A highly contagious respiratory illness is on the rise in the United States this year.

Cases of whooping cough, also known as pertussis, have surged to pre-pandemic levels in 2024, according to the Centers for Disease Control and Prevention.

There's been over 17,500 cases of the nationally notifiable condition reported this year as of Oct. 5, according to CDC data. The CDC says that figure is more than five times higher than the number of cases reported at the same time in 2023. It's also substantially higher than the 10,879 cases reported at the same time in 2019, and the most since 2014.

So what exactly is whooping cough? And why are cases suddenly on the rise? Here's what to know:

What is whooping cough?

The CDC defines whooping cough as a very contagious respiratory illness caused by a bacteria called Bordetella pertussis. The bacteria attach to tiny, hair-like extensions called cilia that line part of the upper respiratory system and then release toxins, damaging the cilia and causing airways to swell.

How does whooping cough spread?

Whooping cough can spread easily from person to person, according to the CDC. The bacteria that causes the illness gets released into the air through coughing and sneezing.

Those who contract whooping cough can spread the illness once symptoms start and up until at least two weeks after coughing begins, per the CDC.

Why are whooping cough cases on the rise?

The CDC says it's likely that mitigation measures utilized during the COVID-19 pandemic, like masking and remote learning, led to a decrease in the transmission of whooping cough.

Why is it called whooping cough?

A common symptom of pertussis is a "whoop" noise that occurs when someone inhales following a coughing fit, according to the CDC.

What are the signs and symptoms of whooping cough?

It could be a while before those coughing fits begin, though. The CDC says early symptoms usually appear five to 10 days following exposure, but it could take as long as three weeks for them to develop.

Early symptoms are similar to a common cold, can last for one to two weeks and typically include a:

• Runny or stuffed-up nose
• Low-grade fever (lower than 100.4 degrees Fahrenheit)
• Mild, occasional cough

Coughing fits could begin one to two weeks after the initial symptoms show, the CDC says. The coughing fits typically last one to six weeks, but can remain for up to 10 weeks.

The coughing fits generally become worse and more frequent over time, and they can cause people to:

• Make a high-pitched "whoop" when they inhale after a coughing fit
• Vomit during or after coughing fits
• Feel very tired after the fit, but usually seem well in-between fits
• Have difficulty sleeping at night
• Struggle to breathe
• Fracture a rib

"Those who get these coughing fits say it's the worst cough of their lives," the CDC says.

It's important to note that many babies with whooping cough don't actually cough at all. The CDC says babies may instead experience life-threatening pauses in breathing called apnea, or pneumonia.

Does whooping cough go away on its own?

The CDC says it's very important to treat whooping cough early and before the coughing fits begin. Early treatment could make the illness less serious and help prevent the spread of it.

In most cases, whooping cough can be managed at home by:

• Taking antibiotics exactly as prescribed by your healthcare provider
• Keeping your home free from things that cause coughing like smoke, dust and chemical fumes
• Using a clean, cool mist humidifier to loosen mucus and soothe the cough
• Eating small meals every few hours to help prevent vomiting
• Getting plenty of fluids, including water, juices, and fruits

The CDC instructs those with the illness not to take cough medicine unless recommended by a healthcare provider.

Hospital treatment may be required for those who develop serious symptoms or complications.

Who's at higher risk for severe whooping cough cases?

Babies younger than 1 year old are at the greatest risk of getting whooping cough and suffering from severe complications, per the CDC. That age group also experiences the highest rate of whooping cough. The CDC says about one third of babies younger than 1 who contract the illness need hospital treatment.

Those with pre-existing conditions that may be worsened by whooping cough, such as immunocompromising conditions, are also at high risk of developing a serious case of the illness, according to the CDC.

Is there a whooping cough vaccine?

Yes, and the CDC recommends it for people of all ages, as it's the best way to prevent the infection. The whooping cough vaccines work well but protection fades over time, according to the CDC. Those who get the illness and are vaccinated tend to develop milder cases.

What is the whooping cough vaccine called?

There are two types of combination vaccines that offer protection against whooping cough, diphtheria and tetanus, according to the CDC. Children under the age of 7 receive the DTaP vaccine, while those 7 and older get the Tdap vaccine.

The CDC recommends pregnant women get the Tdap vaccine early in the third trimester of each pregnancy to protect babies from the illness in the first few months post-birth. The vaccination during pregnancy prevents nine in 10 babies from being hospitalized with whooping cough, per the CDC.

Adults getting the Tdap vaccine for the first time should get a booster dose at least once every 10 years, according to the CDC.

What are the side effects of the whooping cough vaccine?

The CDC says most people who get a whooping cough vaccine don't experience any serious side effects. The potential side effects tend to be mild and go away within a few days.

The mild side effects of the DTaP vaccine include swelling/soreness where the vaccine was given, fever, irritability, feeling tired, loss of appetite and vomiting, per the CDC. The Tdap vaccine, meanwhile, can lead to pain/redness/swelling where the vaccine was given, mild fever, headache, feeling tired and nausea/vomiting diarrhea/stomachache.

You can check out more information on whooping cough vaccines here.