses in infectivity occurred up to five hours after coughing; however, the rate of decline at 45 percent relative humidity was not statistically different than that at 20 percent regardless of the aerosol fraction analyzed.

"At low relative humidity, influenza retains maximal infectivity and inactivation of the virus at higher relative humidity occurs rapidly after coughing," the authors write.

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