Variability in Mycoplasma pneumoniae testing practices highlights the need for diagnostic best practices in children hospitalized with respiratory illnesses, as well as the need for a national surveillance system for the infection, new research showed.

The study found a fivefold increase and striking institutional variability in M pneumoniae testing in children hospitalized for respiratory illnesses. The researchers, from Stanford University in California, conducted the research after noting a surge in the number of children admitted to their hospital with M pneumoniae infections.

“While there are normally cycles of this infection every 3-5 years in the general population, it is usually a relatively small proportion of the hospitalizations for respiratory illnesses in children,” said Hannah Bassett, MD, a clinical associate professor in the Division of Pediatric Hospital Medicine at Stanford, who led the study. “However, at our institution, we noted unprecedented levels of children admitted with respiratory illnesses caused by Mycoplasma in 2024-2026. Clinically, we noted delays in testing and treatment that may have impacted outcomes.”

M pneumoniae cannot be treated by the same antibiotics that are used to treat typical community-acquired pneumonia, added Bassett, who presented the findings at Pediatric Hospital Medicine (PHM) 2026. “Therefore, high suspicion for the infection and early testing is important to ensure children receive appropriate antibiotics.”

To conduct their study, Bassett and her colleagues used Cosmos from Epic, the electronic health records company. They identified hospital admissions between 2016 and 2025 of children (age, < 18 years) with a diagnosis of community-acquired pneumonia, asthma, or bronchiolitis. They looked at the proportion of these admissions with a M pneumoniae test, a diagnosis code for M pneumoniae, and/or receipt of antibiotic therapy for the infection. They also looked at the variability of M pneumoniae testing during these admissions across the institutions that contribute data to Cosmos.

Among 982,017 patients from 255 hospitals in the analysis, the researchers observed a fivefold increase in M pneumoniae diagnoses in 2024. However, testing for the infection increased consistently over the past decade, including prior to the most recent spike in cases. Testing during hospital admissions for pediatric respiratory illnesses has increased from approximately 7% of encounters in 2016 to almost 34% of encounters in 2025.

But testing across institutions varied. For example, in 2025 the researchers found rates of testing ranged from less than 10% of relevant hospitalizations to more than half in some institutions.

Bassett said recent reports have noted increases in M pneumoniae in the US. “The recent epidemic of M pneumoniae in the US highlights the need to better understand the relationship between [M pneumoniae] testing, treatment, and outcomes in children hospitalized with respiratory illnesses,” Bassett said. “Variability in testing practices could impact clinical outcomes for children hospitalized with respiratory illnesses, especially during peak [M pneumoniae] years as delays in testing and diagnosis could lead to delays in appropriate antibiotic administration and therefore potentially more prolonged or severe illness.”

Danielle M. Zerr, MD, a professor of pediatrics at the University of Washington School of Medicine and at Seattle Children’s Hospital, both in Seattle, who was not involved with the study, said the report “provides additional data supporting a recent increase in M pneumoniae activity.”

“During the [COVID] pandemic, we saw levels of M pneumoniae drop. As described by the CDC in 2024, we saw levels increase, including in young children,” Zerr said. “Typically, M pneumoniae is more commonly diagnosed in older children and adolescents.”

Bassett and Zerr reported having no relevant disclosures.

Kate O’Rourke is a freelance journalist in Portland, Maine.