Swab Protocol for Rapid Laboratory Diagnosis of Cutaneous Anthrax

Abstract

The clinical laboratory diagnosis of cutaneous anthrax is generally established by conventional microbiological methods, such as culture and directly straining smears of clinical specimens. However, these methods rely on recovery of viable Bacillus anthracis cells from swabs of cutaneous lesions and often yield negative results. This study developed a rapid protocol for detection of B. anthracis on clinical swabs. Three types of swabs, flocked-nylon, rayon, and polyester, were evaluated by 3 extraction methods, the swab extraction tube system (SETS), sonication, and vortex. Swabs were spiked with virulent B. anthracis cells, and the methods were compared for their efficiency over time by culture and real-time PCR. Viability testing indicated that the SETS yielded greater recovery of B. anthracis from 1-day-old swabs; however, reduced viability was consistent for the 3 extraction methods after 7 days and nonviability was consistent by 28 days. Real-time PCR analysis showed that the PCR amplification was not impacted by time for any swab extraction method and that the SETS method provided the lowest limit of detection. When evaluated using lesion swabs from cutaneous anthrax outbreaks, the SETS yielded culture-negative, PCR-positive results. This study demonstrated that swab extraction methods differ in their efficiency of recovery of viable B. anthracis cells. Furthermore, the results indicated that culture is not reliable for isolation of B. anthracis from swabs at >7 days. Thus, we recommend the use of the SETS method with subsequent testing by culture and real-time PCR for diagnosis of cutaneous anthrax from clinical swabs of cutaneous lesions.

Investigation and source-tracing of an anthrax outbreak in Gansu Province, China

“…Human are usually infected by contact with infected animals or contaminated animal products. Depending on the route of infection, there are three primary forms of anthrax in humans: inhalational, gastrointestinal and cutaneous [ 1 ]. Approximately 95% of infections are cutaneous, which is mainly caused by the handling of infected animal carcasses or the products of diseased animals [ 2 , 3 ].…”

Detection of Bacillus anthracis in animal tissues using InBios active anthrax detect rapid test lateral flow immunoassay

“…The supernatant was syringe-filter sterilized and used for testing. Swabs tested in ZSAL were processed using the swab extraction tube system (SETS) (Roche Applied Science, Indianapolis, IN) as previously described (Dauphin et al 2012). An aliquot of the resulting liquid was used for testing.…”

Cutaneous Hematopathology

“…The bacteria grow readily in culture media, but the organisms may not be identifi ed correctly if the laboratory is not alerted to the suspicion of anthrax. Confi rmatory cultures, serologic assays, and polymerase chain reaction (PCR) testing are available through the public health network (Dauphin et al 2012 ).…”