Resurgence of Macrolide-Resistant Mycoplasma pneumoniae After the COVID-19 Pandemic at a Children's Hospital in Japan.

BACKGROUND: Mycoplasma pneumoniae is a leading cause of pediatric community-acquired pneumonia. Macrolide-resistant M. pneumoniae (MRMP) emerged in East Asia in the 2000s and was once highly prevalent in Japan. However, its epidemiology in Japan following the coronavirus disease 2019 (COVID-19) pandemic is unclear. METHODS: The present, single-center, retrospective study, conducted at a tertiary children's hospital in Tokyo, investigated the post-pandemic prevalence of MRMP and compared the clinical features of MRMP and macrolide-susceptible M. pneumoniae (MSMP). Patients aged ≤ 18 years who were positive for M. pneumoniae on polymerase chain reaction (PCR) between April 2020 and March 2025 were enrolled. MRMP was defined by macrolide-resistance mutations detected using a point-of-care, PCR-based assay. The proportion of patients with MRMP and the clinical characteristics of the MRMP and MSMP cohorts were analyzed. RESULTS: In total, 272 patients had a M. pneumoniae infection, and 191 (70.2%) patients were classified into the MRMP group. A marked resurgence of M. pneumoniae infections, of which MRMP comprised 87% of the cases, was observed in April 2024 and peaked in October 2024. Among hospitalized patient (52/272, 19.1%), MRMP group were more likely to require oxygen (89% vs. 43%, p = 0.0015), and experience respiratory complications (47% vs. 7.1%, p = 0.019) than MSMP group. CONCLUSION: MRMP reemerged as the predominant strain in Tokyo following the COVID-19 pandemic and may be associated with greater severity and recalcitrance to treatment. Therefore, monitoring its prevalence and adjusting the antibiotic strategy are crucial.