Viable Influenza A Virus in Airborne Particles from Human Coughs

Abstract

Patients with influenza release aerosol particles containing the virus into their environment. However, the importance of airborne transmission in the spread of influenza is unclear, in part because of a lack of information about the infectivity of the airborne virus. The purpose of this study was to determine the amount of viable influenza A virus that was expelled by patients in aerosol particles while coughing. Sixty-four symptomatic adult volunteer outpatients were asked to cough 6 times into a cough aerosol collection system. Seventeen of these participants tested positive for influenza A virus by viral plaque assay (VPA) with confirmation by viral replication assay (VRA). Viable influenza A virus was detected in the cough aerosol particles from 7 of these 17 test subjects (41%). Viable influenza A virus was found in the smallest particle size fraction (0.3 μm to 8 μm), with a mean of 142 plaque-forming units (SD 215) expelled during the 6 coughs in particles of this size. These results suggest that a significant proportion of patients with influenza A release small airborne particles containing viable virus into the environment. Although the amounts of influenza A detected in cough aerosol particles during our experiments were relatively low, larger quantities could be expelled by influenza patients during a pandemic when illnesses would be more severe. Our findings support the idea that airborne infectious particles could play an important role in the spread of influenza.

Aerosol Transmission of Infectious Disease

“…92 Although there has been debate about whether influenza is transmitted through the airborne route, it is clearly transmitted through aerosols. Specifically, virus is emitted in aerosols from infectious people, 12 virus is present in the air around infectious people, 9,93 and infection has been demonstrated in human subjects subsequent to virus inhalation and intranasal instillation, 94,95 which are strong, moderate, and strong levels of evidence for conditions 1 to 3, respectively (Table 2). Seasonal influenza is a risk group 2 organism; novel influenza is in risk group 3.…”

“…[9][10][11][12] The range of particle sizes in an infectious aerosol depends on a number of factors including, but not limited to, the mechanism of aerosol generation and the liquid content and viscosity of the aerosolized fluid. 13 The liquid content of the particle influences the extent to which the particle size reduces with evaporation, although evaporation occurs rapidly, within a second of aerosol generation.…”

Widespread Virus Replication in Alveoli Drives Acute Respiratory Distress Syndrome in Aerosolized H5N1 Influenza Infection of Macaques

“…Sneezing and coughing in H5N1-infected poultry are reported infrequently as affected animals are typically found comatose or dead with few clinical signs (48). This suggests that respiratory-derived aerosols are an uncommon source of H5N1 virus from infected birds, in contrast to human-to-human transmission of seasonal influenza viruses (49, 50). This may account for the rarity of human infections despite widespread exposure to infected poultry in affected countries (51, 52).…”

Viable influenza A virus in airborne particles expelled during coughs versus exhalations

“…Cough‐ and exhalation‐generated aerosols were collected using an aerosol particle collection system (Figure 1) similar to that described previously 24. An ultrasonic spirometer (Easy One, NDD Medical Technologies) measured the volume and flow rate of each cough, and a modified 10‐liter piston‐style mechanical spirometer (SensorMedics model 762609) served as an accumulation chamber for the cough and exhalation aerosols.…”

“…Influenza virus RNA also has been found in aerosol particles collected directly from infected patients while they were coughing and breathing 17, 18, 19, 20, 21, 22, 23. Six studies have demonstrated that influenza patients expel airborne particles containing viable virus 13, 18, 19, 21, 24, 25. Pantelic et al .…”