Environmental Health, Environmental Justice
Influenza Virus in Respiratory droplets from Humans with Community-Acquired Infection
(UMD, A. James Clark School of Engineering, Chemical and Biomolecular Engineering Doctoral Student )
This report describes a study of the characterization of respiratory droplets collected from infected individuals. We screened volunteers for the influenza infection and recruited persons meeting the following criteria: either a positive rapid test, or fever 37.8°C plus cough or sore throat, and were screened within the first three days of onset of symptoms. We collected exhaled breath samples, using the G-II bioaerosols sampler, nasopharyngeal (NP) swabs, and questionnaires from each subject. Each NP swab and fine (<5μm) aerosol sample were assayed by culture passage and fluorescent focus assay on MDCK cells. All samples were quantified by RTqPCR. Of the 178 person-illnesses studied, 86 were H3N2, 3 pdmH1, 64 influenza B, and 5 were culture positive but negative for influenza by PCR and focus assay, 1 unsubtypable influenza A, 3 dual infection (H3 & pdmH1, H3 & B, pdmH1 &B), 16 negative for laboratory evidence of infection (total of 157 person-illness episodes of proven influenza infection). We obtained valid culture results (passage and/or focus assay) from 228 NP swabs and 215 fine aerosol samples including all subjects; 82% of NP swabs and 46% of fine aerosol samples were positive for influenza. We detected influenza virus by RTqPCR in 46% of the coarse and 66% of fine aerosol fraction samples including all subjects. The geometric mean number of viral RNA copies in coarse (3.8, 95%CI 0.5-29) and fine (44, 95%CI 17-109). We observed weak correlations of cough with PCR detected virus particle numbers in fine (r=0.4, p<0.05) and coarse (r=0.3, p<0.05) aerosols. Our finding of culturable virus in a large proportion of aerosol samples demonstrates that influenza patients shed not merely RNA but infectious virus into airborne droplets, contributing to literature that airborne transmission via fine aerosols is biologically plausible and is likely a major route of transmission of influenza virus.