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S-29A8-3 Background/Aims: The scientific literature on influenza transmission is lacking in data on the particle size, infectiousness, and quantity of viral particles released by infected persons. These data are necessary to understand the transmission pathways of influenza and are essential for assessing risk, providing interventions, and minimizing public fear. Methods: We characterized exhaled breath and cough aerosols from influenza patients using molecular and viral culture methods during seasonal influenza in Hong Kong 2007, Massachusetts 2008, and 2009. Using filters or a novel impaction system to collect exhaled virus aerosols, we estimated virus generation rates during tidal breathing and coughing. We measured particle concentrations and size distributions with an optical particle counter. During the third season we measured the effect of surgical masks on virus concentrations in fine (0.05–<5 um) and coarse (≥5 um) particles as well as virus culturability from fine particles. Results: We recruited 77 subjects with laboratory-confirmed influenza during the 3 seasons. We measured influenza RNA in 13%–33% of tidal breath samples and in 66% of cough samples. Over 87% of exhaled particles collected were less than 1 μm. Surgical masks reduced viral RNA copies in the coarse fraction from 1000 per 30 minutes to 2.6 per 30 minutes and in the fine-particle fraction from 5600 per 30 minutes to 1200 per 30 minutes. Overall, masks produced a 5.2-fold reduction in viral aerosol shedding. Samples from the 2 subjects with the highest influenza RNA copy numbers were culture positive. Conclusion: Results from these studies show that influenza virus is present in fine particles generated during tidal breathing and coughing. These results and the presence of culturable virus in fine-particle aerosols support the hypothesis that the airborne route may play a role in influenza transmission. Data from 1 study suggest that surgical masks worn by patients can moderately reduce generation of virus containing aerosols and supports Center for Disease Control recommendations.
Fabian et al. (2010) studied this question.