Introduction: Respiratory infection in particular community acquired pneumonia (CAP) in children is a major disease that ranks high in outpatient and inpatient cases. The causes of CAP vary depending on the individual susceptibility, epidemiological characteristics of the community, and season. We performed this study to establish nationwide survillance network system and identify the causative agents for CAP and antibiotics resistance in Korean children with CAP.. Methods: The monitoring network was composed of the 28 secondary and tertiary medical institutions. Upper and lower respiratory samples were assayed using culture or Polymerase chaini reaction (PCR) from Aug 2018 to May 2020. Results: A total of 1023 cases were registered in patients with CAP, and 264 cases (25.8%) were isolated by culture, S. aureus 131 cases (12.8%), S. pneumoniae 92 cases (9%), H. influenzae 20 cases (2%). PCR of atypical pneumonia pathogen revealed 422 cases of M. pneumoniae (41.3%). Respiratory virus showed positive rates in 65.7% by multiplex PCR test and of them, human rhinovirus was most highest with 312 cases (30.5%). The proportion of mixed infection was 49.2%. The rate of antibiotics resistance showed similar results as previous reports. Conclusion: It will identify the pathogens that cause respiratory infections, and analyze the current status of antibiotic resistance to provide scientific evidence for management policies of domestic respiratory infection. Also, in preparation for the new epidemic, including COVID19, monitoring of respiratory infections in children and adolescents, has become more important, and research should be continuously conducted in the future.

Background: Air pollution can be a risk factor for respiratory viral transmission and infection. The COVID-19 outbreak in 2020 may have affected ambient air pollution levels. Therefore, this study aimed to investigate air pollution levels and respiratory virus infection rates before and after the COVID-19 pandemic as well as determine relationships between these factors. Methods: The daily mean temperature and concentrations of air pollutants (PM2.5, PM10, O3, NO2, CO, and SO2) in five metropolitan cities in South Korea were collected for the months of February to May from 2015 to 2020. Results of 14 respiratory viruses isolated using polymerase chain reaction in children with upper or lower respiratory tract infections were gathered during the same period. Trends of respiratory virus infection, temperature, and air pollutant level from February to May for six years were evaluated and possible relationships between respiratory virus infections and ambient air pollutant levels were assessed. Results: Most air pollutants exhibited significantly decreasing trends in 2020 compared to the years before COVID-19. There were no differences in temperature. Adenovirus, bocavirus, metapneumovirus, parainfluenza virus 3, and rhinovirus were the most frequently detected viruses from February to May from 2015 to 2019, and infection rates dropped significantly in 2020. The concentration of ambient O3 was associated with rhinovirus infection in hospitalized children (aOR [95% CI], 1.028 [1.002, 1.055]). Conclusions: After the COVID-19 outbreak, ambient air pollution levels and respiratory virus transmission decreased in the pediatric population of South Korea.