Health & Environmental Research Online (HERO)


Print Feedback Export to File
2625127 
Journal Article 
Abstract 
Influenza virus aerosols in human exhaled breath: particle size, culturability, and effect of surgical masks 
Milton, DK; Fabian, MP; Angel, M; Perez, DR; Mcdevitt, J 
2010 
Yes 
American Journal of Respiratory and Critical Care Medicine
ISSN: 1073-449X
EISSN: 1535-4970 
181 
A6844 
English 
WOS:000208771005440 
is part of a larger document 3452678 Proceedings of the American Thoracic Society 2010 International Conference, May 14-19, 2010, New Orleans
RATIONALE: The CDC recommends that influenza patients don surgical masks to protect others. In support of that recommendation, a recent report suggested that surgical masks contain virus in large droplet spray. There is, however, no evidence that surgical masks capture viral aerosols (i.e. droplets less than 20 μm and their residua known as droplet nuclei). On the other hand, there is also no direct evidence that exhaled aerosols contain culturable virus likely to be infectious to humans.

METHODS: We collected exhaled particles in two size fractions (coarse ≥ 5 µm, fine 0.05 to < 5 µm) from 37 volunteers with seasonal influenza during January – March, 2009 in Lowell, MA. We measured viral particle numbers using quantitative reverse transcriptase-PCR and tested fine particles for presence of culturable virus.

RESULTS: Surgical masks reduced viral RNA copies in the coarse fraction (Figure A): 1000 (95% confidence interval 230 - 4,700) per 30 min to 2.6 (0.5 - 12). We observed a less dramatic reduction in viral copies in the fine-particle fraction (Figure B): 5600 (1700 - 19000) per 30 min without a mask and 1200 (36 - 3800) when wearing a mask. Influenza virus copy number in coarse (A) and fine (B) aerosol fractions. Influenza virus copy number in coarse (A) and fine (B) aerosol particles exhaled by patients with and without wearing of an ear-loop surgical mask. Each line represents an individual volunteer. Zero counts are represented as 0.1 on the log scale. Overall, masks produced a 5.2 (3.7 - 7.4) fold reduction in viral aerosol shedding. Virus numbers in exhaled breath declined rapidly from the first to the second day after onset of illness. Samples collected with and without surgical masks were culture positive for two subjects with the highest copy numbers.

CONCLUSIONS: These data suggest that surgical masks worn by patients can moderately reduce generation of virus containing aerosols and supports CDC recommendations. Presence of culturable virus in fine-particle aerosols supports the hypothesis that the airborne route plays a role in transmission of influenza. Presence of culturable virus in samples collected while volunteers wore surgical masks suggests that if fine particle aerosols are the major pathway of transmission, that surgical masks as source control will be of limited utility. New studies to identify the importance of the aerosol pathway for influenza transmission are needed.

*Figures in pdf 
American Thoracic Society 2010 International Conference 
New Orleans, LA 
May 14-19, 2010