State health officials said Tuesday that reports of whooping cough disease have reached epidemic levels in Washington.

A total of 640 cases have been reported through March 31. That’s well beyond the 94 cases reported during the same time period a year ago.

Health officials are encouraging children and adults to get vaccine shots.

Twenty cases of whooping cough that have onset dates in 2012 have been reported in Kitsap County. The number is even higher when cases from January, with onset dates in December, are included in the total.

“We’re looking at 25 cases in the last four months,” said Siri Kushner, an epidemiologist with the Kitsap Public Health District.

“Of those, nine have been Bainbridge Island residents,” she said.

Epidemiologists are basically disease detectives, and Kushner said her review of the statistics show that the vast majority of the cases of whooping cough in Kitsap County — 84 percent — involve patients between the ages of 1 and 18.

The number of reported cases in the county easily exceeds the total seen in 2011.

Sixteen cases were reported last year.

“Pertussis in general has a cyclical nature, where it peaks every three to five years.  It’s possible that if this trend continues, we could reach or surpass our peak in 2010 and the peak we had in 2005,” Kushner said.

In 2010, 29 cases of whooping cough were reported in Kitsap County; 49 were reported in 2005.

So far this year, the hardest hit counties have been Snohomish (168 cases), King (88), Pierce (78) and Clark (42).

Whooping cough is a highly contagious respiratory illness that is spread by coughing and sneezing.

Health experts said the disease affects people of all ages but is most serious in infants, especially those too young to get vaccinated or who aren’t fully protected.

Pertussis causes cold-like symptoms and is followed by a long, severe cough that can last for weeks.

“We’re very concerned about the continued rapid increase in reported cases,” said Washington Secretary of Health Mary Selecky.

“This disease can be very serious for young babies, who often get whooping cough from adults and other family members. We want all teens and adults who haven’t had Tdap to be vaccinated to help protect babies that are too young for the vaccine,” she said.

Information on preventing whooping cough is available on the Department of Health website.