Mycoplasma Pneumoniae Reemerges after the Pandemic

Lilian White, MD
Posted on November 18, 2024

Mycoplasma pneumoniae is a common respiratory pathogen with rising incidence over the past year. Mycoplasma pneumoniae is a cause of upper respiratory infections. In approximately 5% to 10% of cases, the infection may progress to pneumonia with the patient otherwise feeling well enough to go about their daily activities. This phenomenon resulted in the moniker walking pneumonia as early as 1888. Epidemics of M. pneumoniae tend to occur every few years.

Before the COVID-19 pandemic, M. pneumoniae was estimated to be responsible for approximately 2 million infections per year in the United States (~8% of tests in 2017–2020). Infections of M. pneumoniae are often undiagnosed, so the number of infections reported each year is an underestimate. Mycoplasma pneumoniae, similar to most respiratory pathogens, had a reduced incidence during the COVID-19 pandemic; however, although many respiratory pathogens made a comeback in 2021, M. pneumoniae remained at a low incidence until mid-2023 when it began to reemerge in various parts of the world. Some theorize this delayed re-emergence is due to the atypical characteristics and long incubation period of the bacterium.

Although pneumonia is the most common reason for hospitalization in children, it is usually caused by viruses. Mycoplasma pneumoniae tends to infect older children and young adults in the summer to early fall. This recent epidemic has been notable for a rise in incidence in children 2 to 4 years of age in addition to the usual school-aged children. Chlamydia pneumoniae is considered the most common cause of atypical pneumonia in infants. Infection with M. pneumoniae appeared to reach a peak in late August in the United States. At that time, 2% of emergency room visits were associated with M. pneumoniae across all age groups, up from 0.5% in March.

Mycoplasma pneumoniae has an incubation period of 1 to 4 weeks. Infection presents in patients with gradual onset of upper respiratory infection symptoms (e.g., cough, malaise, fever, sore throat) over 3 to 5 days. Atypical pneumonia may be suspected in cases of wheezing on exam and, if a chest x-ray is obtained, bilateral perihilar infiltrates. Diagnosis of atypical pneumonia is primarily clinical. Chest x-ray may be indicated in children with hypoxemia, lack of improvement over 48 to 72 hours, or in those with respiratory distress.

Testing for M. pneumoniae is often limited to emergency department and hospital settings due to availability. Nucleic acid amplification tests are the most sensitive and specific testing method (usually as part of a respiratory pathogen panel) and are generally the preferred method of testing; however, no test to date is 100% sensitive or specific.

Macrolides are currently recommended in the United States as the first-line antibiotic for atypical pneumonia caused by M. pneumoniae. Resistance to macrolides has been increasing worldwide, particularly in the Western Pacific region, and is highest in China at approximately 80%. Fluoroquinolone or tetracycline antibiotics may be considered as alternative options. A knowledge of local macrolide-resistance patterns may be helpful in considering treatment options. Additional information on treating community-acquired pneumonia in children is available in a previously published AFP article.

The Centers for Disease Control and Prevention hosts a Respiratory Data Illness Channel that is updated weekly with the incidence of respiratory illnesses and specifically rates of COVID-19, influenza, and RSV. Results may be available by state and, in some cases, specific counties. As of the first week of November, COVID-19 activity is overall stable or declining, with an increase in RSV infections in some regions.