State health officials are investigating an apparent E. coli outbreak that has sickened 13 Minnesotans and sent four to the hospital.

Seven of the patients reported eating at Applebee's restaurants in Woodbury, Roseville, Blaine, Monticello and Duluth between June 24 and June 27, the Minnesota Department of Health said Monday. But there are also several cases with no apparent connection to the restaurant chain, indictating the illnesses may have resulted from a widely distributed food product.

The four hospitalized patients — all of whom reported eating at Applebee's — were treated mostly for dehydration and have now been discharged, according to Stephanie Meyer, a Health Department epidemiologist. All 13 patients, ranging from ages 16 to 84, have recovered or are recovering.

E. coli is a bacterial infection that can cause stomach cramps and severe diarrhea. Most patients recover within five to 10 days, but the disease can cause serious complications, particularly in the elderly, young children and people with weakened immune systems.

According to health officials, this form of E. coli 0111 is in the same family as the more well-known E. coli 0157:H7.

About 10 outbreaks of E. coli are reported in Minnesota every year, Meyer said, and the state usually sees about 20 to 30 cases of E. coli 0111 total each year.

"To see 13 all at once is unusual," Meyer said. "We don't know what that means yet."

Several of the patients reported eating Applebee's Oriental Chicken Salad, which contains cabbage, shredded carrots, crispy noodles, almonds and fried chicken. Applebee's is cooperating with the investigation, Meyer said, and has voluntarily pulled the dish from its menu and removed cabbage and shredded carrots from other items.

None of the ingredients were exclusive to Applebee's, the restaurant said in a statement Monday. There are no indications of E. coli risk at Applebee's restaurants outside Minnesota, and all locations outside the state will continue with unmodified menu items.

"The fact that we have multiple Applebee's locations indicates that it was food that could have gone to restaurants and elsewhere," Meyer said. The state Department of Agriculture and other regulatory partners are tracing invoices to produce suppliers in an attempt to find any commonalities.

Cross-referencing produce shipments with other customers and other E. coli reports can help investigators pinpoint the source of the bacteria, Meyer said. "There could be a large network involved."

The investigation could take as little as a week up to a few months, depending on how complex the supply chain is, said Carrie Rigdon, supervisor of the Department of Agriculture Rapid Response Team.

There is often a delay between the time a patient notices symptoms and the time the infection is diagnosed and reported to the Health Department, Meyer said, so many more cases could still emerge.

"We hope not, but there's always a possibility," she said.

While investigators try to determine the source of the outbreak, anyone who has eaten at an Applebee's and experienced E. coli symptoms is asked to contact the state Health Department.

Samantha Schmidt • 612-673-4641