O-17 Rapid antigen tests: a screening tool for SARS-CoV-2 but not a diagnostic test
Author(s):
CNL Macpherson , N Cudjoe , N Noel , V Matthew-Belmar , B Sharma , E Chitan , TP Noel, K Yearwood
Year of Presentation:
2022
Objective: Rapid antigen tests became an important surveillance method to identify individuals who were considered to be infective to others during the COVID-19 pandemic. Negative tests facilitated entry to large events and to access academic campuses. The sensitivity and specificity of the rapid test lent credibility to their role in helping to prevent transmission.
Methods: A voluntary and free rapid antigen test was implemented as a surveillance tool for individuals accessing a campus for a tertiary educational institution in Grenada following two mass screening programs in August/September 2021. Confirmatory diagnostic PCR tests were initially used for all rapid test positives. This practice was discontinued following a 100% concordance of positive results between the tests.
Results: On suspicion of false-positive rapid tests, PCR tests were reinstituted in January 2022. Sixty-five percent of 42 rapid tests were discovered to be false-positive when using a new batch of rapid tests.
Conclusion: Two outbreaks caused by the Delta and BA. 1 clade of the Omicron variant of SARS-CoV-2 were documented in Grenada in August/September 2021 and December/February 2022, respectively. Mass screening programs, with isolation of positive cases and quarantine for contacts who were subsequently tested, were introduced. Initially, these were PCR tests, but subsequently, the rapid antigen test was used. The discovery of a large number of falsepositive rapid antigen tests reminds us that these tests are for surveillance and PCR tests remain the Gold Standard diagnostic test. All false-positive rapid test results came from a single batch of rapid antigen tests and are attributed to a manufacturing issue. Testing and subsequent isolation of positive cases and quarantine of contacts provided one of the non-pharmaceutical approaches to control COVID-19 in Grenada. Confidence in positive results, due to their implications remains paramount.