Environmental sampling to ascertain the presence of Bacillus anthracis spores in buildings is an important tool for assessing risk for exposure. Similar to diagnostic testing, culture with positive identification of B. anthracis (CDC culture method) is the confirmatory test. Laboratory-based polymerase chain reaction (PCR) methods for detecting genetic material of B. anthracis can be used in preliminary assessments and as adjuncts to microbiologic methods. Although these tests are consistent with culture results, PCR methods are not approved by the Food and Drug Administration, and results should not be the basis for clinical decisions.
Rapid-assay devices that can provide results within minutes are used for onsite detection of environmental contamination. Some of these devices are PCR-based assays, and others are immune-based assays for B. anthracis. CDC has not obtained validation data for rapid-assay devices. A recent CDC evaluation of B. anthracis contamination at the Brentwood postal facility in the District of Columbia included use of one onsite PCR-based device and CDC culture method. Of 107 samples analyzed using CDC culture method and the PCR-based device, 95 (89%) were negative by both methods. Of six samples identified as positive by CDC culture method, two were positive using the PCR-based device. Of eight samples identified as positive by the PCR-based device, two were positive by CDC culture method. Although these results indicate a poor agreement between results from the onsite PCR-based device and CDC culture method, this assessment was not intended as a formal validation test because of limited capacity to implement adequate quality-control measures and the small number of B. anthracis positive samples.
The apparently poor agreement of the onsite PCR-based device could be attributed to several factors such as the concentration of spores on contaminated surfaces, sample collection and preparation procedures, sample splitting, and the methods used for removing the sample from collection material. Furthermore, PCR- or immune-based tests do not distinguish viable from nonviable spores and can produce positive scores for samples that culture methods would define as negative. As a result, these methods are not useful for evaluating the success of disinfection techniques that do not remove nonviable spores.
Public health officials are urged to understand the limitations of onsite, rapid technologies for B. anthracis before using them for public health decision making. Until validation testing is complete and guidelines for effective use are developed, PCR- or immune-based assay results for B. anthracis should not be used alone, but should be confirmed with samples analyzed by culture methods to make public health decisions. Danila, PhD, HF Hull, MD, State Epidemiologist, Minnesota Dept of Health. Div of Healthcare Quality Promotion, National Center for Infectious Diseases; and EIS officers, CDC.
Use of Onsite Technologies for Rapidly Assessing Environmental Bacillus anthracis Contamination on Surfaces in Buildings. JAMA. 2002;287(2):184. doi:10.1001/jama.287.2.184-JWR0109-3-1