Window for Detection of SARS-COV-2 Infection
SARS-COV-2 is a new virus, emergent to humans. Since its first report in December 2019, we have gained tremendous understanding of its transmission, virus replication in the human body, immune response, pathogenesis, clinical symptoms, diagnosis, and treatment.
Nandini Sethuraman concluded a most comprehensive and sound laboratory testing window with different technologies based on published studies.
The illustration clearly promotes that detection sensitivity for SARS-COV-2 antibodies or NTA varies significantly from the time the specimens are taken. Often, we have seen specimens drawn far too early (i.e., less than two weeks after the onset of symptom) for a body’s immune response to have released the minimum levels of antibodies that an antibody test would need to detect infection.
A review article suggests that over the four days of infection before the typical time of symptom onset (day five), the probability of a PCR false-negative result in an infected person was 100% on day one after infection before onset, and 68% on day four after infection before onset.2 On the day of symptom onset, the median false-negative rate was 38%. This decreased to 20% three days after symptom onset, then began to increase again, from 21% on day nine to 66% on day 21.
CTK’s OnSite COVID-19 IgG/IgM Rapid Test was evaluated by The Doherty Institute’s study, “Post-market validation of three serological assays for COVID-19,” showing a curve in IgM and IgG detection similar to the one illustrated above.3 The data showed an increase in IgM detection up to 20 days post-symptom onset, followed by a decrease, while IgG performance showed detection increase for up to 30 days.
In summary, the time of testing relative to the onset of symptoms is critical to achieve the highest detection rate for any test.
OnSite COVID-19 IgG/IgM Rapid Test Performance Over Time, after Onset of Symptoms
The OnSite COVID-19 IgG/IgM is designed to specifically detect IgG or IgM antibodies in human serum, plasma, and whole blood, as an aid in identifying individuals with an adaptive immune response to SARS-CoV-2, indicating recent or prior SARS-COV-2 infection. The result does not provide answers to whether the individual has an acute infection. A confirmative test is required to diagnose acute infection.
Both in-house and outside evaluation studies of the OnSite COVID-19 IgG/IgM Rapid Test was conducted in multiple countries, and they consistently show high antibody detection rate on specimens collected after 2-3 weeks from the first demonstration of symptoms (see table 1 below).
Table 1: Summary of results of multiple evaluation studies in different countries
These results are in agreement with USA FDA latest guidelines on the application of serological tests: identifying individuals with an adaptive immune response to SARS-CoV-2, indicating recent or prior infection.
The OnSite COVID-19 IgG/IgM Rapid Test features:
1) a low complicity test method, that can be used by health care providers with minimal training,
2) no need for instruments or electricity,
3) results in 10-15 minutes,
4) multiple specimen types, including fingertip capillary blood.
Therefore, this test is suited for the following scenarios: