Upsurge of human rhinovirus infection followed by a delayed seasonal respiratory syncytial virus infection in Thai children during the coronavirus pandemic

Background Respiratory syncytial virus (RSV) and human rhinovirus (HRV) commonly cause influenza-like illness in young children. The global coronavirus pandemic beginning in 2020 altered the seasonality and prevalence of these respiratory infections in Thailand. We aimed to characterize the upsurge of HRV and the subsequent RSV infection observed among young children who sought medical care at a hospital in Bangkok. Methods From July to December 2020, nasopharyngeal swabs from children <= 5 years of age presented with influenza-like illness were tested for RSV and HRV using reverse-transcription polymerase chain reaction. Positive samples were Sanger sequenced. Genotyping was performed using sequence and phylogenetic analysis. Results Upsurge of HRV infection began in July and was subsequently replaced by a surge of RSV infection from September onward. In 6 months, HRV was detected in 27.5% (158/574) of the samples, of which 44% (69/158) were HRV-A, 7% (11/158) were HRV-B, and 36% (57/158) were HRV-C. Meanwhile, RSV was detected in 40.4% (232/574) of the samples, of which 78% (181/232) were RSV-A and 6% (14/232) were RSV-B. RSV peaked in October 2020, approximately 2 months later than typically seen in previous years. All RSV-A were of subgenotype ON1. Codetection of HRV and RSV was found in 5.1% (29/574). Conclusions HRV and RSV infection among young children coincided with relaxed local coronavirus public health measures, including the return to in-class schooling. The delayed RSV season in 2020 was predominantly associated with RSV-A.