Detection of respiratory viruses and efficacy of face masks in reducing viral release in human exhaled breath

Abstract

Background: Respiratory viruses are associated with considerable morbidity and mortality globally. They have been detected from infected patients while breathing, speaking and coughing, but there is little data on the efficacy of facemasks to filter respiratory viruses causing common acute respiratory illnesses (ARI) as a source control to prevent transmission. We aimed to examine exhaled breath virus generation rate of different respiratory viruses, and to determine the potential benefits of facemasks to prevent respiratory virus transmission. Methods: We recruited patients ≥11 years old with ARI within 72 hours of symptom onset from an outpatient clinic in Hong Kong, and collected their nose swabs, throat swabs and exhaled breath particles. Exhaled breath was collected by a bioaerosol collecting device (G-II) which fractionated the exhaled breath into either large droplets (≥5µm) or small aerosols (<5µm). Patients were randomly allocated to wear or not to wear a surgical mask for the first 30-minute collection, and then invited to provide a second collection of the alternate type. The viral aetiology of the illness was determined by testing nose swabs with the xTAG Respiratory Viral Panel, and in those identified with a viral infection, the quantity of viral RNA specific to the identified virus was determined by RT-PCR in nose/ throat swabs and the two exhaled breath fractions. The probability of respiratory virus detection in exhaled breath was compared between patients with or without wearing facemasks. Results: 303 exhaled breath samples were collected from 256 patients, including 151 samples collected without and 152 samples with wearing a surgical mask. 153/256 (60%) patients were identified with respiratory virus infection by the xTAG, with most infections being enterovirus/ rhinovirus (25%), influenza virus (19%) and coronaviruses (9%). Quantification of viral RNA in exhaled breath samples is on-going. So far, respiratory virus RNA was detected in 20/152 (10%) exhaled breath samples - in aerosols 10/77 (13%) in control and 5/75 (7%) in mask group, and in droplets 5/77 (6%) in control and 0/75 (0%) in mask group. Influenza A and B viruses, RSV and human metapneumovirus (hMPV) were detected in aerosols, while only influenza A and B virus were detected in droplets in exhaled breath. Conclusions: Our study is the largest to date to examine release of respiratory viruses in exhaled breath, and makes an important contribution to our understanding of the infectiousness of different respiratory viruses in respiratory droplets and the efficacy of surgical facemasks in preventing respiratory virus transmission.