DUBUQUE, Iowa (AP) – Health officials are puzzled by an outbreak of the mumps among Dubuque County students that has now climbed to 30 cases, which is more than one-third of all cases statewide. According to Dubuque County Health Department executive director Patrice Lambert, the source of the outbreak has not yet been determined. Lambert says this is the worst outbreak in 10 years in the county.

Dubuque Community School District’ health services coordinator, Rhonda Ramler, says officials haven’t seen a pattern to the students who have been affected. The Telegraph Herald reports that precautions are being taken to try and halt the spread of the disease, which can cause fever, headaches and swollen salivary glands.