Earlier this summer the Allegheny County Health Department recommended that people who were returning from out-of-state travel should quarantine for two weeks, unless they could get two consecutive coronavirus tests that were both negative.
The recommendation was then scaled back to just one test due to a dearth of availability, and based on findings from a new UPMC study, it might have been the right call.
Researchers looked at the test results of nearly 500 patients who received two COVID-19 tests at the medical system. Of the 418 who initially tested negative, only 15 later tested positive. For the handful of patients in the analysis who did go from negative to positive, the median time between tests was eight days.
“Testing in general in the United States, it’s hard to come by,’” said Dr. Amy Kennedy, the study’s lead author. “Testing capacity is limited. Not everyone who wants a test can get one. And so we have to be judicious about who we use them.”
UPMC uses a nucleic acid polymerase chain reaction (PCR) test which it developed earlier this year. Samples are collected from patients via nasal swabs. The test was validated under the Clinical Laboratory Improvement Amendments program, which operates under the auspices of the Centers for Medicare and Medicaid Services.
Most UPMC patients are not retested for COVID-19. Therefore, researchers were unable to calculate a reliable false negative rate for the study’s findings.
Kennedy says there is still a lot about COVID-19 that’s not understood and that more research needs to be done. For example, why do some people test positive after testing negative?
“Who are those patients that test positive [after testing negative,]” she said. “Can we think about more clinical predictions? Is there a certain reason some people end up being positive later?”
While tests will produce false negatives, it’s possible that some patients caught the virus after their initial test. Figuring out if these negative results are real will help clinicians and researchers assess the consistency of test results.
Another interesting finding is that it took about three weeks for the 74 patients who tested positive for COVID-19 with their first test to test negative. However, patients weren’t contagious the entire time.
“Just having this virus in your nose does not mean that you have a high enough level of it to cause anyone else to get sick,” said Kennedy.
The findings were published in the journal of Infection Control & Hospital Epidemiology.
