KANSAS CITY, Mo. (AP) — Missouri now has 10 cases of measles, including three students, according to health officials.

The Kansas City Health Department plans to announce seven more exposure sites in the Kansas City area soon, the Kansas City Star reported .

The three students with the virus attend Liberty Public Schools, according to Bill Snook, department spokesman. Two of the students pose no risk, but the third may have exposed others at South Valley Middle School last week.

Children who aren’t immunized are being held out of the school for a three-week period in which they could develop measles, a school district spokesman said.

Missouri parents can enroll their children in schools without the required measles-mumps-rubella vaccine under a religious or medical exemption.

Lab testing from the three students revealed that they are the same outbreak, according to Kerri Tesreau, director of the division of community and public health for the Missouri Department of Health and Senior Services.

The cases may have come from an international traveler living in Missouri, Tesreau said.

Health officials in Wisconsin, Minnesota and Iowa have warned that a Missouri traveler may have exposed their residents to the virus.

The Missouri Health Department is working with health departments in the three states and the federal Centers for Disease Control to track potential exposure sites, Tesreau said.

The department hasn’t ruled out that the source of the state’s outbreak isn’t the same as a separate outbreak in a Kansas county near the Missouri border.

There are currently 18 reported measles cases in Kansas, which originated from another traveler who infected a Johnson County daycare. That incident is the largest outbreak in Kansas since 1990.

“It does not appear to be, at this point, linked to the Kansas outbreak,” Tesreau said. “But that’s preliminary.”