Whooping cough cases more than 3 times higher than last year in return to pre-pandemic levels

Cases of whooping cough are more than three times higher this year than they were at the same time last year, according to data from the Centers for Disease Control and Prevention (CDC).

So far this year, there have been 10,865 recorded cases of whooping cough, or pertussis, compared to the 2,918 recorded during the same time in 2023, CDC data shows.

The number of cases is closer to the 8,271 cases of whooping cough recorded this time in 2019, indicating a return to pre-pandemic levels.

Doctors said that reported cases of whooping cough were lower than usual over the past few years, likely due to COVID-19 mitigation measures including masking, remote learning and social distancing.

"During the pandemic itself, we really had a low point in transmission of pertussis, and that was just because of all of the social distancing and isolation," Dr. Mike Patrick, an emergency medicine physician at Nationwide Children's Hospital in Columbus, Ohio, told ABC News. "If kids aren't around each other, and also around adults, then they're not able to pick up the disease, since it's an infectious disease and transmitted from one person to another."

"So, I think, we're just getting back up there because people are back doing the normal things that we do, and that's just the pattern that we see with the vaccine that we have. But I will say, without the vaccine, we'd see a whole lot more pertussis than 10,000 cases," he added.

Dr. Lori Handy, an attending physician in the division of infectious diseases at Children's Hospital of Philadelphia, said the uptick in cases of whooping cough post-pandemic is similar to those seen in the U.S. with other diseases as mitigation measures started to disappear.

"I honestly think it was a little surprising that it took this long, recognizing we lifted [many] measures close to two years ago," she told ABC News. "I think many folks remember the increase in RSV cases that we saw back in 2022, so this has lagged behind some other respiratory infections, but definitely now has resurfaced and looks very typical to 2019."

Whooping cough is a very contagious respiratory illness caused by a type of bacteria called Bordetella pertussis.

These bacteria attach to the cilia -- the tiny, hair-like structures found on the surface of some cells --of the upper respiratory system that help clear mucous and other debris in the airway, and release toxins. The toxins damage the cilia and cause the upper airways to swell, according to the CDC.

"You get airway swelling and a terrible, terrible cough because the cilia aren't working, and so your body resorts to coughing to try to keep stuff out of the lungs and to bring things up," Patrick said. "Oftentimes, babies will have a little bit difficulty breathing. They're having the cough…and then they take a big, deep breath, because they hadn't breathed during all those coughs, and that's why it's called whooping cough, because that's the [sound] when they're coughing."

Whooping cough is spread from person-to-person through coughing and sneezing. Infected people can be contagious for weeks without knowing they have whooping cough.

Early symptoms often resemble a common cold -- runny nose, cough and low-grade fever -- and typically last for one to two weeks. Symptoms, however, can progress to rapid, violent coughing fits that can last up to 12 weeks.

Whooping cough can be treated with antibiotics and receiving treatment early can reduce the severity of the infection. Most whooping cough symptoms can be managed at home, according to the CDC.

Although anyone can contract pertussis, infants under age one, pregnant women and immunocompromised people are at highest risk for severe illness.

"In the younger kids, and especially in infants, they can have apnea, so they stop breathing. They can be hospitalized in the intensive care unit, and unfortunately, children can and have died from pertussis," Dr. Robert Frenck, a professor of pediatrics in the division of infectious diseases at Cincinnati Children's Hospital in Ohio, told ABC News. "So, these are not innocuous infections. They can be very serious, and they can be deadly."

A vaccine for whooping cough was introduced in the late 1940s and the number of cases each year has since dropped dramatically, decreasing more than 90% compared to the pre-vaccine era.

Before the vaccine, there were an estimated 200,000 cases annually among children and up to 9,000 children died, according to the CDC.

There are two types of vaccines currently used to protect against whooping cough: diphtheria, tetanus, and pertussis (DTaP) vaccine for babies and children younger age 7 and tetanus, diphtheria, and pertussis (Tdap) vaccines for older children, adults and pregnant women.

A recent report from the CDC found that exemptions for routine childhood vaccination among kindergartners during the 2022-23 school year were at the highest level ever, including for the DTaP vaccine. Frenck said the increase in whooping cough cases are a reminder that vaccines are effective, but said he doesn't discourage vaccine-hesitant patents from asking questions.

"Parents want to do what's best for their children, and so they want to keep their children healthy," he said. "Unfortunately, there has been a fair amount of misinformation about vaccines to where people are confused. So, my recommendation really is to talk with your health care provider, ask your questions, get your answers, feel comfortable about having your children vaccinated. Vaccines are well-tested, vaccines are safe, vaccines are protective."

Handy said she also encourages everybody who is eligible to get vaccinated and for health care providers to be on the lookout for pertussis cases

"For health care providers ... recognize this is back, like five years ago, and the only way we will detect it is by testing it and then using our public health measures to prevent spread," she said.