The Michigan Department of Community Health said the illnesses occurred in children and adults in lower Michigan. At least two people were hospitalized. Nine cases have been confirmed as influenza B viruses, two as influenza A (H3N2) virus and one as influenza A (H1N1) 2009 virus.
Officials say it's too early to tell what influenza viruses will circulate this influenza season or its severity.
The Centers for Disease Control and Prevention is expected to report Michigan's flu activity as "sporadic" — the lowest of four levels of influenza activity.