Whooping cough cases in California and Orange County continue to rise, and on Friday state public health officials said the illness has again become an epidemic.

As of last week, 3,458 cases of pertussis, or whooping cough, have been reported to the state Department of Public Health in 2014, more than the total for last year. In the last two weeks, more than 800 cases have been reported.

In Orange County, Health Care Agency spokeswoman Nicole Stanfield said there have been 98 cases, including 22 infants.

“Preventing severe disease and death in infants is our highest priority,” Dr. Ron Chapman, state health officer, said in a statement. “We urge all pregnant women to get vaccinated. We also urge parents to vaccinate infants as soon as possible.”

Babies can be vaccinated as young as 6 weeks and pregnant women should be vaccinated during their third trimester to pass some protection to their newborns.

The state said pertussis is cyclical and peaks every three to five years. The most recent peak was in 2010 when 10 babies died in the worst outbreak in 50 years. This year, two infant deaths have been reported.

For children, a typical case of pertussis starts with a cough and runny nose for one to two weeks, according to the state’s description of symptoms. The cough then worsens and children may have rapid coughing spells that end with a “whooping” sound. Young infants may not have typical pertussis symptoms and may have no apparent cough. Parents may describe episodes in which the infant’s face turns red or purple. For adults, pertussis may simply be a cough that persists for several weeks.

The recent outbreaks have been attributed to a change in the vaccine.

Research after the 2010 pertussis outbreak found that the vaccine offers less protection after changes were made in the 1990s to reduce side effects. The original vaccine, developed in the 1940s, could cause fever as well as pain, redness and swelling at the injection site and, on rare occasions, seizures.

Contact the writer: 714-796-3686 or cperkes@ocregister.com