Health authorities added a sixth state, Michigan, impacted by the E. coli outbreak linked to clover sprouts used in sandwiches sold by Jimmy John's restaurants, according to the Michigan Department of Community Health.

Since Feb. 6, investigators reported 19 illnesses across six states associated with eating at the sandwich shop. Two cases in Michigan required hospitalization, but authorities reported no deaths.

Investigators linked the E. coli outbreak to uncooked sprouts typically used as garnishes on sandwiches and in salads. Sprouts are frequently eaten raw and have been implicated in outbreaks of foodborne illnesses such as salmonella and E. coli in the past.

Alfalfa sprouts sold at Jimmy John's caused 140 people to fall ill to salmonella last year, according to The Christian Science Monitor. The chain said it switched to clover sprouts after the outbreak because the alternative sprouts are easier to clean.

E. coli symptoms include diarrhea, which can be bloody, and abdominal cramps with little or no fever, according to the Centers for Disease Control and Prevention. Symptoms generally last a week but can be more serious in children and the elderly.

The Food and Drug Administration requires warnings on sprout packages sold in grocery stores advising against eating them raw. The FDA does not require that warning be posted by restaurants selling raw sprouts.

Cooking sprouts kills E. coli and salmonella bacteria.

Sprouts are grown in warm, humid conditions that are ideal for bacteria growth. Contamination from animal manure or poor hygienic practices during transit can cause outbreak easily, according to the Michigan Department of Community Health.