State health officials say 26 cases of whooping cough have been reported so far this year, compared with eight by March 14, 2007.

Bonnie Barnard with the Department of Public Health and Human Services says the number of cases concerns her, especially because of how contagious it is.

The bacteria has shown up mainly in western Montana, with 16 cases in Lake County and six in Flathead County. Whooping cough, or pertussis, has also been reported in Missoula, Ravalli, Cascade and Yellowstone counties.

Symptoms include a prolonged cough that ends in a whooping sound when the person takes a breath.

Health officials are asking that people be aware of the symptoms and seek preventive treatment if they've been around someone who has whooping cough.

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