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. 2025 Jun;30(23):2400682.
doi: 10.2807/1560-7917.ES.2025.30.23.2400682.

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

Florian Tagini  1 , Søren Anker Uldum  2 , Carla Berengua  3 , Branislav Ivan  4 , Riccarda Capaul  5 , Sophie Edouard  6 , Adrien Fischer  7 , Jacky Flipse  8 , Diego García Martínez de Artola  9 , Daniel Goldenberger  4 , Edou Heddema  10 , Mirjam Hermans  11 , Frank Imkamp  12 , Darja Keše  13 , Clara Lejarraga  14 , Reto Lienhard  15 , Carola Maffioli  16 , Veerle Matheeussen  17 , Patrick M Meyer Sauteur  18 , Irena Mitrovic  19 , Onya Opota  1 , Christina Orasch  20 , Pavel Drevinek  21 , Olivia Peuchant  22 , Liu Po-Yu  23 , Mirja Puolakkainen  24 , Melissa Remy  20 , Khoa Td Thai  25 , Nadia Wohlwend  26 , Gilbert Greub  1 ; ESCMID Study Group for Mycoplasma and Chlamydia infections (ESGMAC)  27
Affiliations

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

Florian Tagini et al. Euro Surveill. 2025 Jun.

Abstract

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 Chlamydia pneumoniae outbreak in Switzerland, prompting the need for a better understanding of C. pneumoniae epidemiology.AimTo assess temporal and geographical variations in C. pneumoniae detection before, during and after the COVID-19 pandemic.MethodsData on C. pneumoniae 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.ResultsC. pneumoniae 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 C. pneumoniae epidemiology, with reduced detection during the pandemic and partial resurgence afterwards. Regional variations suggest differing NPI impacts and underscore the need for continued surveillance.

Keywords: PCR; asthma; bronchitis; molecular diagnosis; outbreak; pneumonia; upsurge.

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Conflict of interest statement

Conflict of interest: None declared.

Figures

Figure 1
Figure 1
Study dissemination and data collection leading to two complete datasets, encompassing sites in Europe and Taiwan, 1 November 2023–31 March 2024
Figure 2
Figure 2
Monthly variation in PCR detection ratios of Chlamydia pneumoniae, 19 European sites and Taiwan, 2018–2023
Figure 3
Figure 3
Annual PCR detection ratios for Chlamydia pneumoniae, 19 European sites and Taiwan, 2018–2023
Figure 4
Figure 4
PCR detection ratios for Chlamydia pneumoniae, 27 European sites and Taiwan, 2023
See this image and copyright information in PMC

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