Comparison of false‐negative rates and limits of detection following macrofoam‐swab sampling of Bacillus anthracis surrogates via Rapid Viability PCR and plate culture

Aims We evaluated the effects of Bacillus anthracis surrogates, low surface concentrations, surface materials and assay methods on false‐negative rate (FNR) and limit of detection (LOD95) for recovering Bacillus spores using a macrofoam‐swab sampling procedure. Methods and Results Bacillus anthracis Sterne or Bacillus atrophaeus Nakamura spores were deposited over a range of low target concentrations (2–500 per coupon) onto glass, stainless steel, vinyl tile and plastic. Samples were assayed using a modified Rapid Viability‐PCR (mRV‐PCR) method and the traditional plate culture method to obtain FNR and LOD95 results. Conclusions Mean FNRs tended to be lower for mRV‐PCR compared to culturing, and increased as spore concentration decreased for all surface materials. Surface material, but not B. anthracis surrogate, influenced FNRs with the mRV‐PCR method. The mRV‐PCR LOD95 was lowest for glass and highest for vinyl tile. LOD95 values overall were lower for mRV‐PCR than for the culture method. Significance and Impact of Study This study adds to the limited data on FNR and LOD95 for mRV‐PCR and culturing methods with low concentrations of B. anthracis sampled from various surface materials by the CDC macrofoam‐swab method. These are key inputs for planning characterization and clearance studies for low contamination levels of B. anthracis.