Changes in the Distribution of Respiratory Pathogens After the COVID-19 Pandemic.

Abstract

Background: Diverse quarantine measures against the coronavirus disease 2019 (COVID-19) pandemic have affected the distribution patterns of respiratory pathogens. This study analyzed changes in the incidence and distribution of major respiratory pathogens during the COVID-19 pandemic and after the endemic declaration. In addition, the study aimed to provide a basis for future community-centered infectious disease response strategies by identifying co-infection patterns and whether pathogens re-emerge after mitigation.

Methods: In this retrospective study, the results of 105,619 respiratory pathogen tests, including FilmArray® Respiratory Panel (BioFire Diagnostics) assay (FilmArray RP), influenza tests, and COVID-19 tests, were collected at a Korean university hospital during the COVID-19 pandemic (Period I: March 2021 through April 2023) and endemic (Period II: May 2023 through February 2025). The changes in the distribution of major pathogens, age and gender characteristics, seasonality, and co-infection patterns were compared between the two periods.

Results: The overall positivity rate for the FilmArray RP significantly increased from 64.4% in Period I to 71.1% in Period II (p < 0.001). In the age-specific analysis, age group 3 (4 months to 2 years) had the highest positivity rate in Period II (82.7%). Human rhinovirus/enterovirus was the most frequently detected pathogen, whereas respiratory syncytial virus cases increased in number, but decreased in proportion to all positive cases in Period II. The prevalence of adenoviruses and Mycoplasma pneumoniae has significantly increased since the pandemic. Human metapneumovirus has shifted its seasonality from autumn to summer and spring, whereas parainfluenza virus 3 has shifted from autumn to spring and summer. Among all positive cases, co-infections significantly increased to 17.6% and 22.3% during Periods I and II, respectively (p < 0.001).

Conclusions: This study revealed significant changes in the incidence, seasonality, age characteristics, and co-infection patterns of respiratory pathogens after the mitigation of COVID-19. These changes result from the re-emergence of pathogens that were suppressed during the pandemic, immune vaccination, and the resumption of social activities, suggesting the need to establish an age- and pathogen-specific surveillance system for future infec-tious disease responses.