SKOWHEGAN — The number of cases of the highly contagious disease whooping cough continues to rise statewide — as do the ages of those affected.

What was first reported in May as a handful of cases among mostly young children, is now being reported among men and women over 40, according to Dr. Sheila Pinette, director of the Maine Center for Disease Control.

“We usually see cases in children, but some people, especially adults, do not keep up so well on their vaccinations, so they’re going to have a higher chance of getting it,” Pinette said Monday. “Adults usually tolerate it much better than children.”

There have been 347 confirmed cases of whooping cough in Maine since January, up from 265 cases reported as of July 19, Pinette said. There were just 79 cases of the disease in Maine at this time last year, she said.

Of confirmed cases statewide, 17 people were in their 40s, four were in their 50s and five were 60 and older.

“Even if you are vaccinated as an adult, there is some waxing and waning of immunity of a vaccine — it’s still effective, but not as much as it would be if you had received a vaccine,” Pinette said.

Pinette said Somerset County has had 85 confirmed cases of pertussis since January. Cumberland County in the southern part of the state, was the highest with 99 cases as of Monday.

Penobscot County is third in the state with 47 confirmed cases.

Whooping cough, the common name for pertussis, is a contagious respiratory disease that can cause long, violent coughing fits and the characteristic whooping sound that follows when a person gasps for air. The disease can have severe complications for infants, pregnant women and people with respiratory conditions.

Pinette would not be more specific about the cases of whooping cough among people 40 and older because the relatively small numbers increased the chance of identifying affected people locally.

Pinette said it is not unusual for adults to contract the disease, especially if they have come into contact with small children or others who have been exposed to the disease.

Pinette recommended booster shots for adults and for children entering middle school. She said people who are not immunized against the disease have an eight times higher risk of contracting whooping cough than those who get vaccinated.

Letters alerting families to the presence of whooping cough were sent home with Skowhegan high school students May 10. There were three cases reported at first — two at the high school and another at an elementary school.

More cases were reported in the weeks that followed, mostly among 11-19 year olds, including in towns outside of the Skowhegan school district. Summer camp operators were alerted to the “mini-epidemic” of pertussis when schools closed for the summer.

Now, with schools ready to reopen, the alert is renewed, Pinette said.

“We were hoping that when school got out it would kind of die down a little bit,” Pinette said. “We were hoping to see before school that the numbers drop, but it’s still continuing at a steady pace.”

Doug Harlow — 612-2367

dharlow@centralmaine.com