France has experienced an unusually intense outbreak of Mycoplasma pneumoniae pneumonia since October 2023, with a significant rise in cases since early November.

Is it a cause for concern?

M. pneumoniae is an atypical bacterium and ranks second only to Streptococcus pneumoniae in causing acute bacterial pneumonia, especially in children and young adults. While the majority of infections caused by this bacterium, such as rhinopharyngitis, tracheobronchitis, and acute bronchitis, are generally benign and resolve on their own, there can be complications, including exacerbation of asthma or rare manifestations, such as cutaneous or neurological issues, which may require hospitalisation.

When Should It Be Considered?

Consider M. pneumoniae infection in the following scenarios:

• Pneumonia, especially when accompanied by muscle pain.
• Signs suggestive of an atypical bacterium: gradual onset, extrarespiratory signs, preserved general condition, and not well systematised opacity in chest X-rays.
• Dermatological lesions.
• Hepatic cytolysis.
• Presence of clustered cases in a community.

A chest X-ray can aid in diagnosis, showing a diffuse bilateral interstitial pulmonary infiltrate appearance. However, radiological anomalies are inconsistent, and low-dose chest CT performs better in this regard. Additional investigations depend on the severity of the pneumonia and should not delay empirical treatment initiation.

If needed, the diagnosis can be confirmed in a hospital setting through PCR testing on respiratory, pharyngeal, or nasopharyngeal samples and/or serological diagnosis. Currently, health insurance in France does not cover PCR testing in an outpatient setting.

What Is the Treatment?

M. pneumoniae lacks a cell wall, making it insensitive to beta-lactams. Therefore, macrolides are the first-line antibiotic therapy. However, in the absence of initial signs suggestive of an atypical bacterium:

• Investigate viral origins, such as influenza, COVID-19, or respiratory syncytial virus (RSV).

If the infection appears bacterial without signs pointing to M. pneumoniae, the first-line treatment remains amoxicillin or amoxicillin/clavulanic acid combination, according to usual recommendations. A clinical re-evaluation at 48-72 hours is then imperative, and a diagnosis of Mycoplasma pneumoniae must be considered in the event of failure, prompting a change of antibiotic to a macrolide after taking a control chest X-ray to rule out pleural effusion and/or a test for C-reactive protein. 

How Can It Be Prevented?

The recent resurgence follows a period of more than 3 years of very low circulation. M. pneumoniae is transmitted through respiratory droplets during close contact, and the hygiene measures put in place during the COVID-19 pandemic were effective against this bacterium. The incubation period is 1 to 3 weeks.