Changes in Respiratory Nosocomial Microbes Before and after the Covid-19 Pandemic in South Korea

This study aimed to determine the relationship between personal hygiene and the epidemiology of infections caused by respiratory microbes. Herein, we analyzed the change in the population of respiratory microbes before and after the coronavirus disease-2019 (COVID-19) pandemic. We retrospectively analyzed the laboratory test results obtained from the examination of 307,794 sputum samples collected from 128,336 patients in seven university hospitals across Korea from January 2018 to December 2021. We also isolated and cultured 56,814 bacterial strains from samples of 52,185 patients. Compared to the pre-COVID-19 pandemic period, the number of patients whose samples were cultured for analysis of respiratory microbes, the number of positive microbial cultures, the number of respiratory samples received, and the sample positivity rate decreased by 13.5%, 7.3%, 9.5%, and 3.5%, respectively, after the pandemic. No significant difference was observed in the population of nosocomial bacteria before and after the pandemic; however, compared to that before the pandemic, the populations of Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis, the causative agents of community-acquired pneumonia, were significantly reduced by 61.4%, 56.0%, and 79.2%, respectively, after the COVID-19 pandemic. Overall, the improvement in personal hygiene management during the COVID-19 pandemic was significantly correlated with the epidemiologic changes in infections caused by respiratory microorganisms. The number of respiratory microbial infections decreased after implementing the non-pharmaceutical intervention (NPI) public health strategy. We believe this strategy is essential for controlling respiratory microbial infectious diseases in the future.