DENVER (CBS4)- Health officials claim the U.S. is on track for its worst year for Whooping Cough in more than 50 years. There’s also an increase in Colorado.

Whooping Cough or Pertussis, is a highly contagious bacterial disease. It causes children to make a whooping sound as they cough and gasp for breath.

In rare cases it is deadly. The Centers for Disease Control reports that nine children have died of Whooping Cough so far this year.

Nearly 18,000 cases have been reported nationwide since January.

CBS4 Medical Editor Dr. Dave Hnida said it’s important for parents to remember they must get vaccinated as well as their children.

RELATED LINK: Dr. Dave’s Blog

“The biggest issue isn’t little kids not being immunized, it’s adults not being immunized. They get the disease, they don’t get that sick, they wind up getting in contact with the infant and the infant winds up getting terrifically sick,” said Hnida.

Hnida also said the vaccine was reformulated in 1997 and isn’t effective for a long period of time.