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EL PASO COUNTY, COLO. -- As cold and flu season approaches, doctors issue a warning about whooping cough or pertussis.

They said it is on the rise across the country.

Pertussis is a contagious illness that is spread through sneezing and coughing.

It can occur at any age, although health professionals said it is most severe in infants and young children.

According to the Colorado Department of Public Health and Environment, 37 cases of whooping cough were reported in Colorado in a one week time span, from August 19 through the 25.

Health officials said that is a significant number.

"Of course it is important to get your infant immunized, but the message we are trying to get out now has to do with adult immunization," Dr. Bill Letson, Medical Director for the El Paso County Health Department, said.

Letson said that is because infants and children usually get the illness from a caregiver, such as a parent or grandparent.

"The reason for that is infants are more susceptible to having a severe form and perhaps dying," Letson said.

As we have seen, the number of pertussis cases are up across the country and in Colorado, where Dr. Letson said 763 cases have been reported since January first.

"El Paso County is not seeing an unusual increase in cases so far this year, but we are close to the metro area where there has been a substantial increase," he said.

State records show Adams County is leading the way with 127 cases to date.

That is 100 more than El Paso County, although experts said that may increase now that school is back in session.

"Pertussis comes in five to six year cycles, and it has been about five years since we had the last large pertussis outbreak in Colorado and around the country," Letson said.

He said pregnant women in their third trimester should also strongly consider getting vaccinated to get a head start on protecting their unborn.

The El Paso County Health Department has compiled a list of pertussis symptoms along with helpful information about the vaccine.

For those click here.