Changes in the Distribution of Respiratory Microorganisms before and during the COVID-19 Pandemic, Daegu, Korea

Background: Acute respiratory infection (ARI) is the most common infectious disease in all ages and genders worldwide. Respiratory microorganisms such as respiratory viruses, are commonly responsible for causing ARI. COVID-19 is still prevalent in Korea. The implementation of lockdown and strict control measures, the mandato-ry wearing of masks, and social distancing are critical steps for controlling the risk of COVID-19 spread. This study was conducted to find out how these changes in daily lives impacted the distribution of respiratory microor-ganisms. Methods: A retrospective study was conducted to identify the incidence and distribution patterns of ARI-causing respiratory microorganisms before (Period I) and during the COVID-19 pandemic (Period II) in terms of detec-tion method, age, month, and season. In particular, data in Periods I and II were compared for eight major kinds of respiratory microorganisms: adenovirus (AdV), human metapneumovirus (HMPV), human rhinovirus/entero-virus (Rhino/Entero), influenza virus (Flu) A, Flu B, human parainfluenza virus (HPIV) 3, respiratory syncytial virus, and Mycoplasma pneumoniae. Results: A total of 27,191 respiratory specimens were tested, of which 5,513 were obtained from children and ado-lescents (age groups 1 ∼ 5) and 21,678 from adults (age group 6). The overall positive rates for at least one respira-tory microorganism in Periods I and II were 23.1% (1,199/5,193) and 4.9% (1,070/21,998), respectively (p < 0.001). The overall positive rates in male and female patients were significantly different (8.7% vs. 7.9%; p = 0.016). On the FilmArray. RP assay, positive rates in all age groups decreased significantly in Period II compared with Period I. AdV, Rhino/Entero, and Flu A were detected in all four seasons, but HMPV and HPIV3 were not detected. The overall positive rates on FilmArray and the Flu antigen test in Period II were significantly decreased. In the COVID-19 test, the positive rates were high in March and April 2020, and decreased thereafter, but these in-creased again in the winter of 2020/2021. Conclusions: Life changes due to COVID-19 pandemic have had a significant impact on the distribution of respi-ratory microorganisms; our study results might provide useful information on respiratory virus epidemiology.