The whooping cough outbreak in southern Alberta continues to grow, with 92 cases now confirmed, according to Alberta Health Services.

AHS declared on June 5 that the southwestern areas of Fort Macleod, County of Lethbridge and Coaldale are the most affected. 

Three days later, AHS reported 12 confirmed cases of the illness. That jumped to 38 a week later and, as of last week, it had grown to 58 cases.

Medical officer of health Dr. Karin Goodison said the increase is to be expected given the low level of immunization against whooping cough, also known as pertussis.

"So when we see pertussis circulating in an unimmunized population, we expect a large number of cases because it's spread very easily," she said.

Goodison hopes the summer  school break will help curb the spread of the disease.

"School is a great place to share bacteria, so we may see actually a drop in the number of cases over the next while," she said.

There's also a cluster of pertussis cases in Medicine Hat, but those aren't connected to the same outbreak.

No deaths of been reported in relation to the outbreak.

There have been 266 cases of whooping cough in Alberta so far this year, according to AHS, the majority of them in the south and central health zones.

With files from Sarah Lawrynuik