A common virus may be the cause of many hard-to-treat cases of inflammatory bowel disease, researchers in Italy report.

More than one third of patients in a new study who had colitis that did not respond to steroids were infected with cytomegalovirus (CMV), the investigators found.

A form of inflammatory bowel disease, ulcerative colitis causes the large intestine to become inflamed and ulcerated, leading to bloody diarrhea, abdominal cramps and fever. Colitis can also occur in patients with Crohn's disease, a chronic inflammation of the intestinal wall.

More than half of the population is infected with CMV, a type of herpesvirus. The virus rarely causes problems in adults with healthy immune systems, although it can cause symptoms in people with weakened immune systems, such as those infected with HIV -- the virus that causes AIDS.

Previous reports have linked CMV infection to relapses of inflammatory bowel disease, especially in cases that are resistant to steroids used to treat the illness. But the rate of CMV infection among patients with inflammatory bowel disease is uncertain.

To see how common CMV infection is among patients with inflammatory bowel disease, researchers studied 55 patients with ulcerative colitis and seven with Crohn's disease. In 30% of the patients, steroid therapy did not clear up symptoms.

To test for CMV infection, the researchers performed rectal biopsies in the patients whose symptoms were resistant to steroids.

CMV was present in 36% of patients.

The American Journal of Gastroenterology March 2001; 96: 773-775