A new study shows it takes roughly a month to completely clear the coronavirus from your body. To be safe, COVID-19 patients should be retested after four weeks or more to be certain the virus isn't still active, Italian researchers say. Whether you are still infectious during the month after you are diagnosed is a roll of the dice: The test used in the study, an RT-PCR nasal swab, had a 20% false-negative rate. That means one in five results that are negative for COVID-19 are wrong and patients can still sicken others.