Measurements of Airborne Influenza Virus in Aerosol Particles from Human Coughs

Abstract

Influenza is thought to be communicated from person to person by multiple pathways. However, the relative importance of different routes of influenza transmission is unclear. To better understand the potential for the airborne spread of influenza, we measured the amount and size of aerosol particles containing influenza virus that were produced by coughing. Subjects were recruited from patients presenting at a student health clinic with influenza-like symptoms. Nasopharyngeal swabs were collected from the volunteers and they were asked to cough three times into a spirometer. After each cough, the cough-generated aerosol was collected using a NIOSH two-stage bioaerosol cyclone sampler or an SKC BioSampler. The amount of influenza viral RNA contained in the samplers was analyzed using quantitative real-time reverse-transcription PCR (qPCR) targeting the matrix gene M1. For half of the subjects, viral plaque assays were performed on the nasopharyngeal swabs and cough aerosol samples to determine if viable virus was present. Fifty-eight subjects were tested, of whom 47 were positive for influenza virus by qPCR. Influenza viral RNA was detected in coughs from 38 of these subjects (81%). Thirty-five percent of the influenza RNA was contained in particles >4 µm in aerodynamic diameter, while 23% was in particles 1 to 4 µm and 42% in particles <1 µm. Viable influenza virus was detected in the cough aerosols from 2 of 21 subjects with influenza. These results show that coughing by influenza patients emits aerosol particles containing influenza virus and that much of the viral RNA is contained within particles in the respirable size range. The results support the idea that the airborne route may be a pathway for influenza transmission, especially in the immediate vicinity of an influenza patient. Further research is needed on the viability of airborne influenza viruses and the risk of transmission.

Comparison of spike and aerosol challenge tests for the recovery of viable influenza virus from non‐woven fabrics

“…Although RT‐PCR provides no indication of virus infectivity, it has been found to give a higher rate of virus detection than culture methods 17, 18, 34, 35. RT‐PCR can be used combined with culture methods to help differentiate the relative contribution to recovery efficiency by the inefficient physical removal of virus from the non‐wovens and by the natural decay of virus infectivity (e.g., desiccation).…”

“…As reviewed by Gralton et al .,16 breathing, coughing, sneezing, and talking can easily generate particles of a wide size range, and influenza virus has been detected in the particles generated by human respiratory activities 8, 17, 18. Therefore, we investigated the difference in viable influenza virus recovery from PPE after liquid suspension spike tests versus aerosol challenge tests.…”

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

“…Influenza virus RNA has been detected in respirable airborne particles collected in healthcare facilities and other locations 9, 10, 11, 12, 13, 14, 15, 16. 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.…”

“…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 .…”

Highly efficient collection of infectious pandemic influenza H1N1 virus (2009) through laminar-flow water based condensation

“…While the importance of airborne transmission relative to direct contact is still debated, substantial evidence exists that airborne viruses pose a significant risk (Killingley and Nguyen-Van-Tam 2013). Several investigators have isolated infectious (viable, "live") IFV from ultrafine aerosols produced by infected patients (Lindsley et al 2010;Milton et al 2013;Lednicky and Loeb 2013). However, virus genomic RNA (vRNA) is more frequently detected than infectious virus.…”