Mycoplasma pneumonia is a lung infection caused by the bacterium Mycoplasma pneumoniae, and it’s one of the most common causes of community-acquired pneumonia. It’s often called “walking pneumonia” because the symptoms tend to be milder than typical pneumonia, meaning most people stay on their feet and go about their daily lives while sick. The infection spreads through respiratory droplets during close contact and has a notably long incubation period of 1 to 4 weeks, which means you can be exposed and feel fine for days or even weeks before symptoms appear.
Why This Bacterium Is Unusual
Mycoplasma pneumoniae is technically a bacterium, but it behaves differently from the bacteria that cause most other types of pneumonia. Its defining characteristic is that it lacks a cell wall. This matters because many common antibiotics, including penicillin and related drugs (called beta-lactams), work by attacking the bacterial cell wall. Since there’s no wall to attack, those antibiotics are completely useless against mycoplasma. If you’ve been prescribed penicillin or amoxicillin and your pneumonia isn’t improving, a mycoplasma infection may be the reason.
The bacterium is also extremely small and grows slowly in laboratory cultures, which historically made it difficult to detect. It attaches to the lining of your airways and damages cells gradually rather than causing the sudden, dramatic inflammation typical of other bacterial pneumonias. This slow progression is why symptoms tend to creep in over days rather than hitting all at once.
Symptoms Compared to Typical Pneumonia
The hallmark of mycoplasma pneumonia is that it feels more like a persistent, annoying cold than a serious lung infection. The key differences from typical bacterial pneumonia:
- Fever: Walking pneumonia produces a low-grade fever, while typical pneumonia causes higher fevers ranging from 101 to 105°F (38 to 40°C).
- Cough: Mycoplasma triggers a dry, hacking cough that doesn’t produce mucus. Typical pneumonia usually causes a wet, productive cough with phlegm.
- Overall severity: Most people with mycoplasma pneumonia feel tired and run-down but can still function. Typical bacterial pneumonia more often puts people in bed or in the hospital.
Other common symptoms include headache, sore throat, and general fatigue. The cough can be the most persistent part, sometimes lingering for weeks even after you start feeling better overall. Because the symptoms are relatively mild, many people don’t realize they have pneumonia at all and assume they’re dealing with a bad cold or bronchitis.
Who Gets It Most Often
Mycoplasma pneumonia can affect anyone, but it’s especially common in school-aged children, teenagers, and young adults. Close-contact environments like schools, college dorms, and military barracks are classic settings for outbreaks because the bacterium spreads through coughing and sneezing in proximity.
The infection saw a dramatic surge in 2024. CDC data from 42 U.S. children’s hospitals showed that mycoplasma accounted for less than 5% of hospitalized pneumonia cases annually from 2021 to 2023, then jumped to 33% in 2024, peaking at nearly 54% in July 2024. The hospitalization rate among children rose from 2.1 per 1,000 hospitalizations during 2018 to 2023 to 12.5 per 1,000 in 2024 alone. A similar pattern played out worldwide, with increases appearing in other countries starting in 2023 before reaching the U.S. the following year.
The likely explanation is a “immunity gap.” Mycoplasma transmission dropped sharply during the COVID-19 pandemic when masking and distancing were widespread, then stayed low through 2023. That meant a larger pool of children who had never been exposed and had no immune defenses against it when the bacterium began circulating widely again.
How It’s Diagnosed
Because mycoplasma pneumonia looks and sounds a lot like other respiratory infections, diagnosis usually requires a lab test. Chest X-rays aren’t very helpful for distinguishing it from other causes. The patterns on imaging are nonspecific: patchy areas of lung consolidation, small nodules, or a mix of both. About 11% of patients in one study had chest X-rays that looked essentially normal aside from mild airway thickening.
The preferred diagnostic method is a molecular test (called a NAAT) that detects the bacterium’s genetic material from a throat or nasal swab. These tests are highly accurate and return results quickly enough to guide treatment decisions. Older blood-based antibody tests are still used in some settings but are less reliable. They often require two blood draws weeks apart to confirm a rising antibody level, which makes them impractical for timely treatment. Culturing the bacterium in a lab is possible but takes so long that it’s reserved for specialized research settings.
Treatment and Antibiotic Resistance
Because standard penicillin-type antibiotics don’t work, mycoplasma pneumonia is treated with different antibiotic classes. Macrolides are the first choice and can be used in both children and adults. If a patient isn’t improving on macrolides, doctors may switch to tetracyclines (for older children and adults) or fluoroquinolones (for adults only). Tetracyclines and fluoroquinolones are generally not prescribed for young children.
Many cases of mycoplasma pneumonia, especially mild ones, resolve on their own without antibiotics. But treatment can shorten the duration of symptoms and reduce the risk of spreading the infection to others.
Antibiotic resistance is an emerging concern, though the picture varies wildly by region. In the U.S., resistance rates remain relatively low. A 2024 study from Ohio found that 2.4% of mycoplasma samples carried mutations conferring macrolide resistance, with rates ticking up to 4.4% by September 2024. Southeast Germany reported a similar 2.6% resistance rate. Southern China, however, reported macrolide resistance in 96.4% of strains, a staggering difference that reflects years of heavier macrolide use in that region. For most patients in the U.S. and Europe, first-line treatment still works, but rising resistance means doctors are increasingly alert to cases that don’t respond.
Possible Complications
The vast majority of people recover fully without any lasting effects. Severe complications are uncommon but do occur, and they can extend beyond the lungs. Encephalitis, an inflammation of the brain, is one of the more serious possibilities. Skin reactions are another category of complications, ranging from relatively mild rashes to rare but severe conditions where the skin blisters and peels. Children and people with weakened immune systems are at higher risk for these uncommon outcomes.
Hospitalization rates, while still low overall, increased substantially during the 2024 surge. Among the more than 10,000 mycoplasma-related pediatric hospital discharges recorded that year, most children recovered, but the sheer volume highlighted that “walking pneumonia” isn’t always as benign as its nickname suggests, particularly when it sweeps through a population with limited prior immunity.