An analysis from the University of Pittsburgh (USA) has shown that COVID-19 patients maintain their positives for an average of three weeks, and that retesting in patients who were initially negative very rarely led to a positive result. In their work, published in the journal ‘Infection Control & Hospital Epidemiology’, the researchers reviewed the results of more than 30,000 COVID-19 tests on adult patients. The tests were conducted between 3 March and 3 May 2020. Of those tests, 485 were repeated at least once. Among the 74 patients who initially tested positive and were re-examined, about half were still positive and the other half were negative. The average time between an initial positive and a repeat of the positive was 18 days, while the average time between an initial positive and a negative test was 23 days, suggesting that PCR tests may remain positive to somewhere in between, around 21 days. The most common reason for retesting in someone who initially tested positive was to determine whether it was necessary to continue infection prevention protocols when the patient was discharged. Of the 418 patients who initially tested negative and re-tested, 96.4 percent were still negative when they were re-tested. Preoperative asymptomatic screening was the most common reason negative patients were retested, followed by clinical suspicion that the first test was a false negative. For the 15 patients who went from negative to positive, the average time between tests was eight days.” While our analysis cannot provide definitive clinical guidance regarding retesting for COVID-19, it does point to several interesting areas for further research, such as identifying initial false negative predictors and providing a better estimate of the time that someone who tests positive could transmit the virus to others,” explains the lead author Amy Kennedy.