Background: Bronchiolitis is the most common viral infection of the lower respiratory tract in infants under 2 years of age. The aim of this study was to analyze and compare the seasonal bronchiolitis peaks before and during the SARS-CoV-2 pandemic. Methods: Descriptive, prospective, and observational study. Patients with severe bronchiolitis admitted to the Pediatric Intensive Care Unit (PICU) of a referral tertiary hospital between September 2010 and June 2021 were included. Demographic data were collected. Viral laboratory-confirmation was carried out. Each season was analyzed and compared. The daily average temperature was collected. Results: 1116 patients were recruited, 58.2% of them males. The median age was 49 days. Respiratory syncytial virus (RSV) was isolated in 782 cases (70.1%). In April 2021, the first and only case of bronchiolitis caused by SARS-CoV-2 was identified. The pre- and post-pandemic periods were compared. There were statistically significant differences regarding: age, 47 vs. 73 days (p = 0.006), PICU and hospital length of stay (p = 0.024 and p = 0.001, respectively), and etiology (p = 0.031). The peak for bronchiolitis in 2020 was non-existent before week 52. A delayed peak was seen around week 26/2021. The mean temperature during the epidemic peak was 10ºC for the years of the last decade and is 23ºC for the present season. Conclusion: The COVID-19 pandemic outbreak has led to a clearly observable epidemiological change regarding acute bronchiolitis, which should be studied in detail. The influence of the environmental temperature does not seem to determine the viral circulation.

During the pandemic caused by the novel coronavirus (COVID-19), lung ultrasound has been used to diagnose and monitor respiratory condition. The aim of the study was to describe lung ultrasound findings in children with a COVID-19 infection. Patients younger than 18 years old and positive for COVID-19, admitted to pediatric tertiary referral hospital were included. They were divided into two groups depending on the presence of respiratory symptoms. Lung ultrasound results were categorized into four degrees according to Soldati et al. score (J Ultrasound Med 39:1–7, 2020) and it was also described the presence and type of consolidation. Sixteen patients were recruited. The median age was 11 years old (IQR 2.8–12). Four children (25%) required admission to the intensive care unit. Six patients (37.5%) presented with respiratory symptoms. Most of them showed S.score of 2 and subpleural consolidations were observed in four cases (66.6%). Ten patients (62.5%) presented with non-respiratory symptoms, lung ultrasound showed S.score from 0 to 2. Three (30%) were diagnosed of multisystem inflammatory syndrome and lung ultrasounds showed S.score of 2 with bilateral pleural effusion. Conclusions: Children with COVID-19 and respiratory symptoms mostly showed a S.score of 2 and 3 with subpleural consolidations, upon the lung ultrasound assessment. What is Known: • Lung ultrasound is a useful tool for monitoring patients with respiratory symptoms in both adults and children. Lung ultrasounds are altered in adult patients with COVID-19. What is New: • Lung ultrasound might improve COVID-19 assessment, it could be a useful tool to diagnose and monitor patients throughout the COVID-19 pandemic. Even COVID-19 patients with non-respiratory symptoms have lung alterations that are visible on lung ultrasound.