PHILADELPHIA — Pennsylvania has seen more cases of whooping cough than any other state this year, with 2,165 cases of the serious bacterial infection reported as of late September.

At this time in 2023, the state had reported 205 cases to the Centers for Disease Control and Prevention. This year's cases represent a 956% increase from the year before.

The continued outbreak prompted a statewide alert from health officials in early September, and the Children's Hospital of Philadelphia re-instituted staff masking policies this summer to better protect employees and patients.

Whooping cough, or pertussis, is caused by a bacterial infection and can result in a severe cough that lasts for months. It's particularly dangerous for infants, especially those too young to be vaccinated against the disease.

Preventative measures for whooping cough at CHOP

In August, seeing a rise of cases at its offices in Philadelphia's collar counties, CHOP began requiring staff to mask in waiting rooms and while seeing patients in Montgomery, Chester, Bucks, and Delaware Counties in Pennsylvania and Burlington County in New Jersey.

At the end of September, with cases also rising in Philadelphia, CHOP staff began masking at their city facilities as well, said Erika Hayes, CHOP's senior medical director of infection prevention.

"During the COVID-19 pandemic, we all got very, very good about not going out when we were sick and wearing our masks," she said. "Mid-2020 to about late 2021, the number of pertussis cases were vanishingly rare, and it was because of these good practices."

The health system is hoping that requiring staff to mask now can help slow the flow of cases.

In a statement, the state Department of Health said areas with high population density like Philadelphia and Pittsburgh are seeing the highest increases. Still, pertussis cases in Philadelphia have not been evenly spread among health providers: St. Christopher's Hospital for Children in Kensington has seen only a handful this year. CHOP has seen 609 across its facilities in the region.

Hayes said she hoped cases might decrease soon. "But honestly, especially with the kids back in school, I am very worried that we may continue to rise," she said.

Most of the pertussis outbreaks reported this year took place at middle schools, high schools, and colleges, state officials said. Montgomery County's Plymouth Whitemarsh High School reported a pertussis outbreak among six students in April.

New Jersey also saw higher-than-usual whooping cough cases this summer, prompting an alert from the state health department, although the cases reported so far this year are now lower than year-to-date case counts from 2023. And the state is seeing far fewer cases than neighboring Pennsylvania, with just 128 cases reported this year.

What's driving the rise in pertussis cases?

At Virtua Health in South Jersey, infection prevention officer Martin Topiel said the health system is seeing more whooping cough cases in its ERs and urgent care centers than usual.

But it's unclear what exactly is behind the rise. Topiel said that better detection methods could contribute to an increase in reported cases.

Some patients also put off vaccinations during the COVID pandemic, Hayes noted, adding that the standard childhood Tdap vaccine, which protects against tetanus, diphtheria, and pertussis, wears off as you age. That might have put more patients at risk.

"People can become susceptible again to pertussis, and pertussis in adults and grown-ups looks like a little bit of a cold and then a cough that won't go away for a long time," she said. "A lot of people don't get diagnosed. But it's extremely contagious."

Newborns are at the highest risk of infection and, in rare cases, death from pertussis. In very young babies, the symptoms of whooping cough might be more difficult to spot, since producing the distinctive "whoop" requires muscle tone not yet developed. Instead, they may struggle to breathe or stop breathing.

Preventing serious illness

That's why it's especially important for adults and older children to stay up-to-date on Tdap boosters — to protect babies under two months, who are too young to be vaccinated, Hayes said. It's also important for pregnant people to receive a Tdap shot between 27 and 36 weeks gestation of each pregnancy, state officials said, in order to give newborns some added protection.

State officials said 94.6% of Pennsylvania's kindergarteners are vaccinated for pertussis. And 92.4% of 7th graders and 97.1% of 12th graders have gotten a Tdap vaccine.

Patients can still get ill from pertussis if they're vaccinated, but the vaccine can prevent more serious outcomes, said Topiel.

"Pertussis can last a very long time and it can be quite disabling and uncomfortable once someone catches it," he said. "I don't want people to go through that."

'Vaccines are our best defense'

Earlier this summer, Emmani Osborne-Morrison came down with a cold. Emmani has a severe form of epilepsy, and her mother Juliette Osborne, a nurse practitioner from Lumberton, N.J., closely monitors her health.

"She was fatigued, not herself, not eating — I couldn't make out what it was. I thought it might be chronic sinusitis. But then one night she started coughing," Osborne said.

Emmani coughed for four hours straight, and Osborne got in touch with her primary care physician and was told to take her daughter immediately to the emergency room. There, she tested positive for whooping cough.

The family quarantined and took preventative antibiotics to prevent the infection from spreading through the household. Emmani was over the worst of it in about two weeks, her mother said, likely because she had been vaccinated.

Osborne advised parents to make sure their kids are vaccinated, too — and to watch out for unusual cold symptoms they might otherwise miss.

"It was very crazy hearing that she had whooping cough when she had already been vaccinated," Osborne said. But, she said, "vaccinations are our best defense. I believe Emmani's vaccine helped reduce or shorten her symptoms."

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