A public health unit in central Ontario is the latest to warn about rising cases of pertussis — or whooping cough.

The Haliburton, Kawartha Pine Ridge District Health Unit issued an alert earlier this week about increased whooping cough activity within the school community. The health unit serves Kawartha Lakes, Northumberland and Haliburton counties.

Marianne Rock, HKPR’s communicable disease and prevention control, advises monitoring children for symptoms including a runny nose and mild fever. However, severe coughing and the distinctive “whoop” sound begins within a few days.

“We’re finding that there are a number of children who are sick with pertussis symptoms,” she said.

The highest at-risk group are infants under the age of one and pregnant individuals in their third trimester, the health unit says. If exposed or symptomatic, individuals should contact their health care provider immediately for further assessment.

According to Ontario Public Health, between January and May of 2024, there were 70 whooping cough cases reported across the province.

Cases have steadily climbed the past three years — from 16 reported in 2021 to 159 in 2022 and 333 in 2023.

Some epidemiologists attribute the spike in cases due to lagging childhood immunization, in part due to the closure of clinics during the onset of the COVID-19 pandemic in 2020.

“COVID was a big disrupting factor for a lot of people for a lot of different reasons,” said Dr. Christopher Labos, a cardiologist with a degree in epidemiology at McGill University.

“But most important, a lot of parents of young children missed regular follow-up appointments.”

Labos said the most effective defence against pertussis is immunization.

“We don’t want to see preventable diseases going up,” he said. “We want to see them under control and one of the best ways to do that is make sure our vaccination rates stay high.”

But some experts note the lack of immunization could also be attributed to misinformation distributed about vaccines.

“It was related to COVID vaccination,” said Zahid Buttt, an infectious disease epidemiologist and an assistant professor at the University of Waterloo.

“There were a lot of conspiracy theories and that kind of increased vaccine hesitancy overall as well.”

Butt notes while the disease hasn’t impacted hospital care, whooping cough is highly transmissible.

“If you are infected, that means you can affect 15 to 17 persons who are susceptible to a particular disease,” he said. “That’s how contagious this disease is.”

Adults should also review their immunization status and get a booster dose if necessary.

“Immunity from this vaccine wanes over time, so it’s always good to get a booster dose,” Butt said.

— with files from Germain Ma/Global News Peterborough