BIRMINGHAM (AP) — At least five north Alabama school systems with about 25,000 students total are canceling classes because of the flu.

The city school systems in Albertville, Boaz and Guntersville have joined the Cullman County and Marshall County system in shutting down until next week.

State statistics show Marshall County is the largest system affected by the illness with 5,468 students in kindergarten through the 12th grade. Marshall County plans to resume classes on Tuesday; the others return on Monday.

Gov. Kay Ivey declared a flu emergency earlier this month because of an outbreak of the illness.

State Health Department officials have said they are investigating more than 50 deaths potentially linked to a flu outbreak statewide, and the agency has been special clinics to vaccinate people against the disease.