WELD COUNTY, Colo. (CBS4) – Health officials in Weld County say they’ve seen an increase in the number of cases of pertussis, commonly known as whooping cough, this year.

County officials said they’ve encountered the same number of cases through early October that they saw throughout 2013.

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Weld County health officials have diagnosed 116 diagnosed cases of pertussis this year. Students at seven Windsor area schools are infected. The health department notified administrators at each affected school.

“Take this seriously. It is a cough, but it is a horrible cough. It will last for months. It can cause vomiting, incredible discomfort,” Eric Aakko with the county’s health department said.

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Pertussis affects the respiratory system, causing stubborn and persistent coughing. It is very contagious and can be fatal.

The best protection against pertussis is vaccination, although it does not provide life-long immunization.

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Health officials said that for every diagnosed case of whooping cough, there are nine or 10 that are not diagnosed.