Table 3

Probability of viral clearance confirmation (two negative nasopharyngeal swabs) by time from diagnosis or symptom onset and first swab negative on RT-PCR for SARS-CoV-2 in a cohort of COVID-19 subjects diagnosed before 22 April 2020 and resident in Reggio Emilia province

Time to first negative fromN° of first negative testN° of first negative test with retest (and %)N° of confirmed negative test (those with a negative retest) (and %)
First positive
 10–14 days3430 (88.2)14/30 (46.7)
 15–19 days134132 (98.5)95/132 (72.0)
 20–24 days131124 (94.7)99/124 (79.8)
 25–29 days196169 (86.2)140/169 (82.8)
 30–34 days13775 (54.7)67/75 (89.3)
 >34 days7224 (33.3)21/24 (87.5)
Symptom onset
 10–14 days97 (77.8)3/7 (42.9)
 15–19 days2323 (100.0)11/23 (47.8)
 20–24 days8888 (100.0)66/88 (75.0)
 25–29 days147137 (93.2)106/137 (77.4)
 30–34 days158140 (88.6)112/140 (80.0)
 >34 days279159 (57.0)138/159 (86.8)