Unexpected peak of bronchiolitis requiring oxygen therapy in February 2020: Could an undetected SARS-CoV2-RSV co-infection be the cause?

Respiratory syncytial virus (RSV) infection is the leading cause of bronchiolitis among infants <12 months old. It is widely known that coinfections between RSV and other viruses can worsen the clinical picture of affected patients. To evaluate the severity of clinical pictures of bronchiolitis in the 2019-2020 winter season, we performed a retrospective study of our third-level Pediatric Emergency Department (ED) admission charts. From February 2 to March 9, 2020 (start date of the Italian lockdown), we observed a peak of patients with a clinical picture of bronchiolitis requiring oxygen therapy of 55.1%, compared with 18% and 14.5% during the same period in 2017-2018 and 2018-2019, respectively (p<0.0001), without other clinically significant differences between the groups. Several authors hypothesized that SARS-CoV2 was present in northern Italy some weeks be-fore the first confirmed case. We suggest that one of the causes of this unexpected severe bronchiolitis peak may be a SARS-CoV2 - RSV coinfection in a period when SARS-CoV2 was already circulating in north-ern Italy. Given the lack of real-time polymerase chain reaction (RT-PCR) tests for SARS-CoV2 at that time, our suggestion remains a hypothesis.