Association between time of onset and Omicron BA.2 RNA clearance time in children: a retrospective cohort study.

Background: The association between the time of onset [time from the date of detection of a positive real-time reverse-transcription polymerase chain reaction (RT-PCR) to the date of detection of a positive RT-PCR in the first child] and viral RNA clearance time (time from first positive RT-PCR to two consecutive negative RT-PCR) remains unclear. Our study aimed to evaluate their association. That can provide a reference for the number of nucleic acid tests.

Methods: We conducted a retrospective analysis of children diagnosed with Omicron BA.2 infection at Fujian Medical University Affiliated First Quanzhou Hospital between March 14, 2022 (date the first child in the outbreak was found positive for RT-PCR) and April 9, 2022 (date the last child was found positive for RT-PCR). We used the electronic medical record to extract demographic data, symptoms, radiology and laboratory findings, treatments, and viral RNA clearance time. The 282 children were divided equally into 3 groups according to the time of onset. We calculated the factors affecting viral RNA clearance time by univariate and multivariate analysis. We used the generalized additive model to investigate the relationship between the time of onset and viral RNA clearance time.

Results: 46.45% of children were female. Fever (62.06%) and cough (15.60%) were the dominant onset symptoms. We found no serious cases and all children were cured. The median time to viral RNA clearance was 14 days (IQR 12-17 days), with a range of 5 to 35 days. After adjustment for potential confounders, the viral RNA clearance time was reduced by 2.45 (95% CI: 0.85, 4.04) days in the 7-10 days group and by 4.62 (95% CI: 2.38, 6.14) days in > 10 days group compared to the ≤6 days group. There was a non-linear association between the time of onset and viral RNA clearance time.

Conclusions: Time of onset was non-linearly associated with Omicron BA.2 RNA clearance time. During the first 10 days of the outbreak, viral RNA clearance time decreased with increasing onset date. After 10 days of the outbreak, viral RNA clearance time did not decrease with increasing onset date.