Denton schools will re-open Thursday, after the Centers for Disease Control and Prevention issued new guidelines for school closures effective noon Tuesday.

Previous CDC recommendations were based on outcomes early in the outbreak that killed many children and young adults in Mexico, who became infected and succumbed to a rapidly progressive pneumonia.

Two schools in Northwest ISD, and all schools in the Denton, Lake Dallas and Ponder districts closed this week after reporting clusters of suspect cases. Two charter schools, The Education Charter District of Little Elm, and the Winfree Charter District also closed.

Local health officials were concerned that the outbreak would have similar outcomes in the U.S., but so far, the flu has not been as virulent, Dr. Bing Burton told the county commissioners Tuesday morning.

Health department spokeswoman Betsy Haggard said in an e-mail that the county health department would continue to provide guidance to area school districts as needed, but would leave the decision whether to re-open up to school officials.

The CDC now recommends that schools close only when absenteeism affects a school’s ability to function and that previously closed schools could re-open.

Although the official number of confirmed cases has not budged since last week, Denton County’s count of probable cases of swine flu continues to rise.

With only one case confirmed, the county health department counted four additional probable cases between Monday and Tuesday afternoon, bringing the total to 13. The four additional cases were reported in Carrollton, Flower Mound, Frisco and Lewisville.

Dr. Bing Burton, director of the county health department told county commissioners Tuesday morning that health officials are monitoring “multiple clusters of suspect cases” and provided commissioners with maps.

Most of the cases are in the southern part of the county, he said, but the outbreak appears to be migrating north, a similar pattern to seasonal flu outbreaks.