All respirators, certified under Title 42, Code of Federal Regulations, Part 84, can be used by health-care workers for protection against Mycobacterium tuberculosis (Mtb). Questions have been raised regarding the possibility of the respirator becoming contaminated with Mtb or other organisms due to reuse, handling, and storage in plastic bags. This study was conducted to: (1) determine whether, and for how long, avirulent Mtb (strain H37Ra) survives on respirator material, and (2) measure levels of contamination (assess contamination by environmental bacteria and fungi due to storage in airtight bags) potentially spread to the respirator's interior surface due to normal mechanical handling (removal and re-insertion of the respirator into air-tight bag). Six models of filtering facepiece respirators were challenged with a concentration of 10^5 to 10^6 colony forming units (CFUs) H37Ra per liter of air in a steady flow system. Respirator interior and exterior surfaces were swab sampled on day -1 (prior to exposure), 0 (day of exposure), 1, 3, 7, 10, 14, 21, and 28. Between samplings, each respirator was sotred at room temperature in a Zip-lock bag. Seven days after exposure the number of viable organisms decreased from a mean range of 27 to 131 colony forming units per square centimeter (CFU/cm2) to zero CFU/cm2 on the exterior of the different respirator models. While several respirators had interior contamination immediately following challenge, no transfer of exterior H37Ra was observed. Some colony growth was recoverable from day 14 to 28 indicating there was some incidental contamination with environmental bacteria to the interior of the respirator after repeated handling and storage.
Barbara Johnson, U.S. Army Dugway Proving Ground, Dugway, Utah