Health officials in several Quebec regions are concerned about an increase in whooping cough among adults.

There have been 15 new cases in the last six weeks in the Lower St. Lawrence — the area between Quebec City and the Gaspé that includes Rimouski and Rivière-du-Loup — and 30 in the Mauricie, north and northeast of Montreal.

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A vaccine protects against whooping cough, but young children sometimes don't get all five doses and too many pre-teens skip the booster shot. (Associated Press)

The disease is extremely contagious, said Claude Gauthier, an infectious disease specialist with the Lower St. Lawrence public health agency, but not very dangerous. Infants and children are at most risk, but are typically immunized against it.

The problem, Gauthier said, is that adults who contract it don't go to see a doctor soon enough and so continue to spread the bacteria through their coughs.

"Adults are susceptible to whooping cough. But people seek care too late, and once we're aware of it, they're no longer contagious," Gauthier said.

He said the period of contagiousness lasts two to three weeks, while sometimes violent coughing can endure for another three weeks after that.

9 deaths in U.S.

Whooping cough, also known as pertussis, is caused by bacteria from the genus bordetella and spread by coughing and sneezing. It feels like a cold at first and is followed by weeks of dry coughing but no fever.

There's been a resurgence of the disease in areas of Canada and the United States, health officials say.

As of last Tuesday, there were 1,155 confirmed cases of pertussis in New Brunswick, which the Public Health Agency of Canada says is experiencing an outbreak.

Public Health Ontario reported 170 cases between January and the end of April, a rise from 29 cases during the same period last year. The region around Lethbridge, Alta., has seen more than 40 cases so far this year, up from its annual average of one to three.

An outbreak in the United States earlier this year infected 18,000 people and caused nine infant deaths. The outbreak raised concerns that the new standard vaccine introduced in 1997 might wear off sooner than its predecessor and earlier than expected.

Immunizing young children against the disease requires five shots, then a booster at 11 to 12 years of age. One problem is that not all children get all five doses, and only about two-thirds get the booster injection.