(CNN) A school district in Colorado has closed more than 40 schools for two days after a virus outbreak rapidly spread through the student population, according to school officials.

It's the first time the Mesa County Valley School District 51 has had to close all schools due to illness, the district said Wednesday.

"We are taking this highly unusual action because this virus is extremely contagious and spreading quickly across our schools," Nursing Coordinator Tanya Marvin said in the statement.

More than a dozen schools in the state's 14th largest district reported increased absences "due to illness and several incidences of vomiting in public areas of the schools," according to the Mesa County Public Health Department

A second, related virus has also been affecting students in recent weeks, the district said . "The combination of the two has created an unprecedented spread of illness."

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