Evaluation of Surface Sampling Performance of Four Commercially Available Swab Materials on Human Norovirus GII.4

Introduction: A swab rinse method is widely used to determine contamination levels of viruses on environmental surfaces. However, most of these methods have not been evaluated and the sampling performance remains unknown.

Purpose: We evaluated the sampling performance of four different swab materials (cotton, rayon, polyester and macrofoam) on a stainless steel surface under variable test conditions.

Methods: A clarified human GII.4 norovirus (GII.4 NoV) stool suspension (10^7.0 RNA copies/ml) was spread on stainless steel coupons, dried out at RT, and swabbed with each swab material. Different drying times (1, 8, 24, and 48 hours) and coupon size (4, 9, 16, and 25 inches²) were tested. Recovered GII.4 NoV was quantified by real time RT-PCR.

Results: The effect of drying time or surface area on sampling performance varied significantly by swab type (P <0.001).  When GII.4 NoV RNA (10^5.1 RNA copies) were seeded on coupons of 9 and 25 inches² and sampled after 8 and 48 hours of drying, four swab materials recovered GII.4 NoV (range 1.8 to 8.6%) from 9 inches² coupons. However, for the 25 inches²coupons, only macrofoam swabs were able to recover the virus (recovery ≥2.1 %). 

Significance: In conclusion, macrofoam swabs showed superior sampling performance compared to cotton, rayon, and polyester swab materials for the recovery of GII.4 NoV from a stainless steel surface. In addition, the ability of macrofoam to recover virus from 25 inches² surface areas, makes it a promising tool for the detecting of environmental reservoirs in high-risk NoV settings such as restaurants, hospitals, nursing homes and cruise ships.