Lessons From 2024 Spike in M. pneumoniae–Associated Pneumonia
Research By: Samir S. Shah, MD, MSCE, MHM
Post Date: June 26, 2025 | Publish Date: June 26, 2025
Last year, hospitals across the U.S. witnessed an unusual spike in children requiring hospitalization to treat pneumonia caused by the bacterium Mycoplasma pneumoniae (M. pneumoniae).
Typically, this pathogen surges as a cause of pneumonia every three to five years as population immunity from previous infections wanes. However, the 2024 increase was unusually large, which prompted experts from the Centers for Disease Control and Prevention, Cincinnati Children’s, the University of Utah and the Children’s Hospital Association to investigate. Their findings were published June 26, 2025, in the CDC’s Morbidity and Mortality Weekly Report.
M. pneumoniae treatment differs from other causes
In most cases, M. pneumoniae infections are relatively mild and do not require hospital care. The pathogen is one of the leading causes of so-called “walking pneumonia.” However, some infected people do get very sick.
When serious cases occur, understanding which pathogen is involved is important. The M. pneumoniae bacterium lacks a cell wall, which makes it naturally resistant to beta-lactam antibiotics such as amoxicillin. Instead, clinicians treat M. pneumoniae with macrolides, tetracyclines, or fluoroquinolones.
An unusual year
In 2024, researchers found that 10,298 children were hospitalized with M. pneumoniae infections at one of the 42 children’s hospitals that report data to the Children’s Hospital Association, a sharp increase from a total of 6,055 (combined) that occurred during 2018–2023.
At its peak, in July 2024, this pathogen accounted for 53.8% of all the pneumonia cases in the pediatric hospitals. In a typical year, less than 5% of hospitalizations are caused by M. pneumoniae.
Another odd trend: the infections rose the fastest among 1-year-olds compared to other ages. In past years, hospitalized children have generally been aged 5 and older.
“We think the surge reflects an increased population-wide susceptibility following the COVID-19 pandemic,” says study co-author Samir Shah, MD, MSCE, MHM, vice chair for clinical affairs and education at Cincinnati Children’s. “During the COVID years, we saw very low levels of M. pneumoniae circulating worldwide. So, when the 2024 cyclical increase occurred, there was a much larger pool of at-risk children.”
While the number of cases surged, the researchers found that the severity of the illnesses did not change. In fact, the average lengths of the hospital stays that occurred in 2024 were slightly less than the hospital stays in 2018-2023.
Looking forward
The co-authors recommend that hospitals be vigilant about the cyclical nature of M. pneumoniae, so that they can be prepared to adjust their diagnostic approach and, if necessary, empiric antibiotic therapy.
This pathogen can trigger pneumonia at any time of year, not just in winter. Additionally, M. pneumoniae infection cannot be identified solely based on physical examination, so providers should consider laboratory testing to guide their treatment plans.
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| Original title: | Mycoplasma pneumoniae Infections in Hospitalized Children — United States, 2018–2024 |
| Published in: | MMWR |
| Publish date: | June 26, 2025 |
Research By
I’m a board certified pediatric hospital medicine and pediatric infectious disease physician. My research focuses on improving the efficiency and quality of care of children — particularly those hospitalized with common, serious infections such as pneumonia and meningitis.
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The Research Horizons blog features news and insights about the latest discoveries and innovations developed by the scientists of Cincinnati Children's. This blog does not provide medical advice, diagnosis, or treatment.
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