SIOUX CITY, Iowa (AP) — Officials are blaming an outbreak of norovirus for an illness that sickened dozens of students at a Sioux City elementary school. The Sioux City Journal reports that Siouxland District Health Department announced Tuesday that lab results show the virus caused more than 40 students and three staff members at Bryant Elementary School to become ill on Thursday. Another 33 students reported being sick Friday.

Norovirus is a common food-borne pathogen with symptoms including vomiting and diarrhea. Health department Deputy Director Tyler Brock says it’s unclear where the illness originated or if it was contracted at the school.