ST. CLOUD — Elevated carbon monoxide levels at a St. Cloud State sorority house sent nine people to the hospital this week.

Reports said the house had to be evacuated until the problem was fixed.

Police and firefighters were called after a doctor at St. Cloud Hospital detected elevated carbon monoxide levels in a tenant who went to the emergency room.

St. Cloud Fire Marshal Mike Post said rescuers went to the house early Wednesday and found potentially dangerous carbon monoxide levels.

Post said the fire department was called to the same house about a week earlier on a report of a gas smell but couldn’t find anything.

A clogged vent line in a water heater may have been the source. The house owner replaced the water heater Thursday.