The Springfield School was closed Friday after 30 elementary students were taken to the Springfield Mayo Hospital Thursday morning with what had been thought to be carbon monoxide poisoning.
All of the students have since been released from the hospital, and hospital spokesperson Kevin Burns says that emergency operation plans were used in response to the incident.
First responders tested for carbon monoxide at the school, but the tests have turned out negative, and no gas leak has been found.
The ill students had been practicing for a choir concert at the time, and the Minnesota Department of Health is now saying that it was possibly a “Mass Psychogenic Illness” that caused them to get sick. That means that once one child began to vomit the symptoms spread quickly through the rest of the group because they believed there was some outside factor causing it.
The investigation continues.
The school has reportedly been cleared for students to return on Monday.