DENVER (AP) – Colorado is having its worst whooping cough season in at least six decades.

As of Dec. 8, 1,407 cases of whopping cough have been reported in Colorado, the Colorado Department of Public Health and Environment said Tuesday. That’s the highest number on record since 1948, when there were 1,833 cases.

An older adult from Larimer County died of the highly contagious disease in October, the first whooping cough death Colorado since 2005, when two infants died.

Whooping cough, officially called pertussis, gets its name from the sound those afflicted with it make when they gasp for breath.

It has made a resurgence across the country, and 2012 is on track to be the nation’s worst for whooping cough since 1959.

Health experts aren’t completely sure why cases are increasing, but one possible reason is that the current vaccine against the disease, introduced in 1997, doesn’t provide immunity for as long as the previous version, said Dr. Rachel Herlihy, immunization director at the state health department. Cases also seem to spike every three to five years and, with the last busy whooping cough year in 2005, Herlihy said officials had been expecting another increase.

The health department recommends that adults and children get the whooping cough booster vaccine, Tdap, when they get their annual flu shot. Besides protecting themselves from the disease, immunized adults can prevent the disease from being spread to children, Herilhy said.

“This is an important vaccine and not just for kids and babies, but adults too,” she said.

Under the new federal health care law, people with insurance can get a free whooping cough shot from their doctor. People without insurance may be able to get a low-cost immunization at local public health agencies.

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