782. A Comparison of Four Different Sampling Methods Used to Recover Contamination from Environmental Surfaces

Abstract

Abstract Background We hypothesized that sampling tools with the largest surface area would be the most efficient at recovering bacteria. To test this hypothesis, we evaluated four different sampling methods to see which was most effective at recovering bacteria from common environmental surfaces. Methods At UNC Medical Center, a 951 bed academic facility, we tested four collection methods: swabs, RODAC (replicate organism detection and counting) plates, Sponge Sticks with manual extraction and Sponge Sticks using extraction with the Seward Stomacher. Laminate and stainless steel surfaces (100 cm²) were used for testing. Known quantities of Staphylococcus aureus (SA) and Klebsiella pneumoniae (KP) were applied across the test surfaces, then allowed to dry prior to sampling. Swab samples were collected by rubbing a moistened swab over the test surface, followed by a dry swab. Both swab tips were broken into a tube of saline and mixed. An aliquot of each was inoculated to agar plates. Each RODAC agar plate was pressed onto a test surface. Sponge Stick samples were collected by rubbing a pre-moistened sponge over the test surface. Each sponge head was ejected into a bag containing saline. For manual agitation, each bag was kneaded by hand for 1 minute. For Stomacher method, bags were processed for 1 minute. The contents of each bag were poured into tubes, then centrifuged. The supernatant was removed from each tube. An aliquot of each was inoculated to agar plates. Plates were incubated at 35°C, then colonies were counted for each plate. Results Comparative recovery rates across surfaces, organism types and sampling methods are shown in the table. Conclusion Organism type, not sampling method, appeared to the most important factor in bacterial recovery. Recovery of SA was significantly higher than KP, likely because it was able to better withstand manipulation and the physical stress of drying on test surfaces. The sampling tool appeared to have the second largest impact. RODAC yielded the highest recovery, followed by swabs, then sponges. Knowing the variable recovery based on method, surface and organism is important for meaningful interpretation of environmental surveillance conducted during outbreak investigations or quality assurance monitoring. Disclosures William Rutala, MS, MPH, PhD, PDI (Professional Disposibles International) (Consultant) David J. Weber, MD, MPH, PDI (Consultant)