The department says the illnesses occurred in children and adults from two southeast Michigan counties. Three of the cases have been confirmed as influenza A (H1N1) 2009 viruses and one has been confirmed as being an influenza A (H3N2) virus.
The department is urging people to get flu shots. Officials say it's too early to tell what influenza viruses will circulate or how severe the influenza season may be. Michigan's flu activity is to be reported by the federal Centers for Disease Control and Prevention as "sporadic."
Officials with the MDCH say the flu season is hitting the state earlier than usual.
To help protect against contracting the flu, the CDC recommends covering your mouth and nose when sneezing, wash hands thoroughly with soap and warm water and avoid touching your hands to your mouth and eyes.