Survival of mycobacteria on N95 personal respirators.
OBJECTIVE
The overall aim of this study was to investigate the survival and possible growth of Mycobacterium tuberculosis simulant bacteria on respirator filters.


METHODS
Mycobacterium smegmatis was used as a biochemical simulant for M tuberculosis. Bacterial survival was tested on National Institute for Occupational Safety and Health-certified N95 respirators from three manufacturers. The first experiments simulated one-time respirator use and subsequent storage for 1 to 9 days under ideal conditions for the growth of mycobacteria: 37 degrees C and 85% relative humidity. The bacteria were loaded on the respirator filters under three different nutritional conditions: in the absence of nutrients; in the presence of human saliva (simulating conditions when the respirator is worn); and in the presence of nutrient broth (for ideal growth potential). The subsequent experiments simulated respirator wear for 2 hours under medium work-load conditions at a breathing rate of 56 L/min.


RESULTS
It was found that M smegmatis did not grow on the tested respirators, even when the respirators were stored at temperature, humidity, and nutrition conditions most favorable for microbial growth. However, these bacteria could survive on respirators for up to 3 days during storage. The culturability of M smegmatis was not affected by airflow that simulated the breathing rate associated with medium work-load conditions for 2 hours.


CONCLUSIONS
This study shows that M tuberculosis surrogate bacteria collected on a respirator are not able to grow and are able to survive only in ideal (ie, not clinically relevant) conditions. Based on these experiments, we conclude that M tuberculosis is unlikely ever to become an infectious problem in the air again, once it is removed by a respirator.
Reponen
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TA
Aerosol Research and Exposure Assessment Laboratory, Department of Environmental Health, University of Cincinnati, Ohio 45267-0056, USA.
Wang
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Willeke
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Grinshpun
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D015169:Colony Count, Microbial; D004866:Equipment Contamination; D005374:Filtration; D006801:Humans; D020102:Mycobacterium smegmatis / Q000502:physiology*; D009169:Mycobacterium tuberculosis / Q000502:physiology*; D014376:Tuberculosis / Q000517:prevention & control; D012122:Ventilators, Mechanical / Q000382:microbiology*