Evolving clinical features of Mycoplasma pneumoniae infections following COVID-19 pandemic restrictions: a retrospective, comparative cohort study

Abstract

Since its delayed re-emergence after non-pharmaceutical interventions (NPIs) against the COVID-19 pandemic, Mycoplasma pneumoniae has caused community-acquired pneumonia outbreaks worldwide. In this study, we aimed to investigate how the clinical characteristics and severity of M. pneumoniae infections have changed after COVID-19 pandemic restriction, in order to enable adequate interpretation of clinical features and response to future M. pneumoniae epidemics. This retrospective, comparative cohort study compared clinical features and severity of children with M. pneumoniae detection by PCR during the periods April 1, 2015, to March 31, 2020 (pre-NPI); April 1, 2020, to March 31, 2022 (NPI); and April 1, 2022, to March 31, 2025 (post-NPI). Clinical features were compared between periods by Kruskal-Wallis rank sum test or Fisher's exact test, as appropriate. Moreover, we compared hospitalization and intensive care unit (ICU) admission using generalized linear models. In total, 321 patients were included in the study. Since the first detection of M. pneumoniae after the COVID-19 pandemic in summer 2023, the re-emergence has shown a bimodal curve with two distinct peaks (post-NPI first-year and second-year). The median age of patients was higher in the post-NPI than the pre-NPI period (9.05 vs 8.20 years), particularly during the first-year peak (11.00 years). Obstructive diseases were observed more frequently post-NPI compared to pre-NPI (18.6% vs 9.6%). Moreover, more patients presented with chest pain (8.9% vs 2.4%) and pleural effusions (45.7% vs 28.9%) post-NPI than pre-NPI. Conversely, extrapulmonary manifestations were less frequent post-NPI (18.6% vs 30.1%), particularly dermatological (15.7% vs 25.3%) and neurological (1.3% vs 4.8%) manifestations. Hospitalization rate (38.6% post-NPI vs 43.9% pre-NPI) and length of stay (median, 4 [IQR, 2-5] vs 4 [IQR, 3-6] days) were similar, while generalized linear models showed a trend toward fewer hospitalizations post-NPI (odds ratio [OR], 0.72 [95% CI, 0.42-1.23]; P = 0.22). The same applied to ICU admission rate (5.1% post-NPI vs 4.9% pre-NPI), with a trend toward fewer ICU admissions post-NPI (OR, 0.90 [95% CI, 0.29-3.34]; P = 0.86).

Conclusion: We observed notable changes in the clinical presentation of re-emerging M. pneumoniae infections compared to the pre-COVID-19 pandemic period, particularly an increase in obstructive phenotypes and pleural effusions. However, overall disease severity appeared to remain largely unchanged.

What is known: • The delayed re-emergence of M. pneumoniae in late 2023 was substantial in terms of case numbers across many geographical locations. • No statistically increased proportion of severe or worse outcomes of re-emerging M. pneumoniae infections could be observed globally compared with pre-COVID-19 pandemic epidemics.

What is new: • Clinical features of M. pneumoniae infections in children partly changed following COVID-19 pandemic restrictions, with new signs like obstructive phenotypes and pleural effusions. • The findings suggest that there has been no overall increase in disease severity; in fact, extrapulmonary manifestations were fewer, with trends toward reduced hospitalizations and ICU admissions.

Keywords: Community-acquired pneumonia; Epidemiology; Extrapulmonary manifestations; Non-pharmaceutical interventions (NPIs); Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

Fig. 1

Mycoplasma pneumoniae detections by PCR from April 1, 2015, to March 31, 2025, at the University Children’s Hospital Zurich, Switzerland. Detection numbers may differ from publications of the ESGMAC MAPS study [1, 5] as the detailed description of clinical characteristics in this study was subject to general consent. Abbreviations: NPI non-pharmaceutical intervention, PCR polymerase chain reaction