Comparison of Swab Sampling Methods for Norovirus Recovery on Surfaces

Human noroviruses (HuNoVs) can be easily transferred by the contacts of humans or fomites. Swab sampling methods are widely used for recovering HuNoVs from small surfaces of various fomites or hard-to-reach locations and swab sampling conditions are important for the accurate detection of HuNoVs, which have a low infectious dose and relatively long persistence under a range of environmental conditions. Therefore, to determine the suitable swab sampling method for recovering HuNoVs from various surfaces, we evaluated combinations of four swab materials (cotton, microdenier polyester [a type of microfiber], polyurethane foam, and rayon) and three elution buffer solutions (phosphate-buffered saline [PBS], PBS with 0.2% Tween-80, and 3% beef extract-50mM glycine [pH 9.5]). First, we inoculated HuNoVs or murine noroviruses (MuNoVs), the surrogate of HuNoVs, onto test coupons (10x10cm) consisting of three common surface materials (high-density polyethylene, stainless steel, and wood). Coupons were swabbed using a combination of each swab material and elution buffer, and the viral recovery was measured by real-time reverse transcription quantitative polymerase chain reaction (RT-qPCR) or plaque assay. By RT-qPCR, we confirmed that the cotton swab-PBS and microdenier polyester-PBS combinations had recovery efficiencies greater than 80% for viruses on plastic and stainless steel surfaces. The cotton swab-PBS combination had the highest recovery efficiency on all surface materials via the plaque assay. Therefore, a cotton or a microdenier polyester swab with PBS could be a useful method for sampling HuNoVs on various surfaces.