False-Negative Rate and Recovery Efficiency Performance of a Validated Sponge Wipe Sampling Method

Abstract

Recovery of spores from environmental surfaces varies due to sampling and analysis methods, spore size and characteristics, surface materials, and environmental conditions. Tests were performed to evaluate a new, validated sponge wipe method using Bacillus atrophaeus spores. Testing evaluated the effects of spore concentration and surface material on recovery efficiency (RE), false-negative rate (FNR), limit of detection (LOD), and their uncertainties. Ceramic tile and stainless steel had the highest mean RE values (48.9 and 48.1%, respectively). Faux leather, vinyl tile, and painted wood had mean RE values of 30.3, 25.6, and 25.5, respectively, while plastic had the lowest mean RE (9.8%). Results show roughly linear dependences of RE and FNR on surface roughness, with smoother surfaces resulting in higher mean REs and lower FNRs. REs were not influenced by the low spore concentrations tested ( -an integrated network of state and local public health, federal, military, and international laboratories that can respond to bioterrorism, chemical terrorism, and other public health emergencies. However, results from surface samples were inconsistent. In some cases, contamination at a given location within a facility was not detected with initial samples, and subsequent samples were required to detect the contamination (19). A Government Accountability Office (GAO) investigation following the 2001 anthrax incident concluded that validated sampling methods and statistical sampling designs were needed to provide confidence that there is no contamination when all sample results are negative (17, 18). This conclusion strongly reinforces the need for validated sampling methods to effectively respond to biothreats and ensure public safety.Following the 2001 anthrax incident, several research teams developed and investigated (in laboratory studies) the performance of sampling methods using swab, wipe, and vacuum collection devices for Bacillus anthracis or surrogate contaminants on different surfaces (1,2,3,4,5,6,7,13,14,15,16,22,23,25,28,34,38,40,44,45). In addition, the CDC has conducted formal validation studies on two methods for sampling nonporous surfaces: macrofoam swabs (23) and cellulose sponge wipes (39).A review of the cited laboratory studies identified numerous gaps in the data on method performance (30). For example, none of the studies quantified the false-negative rate (FNR) for the sampling and analysis methods investigated. The term "false negative" refers to a failure to detect contamination from a sample collected at a contaminated location. A false negative can occur because of inefficiencies (i.e., biases) and uncertainties (i.e., imprecision) at any step of the sampling and analysis process (sample collection, storage/transportation, processing/extraction, and analytical). False negatives can occur during preliminary screening or characterization sampling at low contamination levels and during clearance sampling following the decontamination process. A better understanding of FNRs and how they are infl...

Evaluating the long‐term persistence of Bacillus spores on common surfaces

“…Although the efficiency of the recovery by wipe methods similar to the method used in this study has been well investigated by other researchers, it is variable as a function of initial inoculum dosage, surface type, humidity and time (GAO 2005, Brown et al ., 2007; Estill et al ., 2009; Rose et al ., 2011; Krauter et al . 2012, Herzog et al . 2012).…”

Extraction of Aerosol-Deposited Yersinia pestis from Indoor Surfaces To Determine Bacterial Environmental Decay

“…There are several previous studies that have primarily evaluated sampling efficiency and losses, with some studies providing bacterial surface decay information (29)(30)(31)(32)(33)(34)(35). However, most of these studies utilized liquid-deposited agent and surrogates rather than the authentic agent.…”

“…Tween 80 (0.05% in PBS) was selected as the detergent in the extraction buffer because it posed a reduced risk of cell membrane permeabilization and resulted in less foam than Triton X-100 following agitation (30,33,34). Furthermore, it was determined that a combination of sonication and vortexing would be required to efficiently remove cells from coupon surfaces, particularly carpet (29,30).…”

Evaluation of standardized sample collection, packaging, and decontamination procedures to assess cross-contamination potential duringBacillus anthracisincident response operations

“…The area that received tracer powder was considerably (3.7 times) larger than the area designated for sampling in order to model sample collection in the hot zone, where contaminants are not visible to the sampler and thus may extend beyond the sample collection template. Surface samples were collected with 3M Sponge-Sticks using the procedures described previously [13,14,18] (Figure 2). Video and photography under visible or long-wave ultraviolet light were used to document procedural steps in which gloves came in contact with contaminated surfaces and to assess contaminant (tracer powder) transfer following execution of each sampling procedure.…”

“…This inoculation method is similar to those described previously. [14,18] The targeted recovery from positive controls was 2 × 10 5 and 1 × 10 7 CFU for liquid and dry inoculums, respectively.…”