Mycoplasma pneumoniae incidence, phenotype, and severity in children and adolescents in Denmark before, during, and after the COVID-19 pandemic: a nationwide multicentre population-based cohort study

Abstract

Mycoplasma pneumoniae infections resurged globally in 2023-2024 after a three-year decline during the COVID-19 pandemic. We explored the incidence and severity of M pneumoniae infections in children and adolescents before, during, and after the pandemic. This nationwide, population-based cohort study included all Danish children and adolescents aged 0-17 years with a positive M pneumoniae PCR test from May 1, 2016, to April 30, 2024. We obtained clinical details for patients hospitalised for 24h or more. Risk ratios for infections, hospitalisations, and disease manifestations in 2023-2024 versus pre-COVID-19 seasons were calculated using Fisher's exact and Pearson's χ2 tests. A season was defined from May 1 to April30. Among the Danish population of 1,152,000 children and adolescents, 14,241 with a positive PCR test for Mpneumoniae were included. In 2023-2024, children and adolescents with a positive PCR rose 2.9-fold (95% CI 2.8-3.1; p<0.0001) compared to the pre-COVID-19 seasons, and hospitalisations rose 2.6-fold (95% CI 2.0-3.3; p<0.0001). Mpneumoniae-induced rash and mucositis increased 5.3-fold (95% CI 1.8-15.3; p=0.0007). In 2023-2024 compared to the pre-COVID-19 seasons, there was no difference in the proportion of hospitalisation (360 [4%] of 8165 versus 230 [4%] of 6009; p=0.09), the median duration of hospital stay (3 days [IQR 2-5] versus 3 days [IQR2-5]; p=0.84), or paediatric intensive care unit admission (14 [4%] of 360 versus 9 [4%] of 230 p=1.00). In Denmark, M pneumoniae infections and hospitalisations increased three-fold in 2023-2024 compared with the pre-COVID-19 seasons, indicating an immunity debt caused by the decline in M pneumoniae during the COVID-19 pandemic. While the severity of M pneumoniae infections did not change in 2023-2024, the five-fold increase in M pneumoniae-induced rash and mucositis in children and adolescents highlights Mpneumoniae as an important pathogen causing mucocutaneous eruptions. Innovation Fund Denmark and Rigshospitalets Forskningsfond.