More cases of suspected salmonella have been reported in the southern Colorado city of Alamosa.

Jefferson County official Jim Shires says the number reached 216 on Sunday. He says nine people have required hospital treatment.

Health officials believe the outbreak may be caused by Alamosa’s municipal water system. Residents have been told to stop drinking and cooking with tap water.

Public officials plan to begin flushing the city water system with a chlorine solution on Tuesday. The process could take several days.

The state activated the Colorado National Guard on Friday to help distribute safe water.