Health hazard evaluation report: HETA 2002-0109-2927, NIOSH evaluation of air sampling methodologies for Bacillus anthracis in a United States Postal Service Processing and Distribution Center, Trenton, New Jersey.
On January 16, 2002, NIOSH received a request for a health hazard evaluation (HHE) from the United States Postal Service (USPS) regarding Bacillus anthracis (B. anthracis) contamination in the Trenton Processing and Distribution Center (TPDC) located in Trenton, New Jersey. The USPS requested assistance in determining the most appropriate method(s) of air sampling for B. anthracis spores. In response to this request, NIOSH investigators conducted an evaluation of sampling methods at the TPDC on February 4-7, 2002. NIOSH investigators collected 106 surface wipe samples on the jogger/sorter, feeder, reader, and all final stacker (bin) sections of a Delivery Bar Code Sorter (DBCS), 130 general area (GA) air samples using Andersen samplers with sheep blood agar, 24 GA air samples using mixed-cellulose ester filter media, 24 GA air samples using polytetrafluoroethylene filter media, 72 GA air samples using gelatin filter media, and 6 GA air samples using a dry filter unit with polyester felt filter media. Wipe and air samples were collected before and after operating the DBCS. Operating the DBCS provided a means of re-aerosolization of spores resulting in enhanced capture potential for air sampling media. All of the wipe samples were positive for B. anthracis. The initial analysis of air samples (using 10% of the sample extract) collected before DBCS operation resulted in no detectable B. anthracis colonies (negative sample), except for some Andersen samples. All of the negative filter samples were re-analyzed using the remaining sample, which resulted in each type of filter media having one or more false negative samples. All air sample media had detectable B. anthracis colonies subsequent to DBCS operation. Based on the surface wipe and air sample data, NIOSH investigators conclude the following: (1) walking and light work may be sufficient to re-aerosolize B. anthracis spores; (2) all air sampling methods used were capable of collecting B. anthracis spores, albeit some more efficiently than others; (3) not plating the entire sample during analysis may result in false negative sample results; (4) the Andersen sampling method seems to be the most sensitive for B. anthracis spore collection; (5) because of its high flow rate the dry filter unit may have reduced the number of available spores for collection; (6) the dry filter unit may be the least sensitive when considering the volume of air passing through the sampler. Further laboratory and field evaluation of these and other methods is necessary to understand their practical uses and limitations for collection of B. anthracis in contaminated facilities.