Symptoms of whooping cough usually start five to 21 days after someone has been exposed. ((iStock))

New Brunswick health officials are encouraging people to get immunized against pertussis, also known as whooping cough.

The highly contagious bacterial infection has now been confirmed at two schools in the province – Forest Hills Elementary School in Saint John and Riverview Middle School in Moncton.

And the province is overdue for an outbreak, said Dr. Yves Leger, the regional medical officer of health for the Moncton area.

A "wave" of whooping cough usually occurs every three to five years and the last one to hit New Brunswick was in 2004, he said.

Immunization can help prevent a spike in the infection, said Leger.

"It's really important for kids to be up to date with their immunization and for the adolescents who are in schools, when we offer that dose, it's important for them to get it so that they can keep their protection really high," said Leger.

"And for adults as well to get their dose either when they're getting their booster shot of tetanus."

Whooping cough can affect people of any age, but is most severe among young infants.

'Adults that were vaccinated when they were young, if they haven't received a dose since then, they more than likely don't have any leftover protection.'—Dr. Yves Leger, Moncton regional medical officer of health

Many adults develop the infection and pass it along to children, said Leger.

"Adults that were vaccinated when they were young, if they haven't received a dose since then, they more than likely don't have any leftover protection," he said.

A child under six years needs five doses of the pertussis vaccine, starting at two months of age, to be fully immunized. An additional booster dose, combined with tetanus and diphtheria (Tdap) vaccine, is given routinely to adolescents between 14 to 16 years of age across Canada.

It is recommended that adults not previously immunized against pertussis receive one dose of the Tdap vaccine.

Whooping cough is an infection in the respiratory tract that resembles a common cold except for the prolonged coughing.

Symptoms include sneezing, runny nose, low grade fever and coughing that often ends with a whooping sound before the next breath.

Earlier this week, one case of whooping cough was confirmed at Forest Hills Elementary School in Saint John.

Three more cases have since been found at Riverview Middle School in Moncton.

The schools have notified parents.

"It's really in the hopes of finding other cases quickly, having them assessed and treated quickly so that we can slow down the spread of the infection," said Leger. "Pertussis is very transmissible and very infectious."

Whooping cough is spread through droplets in the air from an infected person’s coughs or sneezes. It can also be spread through coming in contact with discharges from an infected person’s nose or throat.

Symptoms usually start five to 21 days after someone has been exposed. Patients are most contagious during the first two weeks, but may last up to three weeks.

One to three deaths from whooping cough occur each year in Canada, particularly in infants too young to have begun their immunization and infants who have not received all of the doses required to be fully immunized.