A systemwide analysis of COVID-19 retesting data at University of Pennsylvania Medical Center found patients generally tested positive for three weeks, the Pittsburgh-based health system said Aug. 10.
Researchers analyzed the results of more than 30,000 nucleic acid polymerase chain reaction COVID-19 tests performed between March 3 and May 3 across the system's 40 hospitals and 700 physician offices. Of these tests, 485 were repeated.
Of 74 patients who initially tested positive and were retested, about half still were positive. The median time between the first test and a repeat positive was 18 days, while the median time for a negative result upon retesting was 23 days. Based on this finding, researchers said PCR tests may remain positive for about 21 days.
Another 418 patients initially tested negative and were retested. Of these, 96.4 percent were still negative after the second test. Only 15 patients first tested negative and then positive.
Researchers said the data was not collected through a formal clinical trial process. Testing differed based on clinician discretion, so researchers could not calculate a true false-positive rate.
The research was published Aug. 10 in Infection Control & Hospital Epidemiology.
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