State and city health officials are investigating after 22 students at Portland’s Reiche Elementary School suddenly came down with a stomach ailment this week.

District food services officials have sent samples of the food served at the school to a state laboratory for testing, the results of which are pending, the Portland Public Schools announced in a Friday afternoon news release.

The district stated in its release that the Maine Center for Disease Control and Prevention and city of Portland Health Division were notified because of “the unusual number of cases and presentation.”

The students each experienced upset stomachs and vomiting, but all 22 reported feeling improvements within hours and have since returned to school — 21 returned to classes the following day — the district stated.