Key Points

An unusually severe outbreak of Mycoplasma pneumoniae infections has been observed in France among children and young adults since November 2023. Epidemiological indicators rose sharply in urban areas and hospitals, peaking in early January 2024. A decline was then observed for most indicators, followed by stabilization since early February 2024 at levels that remain, however, higher than those of the years preceding the COVID-19 pandemic. In this context, monitoring of the situation continues through a system coordinated by Santé publique France in conjunction with several networks and data sources in community settings and hospitals.

• Following the sharp increase in the use of emergency care for pneumonia of all causes in the community (SOS Médecins network) and in emergency departments (Oscour® network), and for bacterial pneumonia in emergency departments between late October 2023 (S43/23) and December 2023 (S52/23), a decrease in January 2024 (S01-S04/24) followed by stabilization among 5- to 14-year-olds and a downward trend among 15- to 44-year-olds in February (S05-S09/24), at levels remaining higher than those observed in previous years.

• In hospitals, following a sharp increase in the PCR detection rate for M. pneumoniae from October (W40/23) to mid-January (W03/24), there was a decrease in late January (W04) followed by stabilization in February (W05–W08), which continued into March (W09–W12/24).

• In the community, a sharp increase in the positivity rate of IgM tests for M. pneumoniae from late October (S43/23) to late January (S05/24) among those aged 5–44, followed by a temporary decrease in mid-February (S07–S08/24) and then an increase in late February (S09). A trend toward stabilization began between early and late March (W10–W12/24).

• A low proportion (2.4%) of strains resistant to macrolides (first-line antibiotic treatment) among samples analyzed between weeks 27/2023 and 11/2024.

• As of March 24, 2024, indicators showed a trend toward stabilization or decline, though levels remained higher than those in the years preceding the COVID-19 pandemic.