Influenza virus in human exhaled breath

Abstract

Background: Recent studies suggest that humans exhale fine particles during tidal breathing but little is known about where the particles are generated or their role in infection transmission. We conducted a study of influenza infected patients to characterize particle and influenza virus concentrations in their exhaled breath. Methods: We recruited patients with influenza-like illness presenting for medical care at three clinics in Hong Kong, China. We collected two nasal swabs per subject, one for rapid testing and a second one for analysis via quantitative PCR (qPCR). Patients breathed with a steady regular pattern through a mouthpiece supplied with HEPA filtered air. Exhaled breath flowed through a 22 mm diameter and 40 cm long tube to an Exhalair (Pulmatrix, Inc, Lexington, MA), which monitored flow rate, and counted particles between 0.3 and 5 um in diameter using an optical particle counter. After three minutes of particle counting, we collected exhaled breath particles by sampling for 20 minutes on Teflon filters. We assayed each filter for influenza A and B using qPCR. Results: Thirteen of the 51 screened patients tested positive for influenza using the QuickVue rapid test (7 for influenza B, 6 for influenza A). Twelve rapid test positive patients completed the exhaled breath test (7 influenza B subjects and 5 influenza A subjects) and we recovered influenza virus in the exhaled breath of 4 (25%) subjects. Three (60%) of the five patients with influenza A infection and one (14%) of the seven with influenza B infection had detectable influenza virus in their exhaled breath. Exhaled breath virus concentrations ranged between 21 and 312 virus copies per sample, corresponding to a generation rate between 1 and 16 virus particles per minute. Preliminary particle data analysis indicated that 50% of subjects exhaled more than 500 particles per liter of air, a suggested threshold for identification of high particle producers. Conclusions: We recovered influenza virus from the exhaled breath of 4 out of 12 influenza patients, three of whom tested positive for influenza A. The results provide evidence that influenza virus is contained in fine particles generated during tidal breathing.