What’s Behind the Rise in Pediatric Cases of Walking Pneumonia

Since the spring, cases of the bacterial respiratory infection commonly referred to as “walking pneumonia” have been increasing in North America, particularly among young children.

While infections from Mycoplasma pneumoniae are nothing new—the CDC estimates there are about 2 million cases annually in the U.S.—this is the first time cases have risen since the start of the COVID pandemic, and its higher prevalence in children younger than school age is uncommon.

In this Q&A, adapted from the December 9 episode of Public Health On Call, Anna Sick-Samuels, MD, MPH ’12, an assistant professor in Epidemiology and Health Policy and Management and a pediatric infectious disease doctor at Johns Hopkins Medicine, talks with Lindsay Smith Rogers all about walking pneumonia: What it is, how it’s tested for, how it can be treated and prevented, and what parents should know. 

What is walking pneumonia?

Walking pneumonia is a respiratory tract infection caused by the bacteriumMycoplasma pneumoniae.

In many cases, the person will not even know they were infected, because their body clears the infection and it never causes significant or noticeable illness. Some people may experience very mild symptoms that eventually go away without treatment; others will experience more severe symptoms that can include fever, persistent or worsening cough, sore throat, tiredness, and headache. If a person is having trouble breathing, they should be evaluated by a doctor.

Walking pneumonia doesn't tend to cause much nasal or sinus congestion in adults, who tend to experience chest cold symptoms from an infection. If someone other than a young child has a runny nose, nasal congestion, or sinus buildup, it’s more likely they have a viral infection—like the common cold, flu, or COVID—and not pneumonia.

[According to the CDC, children under 5 may experience symptoms other than a chest cold, including nasal congestion, sneezing, and watery eyes, or gastrointestinal symptoms like diarrhea and vomiting.]

How do you test for walking pneumonia?

One is a nose or throat swab, similar to a COVID test, looks for genetic pieces of the M. pneumoniae bacteria.

Some facilities may offer a respiratory pathogens panel, in which one swab is tested for a bunch of different viruses and bacteria at the same time. M. pneumoniae is often included in those panel tests. Some facilities may even have access to quick results of that panel test, which can help the practitioner decide whether antibiotics is the right treatment.

Other places might need to send the test out and wait several days for results. In that case, a doctor may not order a test and instead determine a treatment plan by evaluating the person’s symptoms, their age, whether they live or work in crowded settings, and any recent contact with other people who have been sick. A doctor may also order a chest X-ray to see if the person has pneumonia.

Is there a treatment for walking pneumonia?

Yes. M. pneumoniae can be treated with antibiotics. One of the most common is azithromycin.

How does walking pneumonia spread?

Similar to respiratory viruses like the common cold or COVID, M. pneumoniae is spread through droplets, so through our breath, coughing, and sneezing. It has to get into the airway to cause infection.

But compared to those viruses, M. pneumoniae has a much longer incubation period—the time between when you get infected and when you experience symptoms. With walking pneumonia, it can take up to three to four weeks from the time someone was exposed to the germ to the time that they're feeling sick. This makes it even harder to determine when or where someone was infected.

When is a person contagious?

Typically, a person is most contagious right when they're first experiencing symptoms, even if those symptoms are mild. A person with a fever who is coughing a lot would be spreading a lot of infectious droplets that people around them could inhale.

[According to the CDC, M. pneumoniae bacteria can persist in the respiratory tract for several months, even if no noticeable symptoms are present. These bacteria can continue to be spread through droplets, especially through the lingering cough many people experience.]

Who is most vulnerable to walking pneumonia?

The highest rates of walking pneumonia generally occur in school-age children and teens. Adults can get walking pneumonia too, but it is mostly a pediatric illness. People who have weakened immune systems or are recovering from another respiratory infection are at higher risk of severe infection from M. pneumoniae.

What’s different this season, however, is we’re also seeing younger children—two-, three-, and four-year-olds—being diagnosed with pneumonia and testing positive for M. pneumoniae.

Why is there an increase in cases now? How do current case rates compare to a normal season pre-COVID?

Before 2020, there tended to be waves of walking pneumonia every few years—there would be more cases in a particular year, and then it would subside again. And during COVID, it just went away completely because the infection prevention measures that went into place, like social distancing and masking, interrupted the spread of M. pneumoniae’s from one person to the next.

Parts of Europe and Asia reported increases in M. pneumoniae in 2023. In North America, we began to detect M. pneumoniae more frequently on tests in 2024. Since the summer, the proportion of tests that are positive for M. pneumoniae has gone up and is still going up right now.

As we head into the typical winter respiratory virus season, are you concerned about the current rates of walking pneumonia?

This is the time of the year when we see lots of respiratory infections; most of them are viral, but we expect to see some increase in bacterial pneumonia too. This year and in past years, M. pneumoniae has seen an uptick of cases in the late summer and early fall, and then it eventually starts to come down. There is plenty of M. pneumoniae getting shared around our communities right now, but not everyone who is exposed will get sick. The spread will eventually peter out and the wave of cases will die down, but we can’t exactly predict when that will be.

What signs indicate when a child needs to see a doctor?

The biggest thing to look out for is difficulty breathing. Signs that a child is working hard to breathe include flaring their nostrils when they inhale to try to open their airways, or tugging at the skin on the front of their throat when taking a deep breath. They may also be breathing fast.

Babies and toddlers who are working harder to breathe will be lethargic and have difficulty sleeping and keeping fluids down.

Those are reasons to be worried and seek care and evaluation by a health care professional.

Does walking pneumonia ever require hospitalization?

Most people do not need to be hospitalized. For many people, symptoms will go away without treatment, and some may benefit from antibiotics. A small proportion of people may need hospitalization, particularly if they’re having trouble breathing and need supplemental oxygen, or if a sick baby can’t keep hydrated and needs IV fluids.

What should parents know about preventing walking pneumonia?

M. pneumoniae infection can be prevented by the same methods we use to prevent other respiratory infections. If a child has symptoms, parents should avoid sending them to school, particularly until they are fever-free (without the use of fever-reducing medication). If a child is coughing so much that they can’t sleep well at night or participate in activities, keeping them home from school will reduce the chance of spreading any respiratory infection to others. If children are able and willing to wear a mask, that can prevent spreading some of those droplets to their friends.

Other ways to prevent spreading respiratory illnesses, including walking pneumonia, include:

• Wearing a mask around someone who is or recently was sick.
• Gathering with friends and family outside or in places with good ventilation and air filtration.
• Covering coughs and sneezes.
• Washing hands regularly, before we touch our face, eat, or interact with others.
• Be mindful at gatherings, especially if anyone in attendance is at risk for more severe illness.

Is there a vaccine for walking pneumonia?

No, M. pneumoniae infection is not vaccine-preventable. The measures mentioned above are what can help prevent spread.

There are vaccines for other viruses that circulate this time of year, including flu and COVID, as well as tools for preventing RSV. I encourage getting vaccinated against those viruses, because they’ve been shown to reduce the severity of illness and reduce the chance that we spread it between each other. For our youngest patients, these immunizations can make a dramatic difference in their outcomes if they do get infected.

This article was edited for length and clarity by Aliza Rosen.

Related:

• Is the Hygiene Hypothesis True?
• How to Protect Yourself and Others From RSV