"It is highly contagious," Lora Werner, the deputy director of the Delaware County Health Department, told Action News. "What we will find is someone who is diagnosed with whooping cough, about 100 percent of their household contacts will get it from them if they are not vaccinated."
Werner said Delaware County has seen about 20 cases of whooping cough since the start of the year. She said 75% of those cases have been in young boys around the age of 15.
Whooping cough is caused by a bacteria spread through the air when an infected person coughs or sneezes. The main symptom is a severe cough.
READ MORE: Health officials investigating increase in whooping cough cases among children in Montgomery Co.
"This cough is kind of particular. It's very, very intense. Very often, people have a very hard time catching their breath in between," said Dr. Richard Lorraine, the medical director in Montgomery County.
Health officials say the only way to confirm you have whooping cough is to get a diagnosis.
"The only really official way to tell is to get tested in a doctor's office, and they will do a respiratory panel and diagnose it," Werner explained.
Werner said it is common for whooping cough to spread among young people, especially in a school setting.
"It happens every three to five years across the globe that we see these cycles of cases coming up and going down again, and this age group is the one it's most noticeable with," she said.
In Chester County, health officials have identified an outbreak in schools. They say more than 25 cases, affecting multiple districts, have been reported. Officials said they also expect the number of cases will increase.
Montgomery County officials say the county is also seeing a rise in cases, primarily among high school students.
"There's a chance that some of them may have not gotten their booster at the 11 to 12-year-old range, in which case their immunity level would be somewhat lower," Dr. Lorraine said.
Dr. Lorraine said the best way to protect yourself is to get vaccinated, but he said research shows antibody levels drop over time.
Lorraine suggests people educate themselves about the illness, but he said at this time there is no reason for anyone to panic about the number of cases reported in the county.
"There hasn't been any signal to us at this point that this is outside of those normal bounds, just it happens to be one of those times when we're seeing more cases," he said. "I'm not reading too much into the fact that we are seeing a few more cases right now, nothing more than just normal variation that we see."