SAN DIEGO — San Diego County’s public health department warned local doctors Friday that the region is in the midst of a significant increase in walking pneumonia cases, especially among children ages 2 to 4, echoing a national trend recently observed by the U.S. Centers for Disease Control and Prevention. And this surge has not arrived alone. Whooping cough is also making a significant appearance this fall.

The county health department warned Thursday that the region has recorded 547 confirmed and probable whooping cough — also called pertussis — cases so far this year, compared to 332 cases in all of 2023, with the majority of cases affecting those age 11 to 17. But the numbers have been even more eye-popping for walking pneumonia, which is caused by the bacteria mycoplasma pneumoniae.

Characterized by a high fever, cough, sore throat, headache and fatigue, walking pneumonia diagnosis in local emergency rooms jumped fourfold from Oct. 19 to Nov. 2, spiking from 0.2% to 0.8% of all diagnoses for children aged 2 to 4. A similar jump, though not quite so high, was observed for children and adolescents aged 5 to 17.

Generally, this type of pneumonia is less severe than other forms and is thus given the moniker “walking” as it is less common to cause hospitalization. But that has not been the case with the current increase in cases.

Rady Children’s Hospital reported a massive rise in walking pneumonia admissions, with 92 kids ending up in hospital beds so far this year compared to just 13 in all of 2023 and eight in 2022. Positive test results have also increased significantly from 61 last year to 532 this year.

Whooping cough cases have also risen from 57 last year to 211 at Rady this year, but the hospitalization rate has been much lower with just three admitted in 2024.

It is, noted Dr. Alice Pong, an infectious disease specialist at Rady, a very cough-heavy moment in hospitals.

“Some of it is pertussis, some of it is mycoplasma, some of it is caused by other viruses, and we are starting to see flu,” Pong said. “I think in the next month or two we’re just going to continue to see more respiratory illnesses.

“That doesn’t mean everybody needs to go into quarantine or anything, but they need to just be smart, you know, and take precautions — wash their hands, if you have immune system issues, avoid large crowds.”

Kids who are having trouble breathing, Pong said, should see a doctor.

“If they have a persistent cough and a fever, if they’re having trouble breathing, they should be taken to their pediatrician and be seen, especially if it has been going on for three or four days and it’s getting worse,” Pong said.

The county health department’s examination of recent emergency department data shows much lower walking pneumonia levels for adults. However, Dr. Erik Berg, interim medical director of the county’s epidemiology and immunization services branch, said Friday that such numbers can be misleading. That’s because doctors are much less likely to order the kind of confirmatory testing necessary to determine what kind of pathogen is causing an adult’s pneumonia symptoms.

“Typically, adults are not going to be tested for mycoplasma specifically,” Berg said. “Standard practice for adults in the (emergency department) who have pneumonia is empiric treatment or just prescribing antibiotics to cover bacteria including mycoplasma.”

Scripps Health reported an increase in positive mycoplasma pneumoniae tests recently with nearly 40 recorded in October compared to less than 10 in September. Twenty positives have already been documented in November. It was not clear how many of those were in adults.

Tri-City Medical Center in Oceanside and Paradise Valley Hospital in National City both said they have not observed similar increases.

Of the two threats, pertussis is vastly more preventable, as there has been a vaccine available for decades that can significantly reduce the chances of severe illness for those who become infected. But babies remain by far the most vulnerable.

The DTaP vaccine protects against diphtheria, tetanus and pertussis, but the first dose of a five-dose series is not administered until a newborn is two months old, with additional shots at four months, six months, 15 to 18 months and four to six years.

This means there is a two-month window after birth where neonates are at their most vulnerable. Pregnant mothers are strongly advised to receive a pertussis booster shot in their third month of pregnancy, allowing their immune systems to generate protective antibodies that transfer to their babies across the placenta before birth, delivering a significant measure of protection to bridge the distance until the vaccine can be given.

But many are not taking their doctors up on the offer. A county survey showed that only about 58% of San Diego County women received the Tdap — the adult version of the vaccine — during pregnancy, a number that fell to just 53.4% in 2022.

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