SEATTLE — The number of pertussis — whooping cough — cases in Washington has risen to more than 500 cases and will likely set a record in 2012, a state Health Department spokeswoman said.

The outbreak is likely to exceed the number of about 950 cases last year and the previous record of about 1,020 in 2005, said Michele Roberts, immunization program health communication manager.

“We are really concerned about this,” she said.

Figures released Tuesday show there have been 549 cases of pertussis through March 24. That’s up 86 cases in a week. At this time in 2011 there were 88 cases in the state for the year.

There are several possible reasons for the recent increase in cases, Roberts said.

The disease is cyclical, and the vaccine most people get as children is not permanent. Rising awareness of the disease leads some adults to find out what they thought was a nagging cold and persistent cough is pertussis.

Pertussis has reached epidemic levels locally in six counties — Jefferson, Cowlitz, Kittitas, Snohomish, Skagit and Whatcom, Roberts said. There are 18 counties in Washington where pertussis has not been reported, but that doesn’t mean they are disease-free. It’s estimated only 10 to 15 percent of pertussis cases are reported.

The coughing spells are most serious in infants. Of the 37 babies who have had whooping cough these years in Washington 12 have been hospitalized, Roberts said.

There have been no pertussis deaths this year in Washington. Two babies died in 2011 and two babies in 2010.

“Some are very young — a month,” Roberts said. “It’s very tragic.”

Only about 10 percent of adults are immunized. They typically get the vaccine combined with a tetanus booster shot.

“You can help stop spreading disease in the community to prevent the disease in babies,” she said.

For children, a series of four shots is recommended, starting in the first 18 months and ending before entering kindergarten, the state Health Department says on its website. The pertussis vaccine is usually combined with diphtheria and tetanus vaccines.

Whooping cough gets its name from the sound of a coughing fit that makes it hard to breath. The coughing also can make it hard for a child to eat or drink. Vomiting can follow a long coughing spell.

The disease can cause pneumonia, brain damage and death, the state website states. Pertussis is treated with antibiotics.

The outbreak in Cowlitz County has led one Longview hospital to take special precautions.

PeaceHealth St. John announced Monday that patients showing symptoms — runny nose, low-grade fever and cough —may be placed in isolation. Visitors and workers displaying symptoms may be asked to leave.

Nationally the number of cases has been rising since the mid-2000s.

The Centers for Disease Control and Prevention says pertussis is common in the United States, with epidemics every 3 to 5 years. There were 27,550 cases of pertussis reported in 2010.