Emergency medical technician Kit Ho was happy to get a shot for pertussis, also known as whooping cough, Saturday because it’s been "a while."

"A very big mosquito bite," said Ho, 20, about the shot in her upper left arm while at a paramedic facility on Young Street.

She was the first of about 25 workers from the city’s Department of Emergency Services who will receive a free pertussis immunization shot this week.

While Honolulu is not seeing a significant increase in the disease, health officials are concerned about a recent spike in the illness on the mainland and want to remind residents to get vaccinated, said Dr. James Ireland, director of the Department of Emergency Services.

Washington state, which has seen a 1,300 percent increase in cases, declared a whooping cough epidemic in April, and 37 states have reported an increase in the disease this year, according to the Centers for Disease Control and Prevention.

More than 20,000 cases had been reported so far, placing the country on track to reach the highest number of cases since 1959, when 40,000 illnesses were reported, the CDC says.

"The best way to prevent an increase in cases here is to make sure people are up-to-date on vaccinations," Ireland said. "If it’s been more than 10 years since a booster for pertussis you really should get one, not only to protect yourself, but your family and friends."

Whooping cough is highly contagious and can be deadly, especially for infants, the CDC said. The illness is known for uncontrollable coughing fits that can lead to a whooping sound as the person tries to catch his breath. The cough can last for months.

Ireland said the disease most seriously affects the young. Antibiotic treatment is available after infection, but the best protection is to be vaccinated, he said.

He suggested people check with their health insurance carrier for the cost of a shot after insurance. The shots can be given without a prescription, simultaneously with a tetanus booster, and at some pharmacies. Ireland said the shots can cause soreness and, less commonly, allergic reactions.

The Department of Emergency Services already recommends its 180 or so first responders get vaccinated, but first offered a free vaccination to workers in 2010 after a baby died in Hawaii from whooping cough. At that time, about 65 paramedics or emergency medical technicians received the vaccine.

This year, about 25 employees will get free shots, which cost the city about $50 each.

"When people are sick and they call the ambulance, these are the guys who come," Ireland said. "We want to protect them."

Ho, who became an EMT in March, said she wanted to be immunized because she doesn’t want to be the one to spread the disease to her patients or her family.

"Who knows what kind of patients I’ll get," she said.

A spokeswoman for the department said the city didn’t have to pay for the vaccine this year because the shots are left over from a batch bought for employees in 2010.