Whooping cough cases are up in Illinois and across the country, the CDC warns.As of the end of September, reported cases in the state are nearly five times higher than they were this time last year, according to data from the U.S. Centers for Disease Control and Prevention. Whooping cough, also called pertussis, is a highly contagious respiratory disease that spikes in the fall alongside other diseases like RSV, the flu and COVID-19.The bacterial infection initially presents as a standard cold for the first week or two, said Dr. David Nguyen, an internal medicine physician at Rush University Medical Center.As time goes on, the cough gets worse and can last for several weeks. The coughing fits tend to last for about five to 10 coughs and when the person catches their breath, the breath sounds like a whoop, Nguyen said.Babies are especially vulnerable to whooping cough — one in three require hospitalization due to the disease, according to the CDC."The real danger is in babies, especially young babies under 6 months. They have smaller lungs and less reserves so they might end up having complications and stop breathing," said Nguyen, who also specializes in infectious diseases in kids.If the baby stops breathing, they're at a serious risk for heart problems, Nguyen said. That's when whooping cough can be fatal. Related Severe obesity is a health crisis Americans can’t ignore CDC might drop 5-day COVID-19 isolation guideline — prompting mixed feelings in Chicago expert The disease can also seriously affect kids, teens and adults. It's recommended adults get the Tdap vaccine booster every 10 years, which protects against tetanus, diphtheria and pertussis. Pregnant people should also get the vaccine to boost their baby's immune system and protect them in their first few months of life, Nguyen said. For babies, the first dose of DTaP is given at two months and boosters are administered throughout childhood.As of Sept. 21, 1,058 cases of whooping cough have been reported in Illinois this year, according to CDC data. At the same point last year, there were only 230 cases reported.The spike in cases is likely because kids and adults are not up to date on their vaccinations, Nguyen said. That could be because people are refusing vaccinations for themselves and their kids or because people skipped visits to their primary care doctor during COVID lockdowns. "One big reason rates go up is when vaccination rates go down," Nguyen said. "It's important not just for the baby to be vaccinated, but for everyone in the household to be up to date on vaccines."For both kids and adults with whooping cough, Nguyen recommends seeking medical help if the cough gets more severe and the person is struggling to breathe or throwing up because of the cough.