RAT Reliability

Reliability of RAT tests has been questioend by the NZ Science Media Centre

The New Zealand government currently requires Covid positive cases to isolate for seven days or until their symptoms end.

The Science Media Centre spoke to two experts about transmission and the reliability of RATs; Dr Emily Harvey, Co-lead of the Contagion Network modelling programme and COVID-19 Modelling Aotearoa. Dr Anja Werno, Chief of Pathology & Clinical Microbiologist & Virologist, Canterbury Health Labs and Clinical Senior Lecturer at the University of Canterbury.

Dr Emily Harvey commented that there is a large amount of infection variability after the seven-day isolation period. International data suggests that between 10 and 25 percent of confirmed cases will still be infectious on day eight. But this also depends on what gets counted as day zero.

A positive RAT is a strong indicator that someone is still infectious. Therefore, requiring people to return a negative test at the end of their isolation period before being 'released' could help reduce infections.

RATs have a low false-positive level and a high sensitivity rate during the infectious period. They measure live virus culture compared to PCR tests that detect dead viral material over an extended time. RATs are much more preferable for an isolation release test.

Using a test-to-release could allow some people to end their isolation early.

Dr Anja Werno believes positive RATs are reliable enough to determine 'infectiousness.' Negative tests are produced when the virus load drops, and there is an effective immune response - typically 7-14 days. Everyone responds differently, but it is not unusual for cases to stay RAT positive for more than seven days.

"Another factor influencing the quality and reliability of the RAT test result is the quality of the specimen. So, ideally, if implementing a "test-to-release" the test should be done either under supervision or in an accredited facility."