Image: Courtesy of SureScreen Diagnostics

With reports of an incubation period of up to 14 days for COVID-19, before symptoms are shown, the chances of virus transmission within the population prove hard to contain. Molecular based tests are typically performed, as instructed by health authorities, only if the particular COVID-19 symptoms are shown or if they have arrived from a high-risk country. Therefore the patient may be carrying this virus for 14 days without being aware of it due to not showing any of the symptoms yet, hence behaving as normal in their daily life. 

An increase in molecular testing in the countries affected has caused a shortage of swabs and health authorities are already enquiring with immunoassay kit developers for an alternative.

SureScreen Diagnostic's lateral-flow COVID-19 IgG/IgM Rapid Test Cassette can detect antibodies produced by the body 3-7 days after the onset of infection. It is a qualitative membrane-based immunoassay for the detection of SARS-CoV-2 antibodies in whole blood, serum, or plasma. This test consists of two components, an IgG component and an IgM component. In the IgG component, anti-human IgG is coated in the IgG test line region. During testing, the specimen reacts with SARS-CoV-2 antigen-coated particles in the test cassette.

The mixture then migrates upward on the membrane chromatographically by capillary action and reacts with the anti-human IgG in the IgG test line region. If the specimen contains IgG antibodies to SARS-CoV-2, a coloured line will appear in the IgG test line region. In the IgM component, anti-human IgM is coated in IgM test line region. During testing, the specimen reacts with anti-human IgM. IgM antibodies to SARS-CoV-2, if present in the specimen, reacts with the anti-human IgM and the SARS-CoV-2 antigen-coated particles in the test cassette, and this complex is captured by the anti-human IgM, forming a coloured line in IgM test line region.

Therefore, if the specimen contains IgG antibodies to SARS-CoV-2, a coloured line will appear in the IgG test line region. If the specimen contains IgM antibodies to SARS-CoV-2, a coloured line will appear in the IgM test line region. If the specimen does not contain antibodies to SARS-CoV-2, no coloured line will appear in either of the test line regions, indicating a negative result. To serve as a procedural control, a coloured line will always appear in the control line region, indicating that the proper volume of specimen has been added and membrane wicking has occurred. 

Each kit box will allow 25 COVID-19 tests and each test will give a result in ten minutes. 

With the announcement by flock swab manufacturers, that they are in short supply across Europe and the US, immunoassay kits such as SureScreens test strip, that require no swabs or enclosed specialized laboratory or equipment, maybe the best method at present to manage the outbreak. 

Note: Avantor is a distributor of the product for Europe through the VWR distribution channel