Controlled human influenza infection reveals heterogeneous expulsion of infectious virus into air

Influenza virus is transmitted via respiratory expulsions, but detecting infectious virus in expulsions is challenging. Here, we describe quantification and genotyping of infectious virus in respiratory particles using a modular influenza sampling tunnel (MIST). The particles deposit on cell monolayers, enabling culture, quantification, and sequencing of viruses. Concomitantly, water-sensitive paper and fine particle samplers yield respiratory particle counts over a broad size range. Using the MIST, we captured infectious virus from humans experimentally infected with the influenza virus on multiple days post-inoculation. The recovered respiratory particles varied in quantity over three orders of magnitude and contained viral variants also detected in samples from infected individuals. Expulsion of infectious virus was associated with infectious viral load in saliva and nasopharyngeal swabs and with clinical symptoms. These data reveal maintenance of viral diversity in expelled aerosols and suggest heterogeneity among individuals in the magnitude of infectious expulsions, impacting forward transmission potential.