Walking pneumonia is spreading. Doctors share the tell-tale symptoms to look for, and varied ways to treat it.

• Walking pneumonia infections rose nationwide as kids returned to school this fall.
• The infection can be tricky to diagnose, and testing is expensive.
• Doctors may choose different antibiotics to try first, working on a case-by-case basis.

A common infection known as "walking pneumonia" has been on an uptick across the US in recent months, especially among kids and teens.

The respiratory illness caused by mycoplasma pneumoniae bacteria is often called walking pneumonia because it tends to be milder than other lung infections. Patients may feel run down, with a cough and a slight fever, but are often still well enough to continue their daily life.

"It can be a little incognito, it can sneak up on people," Dr. Elizabeth Schlaudecker, medical director of infectious diseases at Cincinnati Children's Hospital, told Business Insider.

The illness can be tough to identify and expensive to test for, and it can linger for several weeks, making it a frustrating sickness for families. Plus, treatment isn't necessarily one-size-fits-all.

Here's what to know about how to spot it and treat it.

Look out for a persistent cough, fever, and fatigue

The tell-tale signs of walking pneumonia are not obvious. Illnesses caused by mycoplasma pneumoniae tend to be milder than infections caused by the more common bacterial pneumonia, streptococcus pneumoniae.

ER doctor Russell Migita at Seattle Children's Hospital says it's hard to know exactly how many of the patients he sees have walking pneumonia cases, versus strep pneumonia or viral pneumonia. Often, doctors use a stethoscope to listen for a characteristic, localized "crackling" noise in patients with walking pneumonia, but not every patient has that.

Testing for the bacteria that causes walking pneumonia is also expensive, relatively new, imperfect, and may not be covered by insurance, Migita said, so it's hard for experts to know exactly how bad this fall outbreak really is, compared to years past.

The latest CDC data on the tests that are being done suggests more toddlers are getting walking pneumonia this year than was thought to be typical; the illness used to be viewed as more common in school-age kids. There have also been outbreaks among young adults living in dorms, where the bacteria has plenty of time to incubate and spread.

Schlaudecker is part of the CDC surveillance network testing patients for mycoplasma bacteria across the country. She said test results indicate a surge in infections peaked in late August and early September as kids headed back to school, and started trading germs again. "Hopefully it's starting to slowly decline, but we're definitely still seeing it," she said.

People who've recently had the flu are also at increased risk for developing walking pneumonia.

Amoxicillin may not be your doctor's first choice

New studies suggest there isn't always a clear winner when it comes to the best treatment for walking pneumonia.

Even though macrolide antibiotics, like azithromycin, are the recommended treatment and should perform better than penicillin-based antibiotics like amoxicillin on this bacteria, there isn't great data on which medication actually helps shorten and improve the course of this infectious disease best.

In practice, Migita says doctors often use a mix of their own experience, local disease trends, and a particular patient's history and preferences to get a sense of what might work. In some cases, patients will get better without medication, but for bacterial pneumonia, an antibiotic can help. Doctors assess the situation on a case-by-case basis, similar to how they would treat an ear infection.

"Empiric treatment is what we do in most cases for most pediatric infections because it's hard to say for sure what's causing it," he said. "If you're not getting better on your first antibiotic in two to three days, then get seen again."

Doctors say even though walking pneumonia doesn't tend to be as severe as other seasonal illnesses kids pass around like the flu, COVID, or RSV, it can still be a burdensome one for families, because it tends to last for a long time. In rare cases, walking pneumonia can prompt brain swelling, kidney issues, and difficulty breathing, and people with lung issues, and weakened immune systems may be especially at risk of hospitalization with walking pneumonia.

Earlier this year, Schlaudecker's 15-year-old daughter had a persistent cough that continued for a week after what her mom thought was just a cold. They went to see her pediatrician, who listened to the girl's chest with a stethoscope.

Without any testing, the daughter was diagnosed with walking pneumonia, and prescribed a Z-Pak (azithromycin). Within 24 hours of beginning her medication, the teenager felt great again.

"She was like, 'Wow, this is so cool that we figured out what it was and got on the right drug," Schlaudecker said. "It was a good medical success story."