DENVER — The Centers for Disease Control says the U.S. is headed for its worst year of whooping cough in more than 50 years.

And Tuesday, new numbers for people infected in Colorado show no signs of the sickness slowing.

Colorado now has 940 official cases of pertussis—that number is the latest available from January to Sept. 22.

The week before, Colorado had 897 cases.

That adds up to 43 new cases in just one week.

And with fall and winter typically bringing higher counts, we could be on a record-setting pace for pertussis.

The worst recent year for whooping cough was in 2005 with more than 1,300 cases according to the Colorado Department of Health.

They are the sounds that soothe a mother’s heart. 10-week-old Jeremiah Damian fidgets and babbles in his mother, Valerie Castillo’s arms.

“It started off as a regular cold. Then, it started getting worse and worse,” says Castillo.

But the sound he didn’t make seven weeks ago, made her heart drop.

“I felt him stop breathing. I turned him over and he was purple, and limp,” she says.

Damian nearly died in August, when he stopped breathing because of highly-contagious whooping cough.

Doctors put him on a ventilator, feeding tube and oxygen—all for a preventable illness.

“It was horrible to see. He had everything hooked up to him. He wouldn’t open his eyes,” says Castillo.

Now, the Colorado Health Department says more children are getting infected with the bacteria.

Denver County has the highest with 152 cases so far this year.

Jefferson County is next with 146.

Adams County has 145.

And Boulder County shows 113.

“What we are seeing is a four- to five-fold increase,” says Dr. Rachel Herlihy, with the Colorado Department of Health.

And the state says the best way to protect your family is pertussis vaccination.

Dtap is for infants and young children. Tdap is for adolescents and adults.

“We know not very many adults get the vaccine. We know that from national estimates only eight percent get that vaccine,” says Dr. Herlihy. “Adults should receive it now if they haven’t received it,” she says.

Adults who are around children, including parents, grandparents, child care workers and teachers should be especially vigilant she says.

“I want everybody to get vaccinated. It’s kind frustrating when you hear people say they don’t believe in getting their kids vaccinated. That’s fine for you and your kids. But what about the kids they come into contact with?” questions Castillo.

Her son is a case in point. At three weeks old, he was too young to be vaccinated—and it almost cost him his life.

“It’s scary, it’s really scary. And there’s nothing you can do to prevent it. You don’t want to keep your kid sheltered from the world. If people get vaccinations it would save a lot of trouble,” she says.

Dr. Herlihy says the people who get infected most are infants and adolescents, ages 11 to 14 years old.

She also wants to remind parents to keep their child home at least five days after they’ve taken their last antibiotic.

They’re seeing some kids go back to school too soon and infect others.

Whooping cough information and resources