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"This was 40 per cent of the provincial total from that time period," Dr. Ninh Tran, medical officer of health for Southwestern Public Health, said in an interview.

"It's a significant increase ... that is certainly striking."

Previous years have seen annual caseloads in the single digits, Tran said.

Whooping cough, or pertussis, can see a person's cough intensify to the point where a "whooping" sound is heard when they try to catch their breath, Tran said.

Lower rates of immunization against whooping cough could be a factor in the rise in cases, he said.

"In our region, we have relatively lower rates of immunization compared to others," Tran said.

"We've had a few cases that were hospitalized. That's why we just really need folks to get up-to-date on their immunization."

Huron Perth Public Health, which serves Stratford, Wingham, Listowel and Clinton, said it has confirmed at least 21 cases of whooping cough so far this year. In 2022, there were only three cases.

"The illness can be serious for infants younger than 12 months of age who are not vaccinated, or who have not received all doses of the pertussis vaccine," Dr. Miriam Klassen, the medical officer of health for Huron Perth, wrote in a statement.

"Young children have the highest risk for severe complications, such as hospitalization and death, if they get sick."

Klassen said the COVID-19 pandemic might have put residents of southern Ontario behind on routine immunizations, and urged residents to catch up on their vaccines.

The Windsor-Essex County Health Unit said there had been "a recent dramatic rise" in whooping cough cases in its region. It said last week that it counted 18 cases since November 2022.

"Cases have predominately been clustered in the Leamington and Kingsville communities, and exclusively in children who are unvaccinated or partially vaccinated," it wrote in a statement, urging residents to get vaccinated.

The health unit noted that the cough brought on by pertussis can be so severe that it can cause vomiting. If left untreated in infants, young children and the elderly, it "can lead to complications such as pneumonia, dehydration, brain damage, hospitalization and death."

Wellington-Dufferin-Guelph Public Health said it recorded 12 cases over the fall and winter, which is "higher than normal for the region."

"Many individuals may be behind in their vaccinations because they were unable to get them due to COVID-19," it wrote in a statement. "Now is the time to get fully vaccinated as we engage in more community activities."

This report by ºÃÉ«tvwas first published March 27, 2023.