Post-pandemic surge of Mycoplasma pneumoniae in Ontario, 2024: molecular surveillance and resistance trends relative to 2018–2023

ABSTRACT Mycoplasma pneumoniae (Mpn) is a common respiratory tract pathogen known to cause cyclic epidemics every 3–4 years. For 4 years (2020–2023), a low positivity rate (0.64%) for Mpn laboratory testing at Public Health Ontario suggested minimal circulation of Mpn in Ontario, Canada, likely owing, in part, to COVID-19-related non-pharmaceutical interventions. In 2024, we observed a dramatic re-emergence of Mpn, characterized by large increases in the number of laboratory-confirmed cases ( n = 1,122) and the positivity rate (19.1%) of laboratory detections. Patient age distribution of Mpn infections in 2024 did not differ from 2018 to 2019; however, analysis of patient setting at the time of specimen collection as a proxy for disease severity saw a significant increase in the proportion of Mpn-positive specimens collected from patients in hospital emergency departments (ED) ( P < 0.001), and a decrease in the proportion from patients in inpatient wards ( P = 0.001). Macrolide-resistant rates were statistically equivalent in 2024 (14.6%) compared to 2018–2019 (12.4%), as was the ratio of p1 -1 and p1 -2 adhesin subtypes. Combined 2018–2024 data show that a significantly greater proportion of Mpn-positive pediatric specimens occurred in community clinics/private practices ( P = 0.001), compared with adults, where a greater proportion were in EDs ( P = 0.012), or intensive/critical care units ( P < 0.001). Our findings suggest that the magnitude of Mpn infections in 2024 was not due to a novel strain, but rather due to the increased transmission of strains previously circulating in Ontario following the cessation of COVID-19 pandemic-related non-pharmaceutical interventions, and exacerbated by population immunity debt and the cyclic nature of Mpn. IMPORTANCE Mycoplasma pneumoniae (Mpn) is a common cause of community-acquired respiratory infection and is known for causing “atypical” pneumonia. Infections show seasonal and cyclical patterns with larger epidemics every 3–4 years. Because Mpn is transmitted via respiratory droplets, incidence was very low during the COVID-19 pandemic when masking and physical distancing were widely utilized. In late 2023 through 2024, many jurisdictions worldwide reported a surge in Mpn cases. This increase, along with reports of emerging resistance to first-line treatment macrolide antibiotics, raised concerns about the management of severe infections. Here, we describe the post-COVID-19 pandemic re-emergence in Mpn in Ontario, Canada. Despite high case numbers detected in 2024, infections were not more severe than in pre-pandemic years (2018–2019). Mpn genotype ratios and macrolide resistance rates were statistically comparable between 2018/2019 and 2024, suggesting re-emergence of previously circulating strains rather than the introduction of a novel hypervirulent strain.