CHICAGO (AP) — New research says the most common reason why many surgery patients go back to the hospital is infections around the incision.

Symptoms typically show up several days after patients go home but most infections begin in the hospital.

The study of almost 350 hospitals also found that readmission rates vary widely by surgery.

The lowest unexpected readmission rate in the study was just under 4 percent for hysterectomy patients. The highest was almost 15 percent, for artery disease patients who had surgery to reroute blood flow in the legs.

The study’s lead author says to avoid re-hospitalization and dangerous complications, patients should seek treatment at the earliest sign of an infection. That may include redness or swelling.

The study was published Tuesday in the Journal of the American Medical Association.