title: High humidity leads to loss of infectious influenza virus from simulated coughs.
abstract: BACKGROUND
  The role of relative humidity in the aerosol transmission of influenza was examined in a simulated examination room containing coughing and breathing manikins.
  
  
  METHODS
  Nebulized influenza was coughed into the examination room and Bioaerosol samplers collected size-fractionated aerosols (<1 µM, 1-4 µM, and >4 µM aerodynamic diameters) adjacent to the breathing manikin's mouth and also at other locations within the room. At constant temperature, the RH was varied from 7-73% and infectivity was assessed by the viral plaque assay.
  
  
  RESULTS
  Total virus collected for 60 minutes retained 70.6-77.3% infectivity at relative humidity ≤23% but only 14.6-22.2% at relative humidity ≥43%. Analysis of the individual aerosol fractions showed a similar loss in infectivity among the fractions. Time interval analysis showed that most of the loss in infectivity within each aerosol fraction occurred 0-15 minutes after coughing. Thereafter, losses in infectivity continued up to 5 hours after coughing, however, the rate of decline at 45% relative humidity was not statistically different than that at 20% regardless of the aerosol fraction analyzed.
  
  
  CONCLUSIONS
  At low relative humidity, influenza retains maximal infectivity and inactivation of the virus at higher relative humidity occurs rapidly after coughing. Although virus carried on aerosol particles <4 µM have the potential for remaining suspended in air currents longer and traveling further distances than those on larger particles, their rapid inactivation at high humidity tempers this concern. Maintaining indoor relative humidity >40% will significantly reduce the infectivity of aerosolized virus.
authors: Health Effects Laboratory Division (HELD), National Institute for Occupational Safety and Health (NIOSH), Centers for Disease Control and Prevention (CDC), Morgantown, West Virginia, United States of America. ivr2@cdc.gov
authors: John D
authors: JD
authors: Noti
authors: Francoise M
authors: FM
authors: Blachere
authors: Cynthia M
authors: CM
authors: McMillen
authors: William G
authors: WG
authors: Lindsley
authors: Michael L
authors: ML
authors: Kashon
authors: Denzil R
authors: DR
authors: Slaughter
authors: Donald H
authors: DH
authors: Beezhold
mesh_terms: D000336:Aerosols; D000818:Animals; D003371:Cough / Q000821:virology*; D006801:Humans; D006813:Humidity; D061985:Madin Darby Canine Kidney Cells; D009975:Orthomyxoviridae / Q000472:pathogenicity*; D010316:Particle Size
chemical_list: D000336:Aerosols