EVERETT – Public health officials say they’ve seen “an explosion” of whooping cough cases in Snohomish County and are urging people, especially pregnant women, to get vaccinated.

Forty cases have been confirmed this year, said Dr. Gary Goldbaum, health officer for the Snohomish Health District. That’s nearly double the 23 cases reported during all of last year.

“There’s been an explosion over the past month — 30 out of the 40 cases,” Goldbaum said. “That’s why I’m especially concerned that the rate of increase is very quick.”

Goldbaum said he can’t predict how quickly whooping cough will continue to spread. “I’m hoping that Snohomish County will be spared another epidemic,” he said.

The last big outbreak of whooping cough was in 2012, when 585 people were infected locally, part of a statewide epidemic.

It’s especially important for any adult in contact with young children, particularly newborns, to get vaccinated, Goldbaum said. It’s the only protection for newborns, who are too young to be vaccinated against the disease, he said. “That’s also why we recommend every pregnant women should be vaccinated with every pregnancy.”

The shot is recommended for women when they reach the 28th week of their pregnancy

Most of the local whooping cough cases are being diagnosed among school-aged children, Goldbaum said, in part because adults tend to just put up with a nagging cough and don’t go to the doctor for a diagnosis.

Six school districts — Lake Stevens, Arlington, Everett, Snohomish, Mukilteo and Marysville — have reported at least one case, said Heather Thomas, a Snohomish Health District spokeswoman.

Cases also have been reported at Everett Community College, among participants in children’s sports clubs in Snohomish and Mukilteo, and a day care in Everett, Thomas said.

The recent surge in local whooping cough cases is being reported elsewhere in Washington. Statewide, 319 cases have been reported this year, compared to 49 during the same period last year, according to the state Department of Health.

Whooping cough is a highly contagious disease caused by a bacterial infection. It affects the respiratory system and is spread by coughing and sneezing.

The immunization is recommended for infants at 2 months, 4 months, 6 months and 15-18 months of age. Another shot is recommended when children are between 4 and 6 years old and between 11 and 12 years old.

All adults who have not been vaccinated should get one dose, Thomas said. The vaccine protects against whooping cough, diphtheria and tetanus.

Vaccinations are widely available at doctor’s offices and non-profit clinics.

Sharon Salyer: 425-339-3486 or salyer@heraldnet.com.