On October 1​​8, 2024, the U.S. Centers for Disease Control and Prevention (CDC)  released a bulletin warning of increasing number of Mycoplasma pneumoniae (M. pneumoniae) infections, particularly among young children, since late spring. There is no national reporting requirement or dedicated surveillance system to track M. pneumoniae infections, howev​er CDC use​s syndromic and commercial laboratory data to track national trends.  

CDC reported that the proportion of patients discharged from emergency departments with a diagnosis of M. pneumoniae-associated pneumonia or acute bronchitis increased since March 2024, peaking in late August but continuing to remain high as of early October. The increases were highest among children, with a notable increase in children ages 2–4 years, an age group in which M. pneumoniae has not historically been recognized as a leading cause of pneumonia.  ​

There is no California-specific reporting requirement or surveillance system for M. pneumoniae, so data on California-specific trends in M. pneumoniae infections are not available. The California Department of Public Health (CDPH) has received anecdotal reports from some local health departments (LHDs) and hospitals about increased numbers of children hospitalized with pneumonia who have tested positive for M. pneumoniae infection. ​

M. pneu​moniae Background 

M. pneumoniae is a type of bacteria that is spread from person to person through contaminated respiratory droplets. Infection usually causes mild respiratory illness but can also cause more severe disease requiring hospital care, including new or worsening asthma, severe pneumonia, and encephalitis. M. pneumoniae infections can occur at any age, but they most often occur among children ages 5–17 years and young adults. Persons recovering from respiratory illness or who have weakened immune systems are at risk for more severe disease.  

The number of M. pneumoniae infections varies seasonally and are more common in summer and early fall. Infections also follow a cyclical pattern, with the number of M. pneumoniae infections usually peaking every 3 to 7 years. During the COVID-19 pandemic the percentage of M. pneumoniae diagnoses and positive M. pneumoniae test results decreased but began to increase during the fall of 2023. 

Most people with mild M. pneumoniae infections will recover without specific treatment, but people with more severe illness may require antibiotics. M. pneumoniae bacteria are naturally resistant to certain antibiotics (e.g., beta-lactams such as amoxicillin) that are commonly used to treat other kinds of bacterial pneumonia. Therefore, the diagnosis of M. pneumoniae infection should be considered for patients with community-acquired pneumonia who are not clinically improving on antibiotics that are not effective against M. pneumoniae infection.  Macrolides (e.g., azithromycin) are the first-line antibiotic treatment for M. pneumoniae infection. Macrolide-resistance in M. pneumoniae is estimated to be less than 10% nationally but may be higher in certain regions or within clusters or outbreaks. Thus, macrolide-resistance should be considered in patients with laboratory-confirmed M. pneumoniae infection not improving on macrolides. ​

Recomm​endations 

Healthcare Pr​oviders 

• Consider the possibility of M. pneumoniae infection in children with community acquired pneumonia, especially those who are not clinically improving on antibiotics that are known to be ineffective against M. pneumoniae, such as beta-lactams. 

• If M. pneumoni​ae infection is suspected, especially among hospitalized children, perform laboratory testing to confirm the diagnosis and ensure appropriate antibiotic therapy is administered. 

• Consider swabbing both the throat and the nasopharynx to improve the likelihood of detection in respiratory swab specimens. 

• Consider using a second-line antibiotic regimen, such as fluoroquinolones or tetracyclines, depending on the patient’s age, to treat patients with suspected or confirmed M. pneumoniae infection who aren't improving on macrolides. 

• Although individual cases of M. pneumoniae infection are not reportable to public health, identified outbreaks (e.g., in an institutionalized setting such as daycare, school, etc.) should be reported to the LHD.