SEATTLE — This holiday season, try not to give your loved ones something that will take their breath away. At least, not like this.

This year, in addition to more familiar respiratory viruses like influenza, RSV and SARS-CoV-2, local health experts are also warning about a particular type of pneumonia infection.

Infections caused by Mycoplasma pneumoniae bacteria — often associated with "walking" pneumonia — have startled providers as cases have surged through the United States since the spring, especially in young children. Infections appeared to peak in late August, but have stayed at high levels, the Centers for Disease Control and Prevention warned in October.

Mycoplasma pneumonia levels remain elevated

Infections caused by Mycoplasma pneumoniae bacteria—often associated with "walking pneumonia"—have been rising in Washington and nationally. In King County, providers noticed an increase in the percentage of emergency department visits with M. pneumonia diagnosis across all ages, especially among those 5 to 17 years old.

"We've seen a dramatic increase in illness and hospitalization due to Mycoplasma pneumonia," said Dr. Mary Fairchok, a pediatric infectious diseases doctor at Mary Bridge Children's Hospital in Tacoma. "Adults can get Mycoplasma too, but it's really hitting the pediatric population."

Seattle Children's has experienced a similar wave. Earlier this year, the hospital saw between zero and four cases of Mycoplasma pneumonia in a typical week, said Dr. Danielle Zerr, chief of infectious diseases and virology at Children's. In the past couple of months, the hospital has seen between 13 and 26 cases per week.

"We're thinking this is it coming back, as we've seen other infections come back," Zerr said. "We're basically catching up to where we were prepandemic."

In King County, the percentage of emergency department patients diagnosed with Mycoplasma pneumonia has increased, especially among those under 18, according to Public Health — Seattle & King County.

While the state Department of Health doesn't specifically track cases linked to the bacteria, as Mycoplasma pneumonia isn't one of the CDC's notifiable conditions, epidemiologists have also seen an "observed increase in provider diagnoses" statewide, according to a department spokesperson.

Other viruses are also starting to pick up as we enter the heart of respiratory illness season. Here's what to know about what's circulating in the Seattle area and throughout Washington.

Pneumonia

Pneumonia is a lower respiratory tract infection that causes the air sacs in the lungs to become inflamed and fill with pus or fluid. As inflammation gets worse, it can become harder to get oxygen into the bloodstream and the rest of the body — making it difficult to breathe.

Many germs can lead to a pneumonia infection, including bacteria, fungi or viruses such as influenza, RSV or SARS-CoV-2.

"This time of year, it's not terribly surprising to see an increase in pneumonia," said Dr. Eric Chow, chief of communicable diseases at Public Health — Seattle & King County. "But what a lot of people are talking about is, 'What are the specific causes?' And the increase of those specific causes is eye-opening."

Mycoplasma pneumonia, or M. pneumonia — the illness caused by the bacteria — is considered to be common, according to the CDC, which reports about 2 million such cases a year. But because there's no national reporting or dedicated surveillance system that tracks these infections, the actual figure is hard to confirm, the agency said.

These infections are generally mild and mostly feel like a cold, often allowing people to get out of bed and recover at home. Other bacteria, including Streptococcus pneumoniae, which typically lives in the upper respiratory tract, usually causes more severe illness, Chow said.

But any case of pneumonia can become serious and require antibiotics.

This year, Mary Bridge has seen more young infants and older children with pneumonia, even though providers typically mostly see kids between 2 and 4, Fairchok said. More kids are ending up in the ICU.

"Pneumonia is a great masquerader," Fairchok said. "It doesn't just infect the lungs, it can also infect other parts of the body."

The worst cases she's seen recently involve patients with not just fevers and coughing, but also brain inflammation, severe skin burns, and infections in eyes, mouth and genitals. For kids with Mycoplasma pneumonia, which Mary Bridge confirms through PCR testing, she's also seen a high rate of diarrhea and vomiting.

There's not yet a clear reason why pneumonia is surging this year. Many providers nationwide have theorized the spread of many pathogens slowed during the pandemic, when distancing, masking and hygiene practices were more widespread. Now that many people have put those measures behind them, some respiratory viruses are rebounding.

There's also been recent evidence COVID-19 infections can cause significant long-term changes to the immune system, which could help explain some long COVID symptoms or a weaker immune response, Fairchok said.

But these are all theories. "Nobody really knows exactly why" pneumonia in particular is on the rise this year, she said.

RSV & influenza

It's not quite another tripledemic, but RSV and influenza cases also are back and starting to take off.

Last week, Public Health — Seattle & King County confirmed the number of RSV-related emergency department visits had quadrupled from October to November. Since early November, the percentage of weekly ER visits linked to an RSV diagnosis jumped from about 0.14% of all hospital emergency visits to 0.86%.

The percentage of flu-related ER visits also skyrocketed from about 0.2% to 1.6%.

At Seattle Children's, staffers saw more than 80 cases of influenza A and over 150 cases of RSV two weeks ago, Zerr said.

"It's these really common viruses that are impacting many more people" than Mycoplasma pneumonia, she said.

In other parts of Washington, flu activity remains fairly low, though the percentage of positive lab tests for both RSV and flu have been climbing the past few weeks, according to the Department of Health.

Still, people shouldn't be too alarmed; in King County, RSV and flu levels align with what's typically expected this time of year, Chow added. But the data serves as a reminder that it's a good time to consider reupping infection prevention measures, he said.

"We expect flu and RSV to remain elevated for some time, if they're following similar patterns to previous years," Chow said.

COVID

The summer COVID surge that led to a significant bump in infection rates and emergency department visits largely subsided as the fall progressed.

In King County, both figures have dropped to lower levels than the county has seen since the beginning of pandemic, Chow said.

"COVID is in a lull," Fairchok added. "But, as we know, it does what it wants to do. There are definitely signs we're going back up again in other parts of the U.S. and the world, so we might see another surge there."

Chow agreed it's important not to let our guard down.

"The same precautions that we have been using for COVID are still important to protect us from infections related to other respiratory viruses," he said.

Whooping cough

Pertussis, also known as whooping cough, is another infectious disease health providers locally and nationwide have kept a close eye on this year.

It's been an unusually bad year for whooping cough, which often begins with common cold symptoms, including a runny nose and fever, but can lead to severe coughing fits that can last for weeks or months.

As of early December, state epidemiologists had counted about 1,800 cases to date. At that time last year, 70 cases had been confirmed.

About 82% of cases infected Washingtonians under 18, according to the state's most recent update. Nearly one-third are among children younger than 5.

"The good thing is that with pertussis, we do have means to prevent disease from happening, particularly for those at highest risk: young children," Chow said.

How to avoid respiratory infections

By now, most of us probably know how to stay healthy during times of high respiratory virus spread.

All the prevention strategies we used during the pandemic are still useful — and are especially key for people at higher risk of serious illness, including those who are older, immunocompromised or pregnant, said Dr. John Lynch, an infectious disease doctor at Harborview Medical Center. Washing hands, wearing masks, ventilating crowded indoor spaces, staying home while sick, and getting vaccinated remain effective ways to reduce transmission, Chow, Zerr, Fairchok and Lynch said.

Several health care facilities, including those in King, Snohomish and Pierce counties, recently brought back masking requirements for staffers as flu and RSV emergency department visits crossed transmission alert thresholds. Patients and visitors are encouraged to mask up when in health care settings until virus activity has dropped back down.

"People just need to recognize that every respiratory virus season is unique and can be very hard to predict," Lynch said. "In a bad respiratory virus season, we can see these cases end up in hospitals and ICUs. They can be quite serious."

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