Swab Sampling Method for the Detection of Human Norovirus on Surfaces

A macrofoam based sampling methodology was developed and evaluated for the detection and quantification of norovirus on environmental hard surfaces.

Human noroviruses are a leading cause of epidemic and sporadic gastroenteritis worldwide. Because most infections are either spread directly via the person-to-person route or indirectly through environmental surfaces or food, contaminated fomites and inanimate surfaces are important vehicles for the spread of the virus during norovirus outbreaks.

We developed and evaluated a protocol using macrofoam swabs for the detection and typing of human noroviruses from hard surfaces. Compared with fiber-tipped swabs or antistatic wipes, macrofoam swabs allow virus recovery (range 1.2-33.6%) from toilet seat surfaces of up to 700 cm². The protocol includes steps for the extraction of the virus from the swabs and further concentration of the viral RNA using spin columns. In total, 127 (58.5%) of 217 swab samples that had been collected from surfaces in cruise ships and long-term care facilities where norovirus gastroenteritis had been reported tested positive for GII norovirus by RT-qPCR. Of these 29 (22.8%) could be successfully genotyped. In conclusion, detection of norovirus on environmental surfaces using the protocol we developed may assist in determining the level of environmental contamination during outbreaks as well as detection of virus when clinical samples are not available; it may also facilitate monitoring of effectiveness of remediation strategies.

1. Swab Sampling in the Field

1. Wear a clean pair of gloves.
2. Measure the size of the sampling area without touching the surface using a measuring tape or ruler. Try to estimate the area as accurately as possible and fill out a report form (Supplementary Table 1).
3. Check the swab kit for possible leakages and label sample transport bags and swab kits.
4. Move the swab across the sampling area as follows: one stroke in horizontal direction, one stroke in vertical direction, and one stroke in a diagonal direction. Do not swab a surface area larger than 700 cm².
5. Place each swab into a tube and tight....

Figure 1 presents a flowchart of the swab sampling protocol. This protocol consists of four main steps; 1) sample collection, 2) sample storage and transportation, 3) viral RNA purification and concentration and 4) RT-qPCR assay and genotyping.

Figure 1: Flow chart of the final protocol for environmental surface sampling of norovirus Please click here to view a larger version o....

Noroviruses have a 50% human infectious dose between 18 and 10³ virus particles²⁰. Therefore, even low-level contamination of surfaces may pose a public health risk. Several aspects of the swab sampling protocol were evaluated including: 1) different swab materials, 2) storage condition swabs during transport, 3) viral RNA concentration, and 4) coliphage MS2 as internal extraction control.

Until recently, only the performance of swabs made from cotton, polyester, nylon and antistatic wipe) had been evaluated and proposed for field use^13,14,