When comparing methods for monitoring the presence of viruses on surfaces, the entire test should be considered, i.e. swabbing of a surface and detection of the resuspension.
Because PCR (which targets viral RNA) and Immuno-Detection (which targets a viral protein) do not detect the same target, these technique should be compared using samples containing intact virus.
Hygiene monitoring tests such as COV-Hygien Xpress are designed for use on site, but intact virus is hazardous and must be handled in an appropriately equipped laboratory, which explains the current lack of true comparative data.
Studies to determine the limit of detection (LOD) on common surfaces are in progress and will be shared soon.
The swabbing step has a significant impact on the LOD because it determines the % of virus that is lifted off of the surface, the % of virus lifted onto the swab that is resuspended in the reagent, and the dilution of the virus in the resuspension buffer.
Even supposing that the % of virus lifted onto the swab and resuspended in the buffer are identical for (i) a sample tested on site with COV-Hygien Xpress and (ii) a sample sent to a laboratory for PCR testing, the viral dilutions are typically different. For PCR analysis the virus is typically resuspended in 3 mL of transport media, whereas the volume of resuspension buffer recommended for COV-Hygien Xpress is 0.45 mL.
Thus, when the complete test protocol is carried out, the virus is diluted less by the standard COV-Hygien Xpress protocol than by a standard PCR protocol.
The following two studies compared PCR to Imumuno-Detection (the technology behind COV-Hygien Xpress) in a clinical context. The comparisons were made using clinical samples to determine whether Immuno-Detection is suitable for diagnostic use in humans, and only evaluated the detection methods.
- Front. Med., 08 May 2020
- Journal of Clinical Microbiology Jun 2020, JCM.00977-20; DOI: 10.1128/JCM.00977-20
The data show that Immuno-Detection has high sensitivity, although it was not quite as sensitive as PCR in clinical samples, and that both techniques are equally specific.
Overall, both methods can be expected to have similar LODs.