DURANGO, Colo. (AP) -- Federal health investigators are in La Plata County to study the county's high rate of whooping cough.

Investigators from the Centers for Disease Control and Prevention are looking for clues to explain La Plata's unusually high rate of pertussis, also called whooping cough.

Dr. Sema Mandal of the CDC says the whooping cough cases in La Plata County are unusual. In the first half of this year, La Plata accounted for more than a third of all the pertussis cases in Colorado, 55 of 146 cases.

Immunizations are being offered at the San Juan Basin Health Department. The CDC investigation should take about three weeks.

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