ALMA, Wis. -

There are nine confirmed cases of pertussis, or whooping cough, in the Alma School District, according to the Buffalo County Public Health Department.

The health department says the disease exposure and spread began on May 6 and involves mostly Buffalo County residents, but also some people in Wabasha, Trempealeau, La Crosse and Pepin counties.

Pertussis is a contagious bacterial disease, which is spread by the coughing of an infected person. It can impact anyone, but the effects of pertussis are most severe in babies and young children, the health department said.

"We've contacted people who have possibly been exposed, and, if needed, they are being treated," Bufflao County Public Health Officer Jen Rombalski said in a statement. "Some people with symptoms have also been treated who weren’t able to get tested before the treatment. In the meantime, we’re working with our partners to inform parents about pertussis and are investigating any new exposures."

Rombalski says at first, the symptoms are similar to a cold and a mild, irritating cough for a week or two. When the illness gets worse, the child may have explosive coughing and may have trouble breathing because of it. Following the cough, you may hear a loud crowing or “whooping” sound as the child tries to inhale the air, the health department described.

According to the Wisconsin Division of Public Health, 338 pertussis cases have been investigated statewide between January 1 and June 2 of this year. During this time period last year, 3,270 cases were reported.

Click here for more information on pertussis from the Wisconsin Department of Public Health.