Epidemiological changes in Chlamydia pneumoniae molecular detections before, during and after the COVID-19 pandemic in 27 European sites and Taiwan, 2018 to 2023

BackgroundDuring the COVID-19 pandemic, non-pharmaceutical interventions (NPIs) such as social distancing, lockdowns and enhanced hygiene led to a decrease in respiratory pathogens. However, as NPIs were relaxed, a resurgence in several respiratory pathogens was observed including one local <i>Chlamydia pneumoniae</i> outbreak in Switzerland, prompting the need for a better understanding of <i>C. pneumoniae</i> epidemiology.AimTo assess temporal and geographical variations in <i>C. pneumoniae</i> detection before, during and after the COVID-19 pandemic.MethodsData on <i>C. pneumoniae</i> PCR detection ratios (number of positive tests/ total number of tests) across pre-pandemic (2018-2019), pandemic (2020-2022) and post-pandemic (2023) periods were collected via a global survey disseminated through various professional networks.Results<i>C. pneumoniae</i> detection ratios were analysed across 28 sites (27 in Europe, one in Taiwan) in 2023 (Dataset A, n = 172,223 tests) and 20 sites from 2018 to 2023 (Dataset B, n = 693,106 tests). Twenty-seven sites were laboratories (hospital or clinical) and one a surveillance system (Denmark). A significant decrease in detection ratios was observed during the pandemic period (from 1.05% to 0.23%, p < 0.001). In 2023, detection ratios increased to 0.28% (p < 0.002). Notable regional variations were found, with statistically significant increases in detection ratios at six sites located in Switzerland and Slovenia, where ratios ranged from 0.52% to 3.25%.DiscussionThe study highlights how NPIs influenced <i>C. pneumoniae</i> epidemiology, with reduced detection during the pandemic and partial resurgence afterwards. Regional variations suggest differing NPI impacts and underscore the need for continued surveillance.