An old disease is making a big and deadly comeback as the country braces for its worst year for whooping cough in more than five decades.

The Centers for Disease Control confirms the disease is on the rise. At least nine people have died already this season.

"It can be fatal, but I probably hospitalize an infant a year," emergency room physician Dr. Nicholas Gentry said.

Doctors have treated an alarming 18,000 cases of  cases of pertussis, better know as whooping cough, this season. That is more than double what they saw last year.

The biggest reported outbreaks are in Arizona, Minnesota, New York, Washington, and Wisconsin.

Whooping cough is most dangerous to children, who should receive their first vaccination at two months old. Classic symptoms of the disease are a runny nose, a fever, and a severe cough.

"In between these episodes of severe cough, there is like a wheezing, trying to gasp for air," Gentry said.

The CDCl is investigating this year's spike. Doctors suspect shortcomings in the vaccine and an evolution in the bacteria that causes the illness. They're now urging adults to get vaccinated.

"If you're a new mom, a new dad, if you're a grandparent, if you're a caregiver and you're going to be seeing your niece or nephew who is under one, make sure you go and get your booster before you go for that visit. Every adult should do it," Dr. Siobhan Dolan, who treats patients at the Montefiore Medical Center, recommended.

CDC guidelines now recommend vaccinations for adults 65 and older and women more than 20 weeks pregnant.

The whooping cough attacks people of all ages, but it's most dangerous to children.