Additional cases of a rare intestinal problem in infants continue to be reported to federal officials since the Centers for Disease Control and Prevention (CDC) halted the use of a vaccine against a common diarrheal illness earlier this month.

Rotavirus is the leading cause of diarrheal illness in children. It accounts for 500,000 visits a year to doctor's offices, most of them during the winter months. For one in every seven children who get the disease, the viral infection is severe enough to send them to a hospital, clinic or emergency room. In an era of reduced hospital stays, 50,000 youngsters in the United States are hospitalized with rotavirus each year for an average of three days and about 20 children a year die from it, according to the CDC.

RotaShield, a vaccine against rotavirus, was approved on Aug. 31 last year by the Food and Drug Administration (FDA). The vaccine is made by Wyeth-Lederle and can be administered to infants as young as 6 weeks of age, but the Advisory Committee on Immunization Practices, a consortium of private and governmental experts on infectious diseases, called for children to be immunized at 2, 4 and 6 months of age.

On July 16, the CDC halted vaccinations of children after a surveillance system run by the CDC and the FDA linked use of the vaccine to a rare bowel obstruction. Called intussusception, the condition occurs when one segment of the bowel becomes enfolded within another. All the infants afflicted have recovered, although some required surgery.

About 51 infants out of every 100,000 develop the bowel obstruction annually, according to the CDC. "By chance alone, we should have about 16 to 19 cases within one week," said Melinda Wharton, chief of the vaccine-preventable diseases branch at the CDC. As of last week, Wharton said, 25 cases had occurred within three to seven days after children were vaccinated.

While federal officials don't know if any of the cases are directly linked to the vaccine, the slight increase and the occurrences within a week of the vaccination prompted further investigation, Wharton said. Officials also moved quickly to investigate the problem because summer provides a natural lull in the rotavirus season. The hope is to complete the investigation well before winter, when rotavirus season goes into full swing.

As of June 1, an estimated 1.8 million doses of the vaccine had been distributed, according to CDC officials, who said they based that estimate on data from the manufacturer. No one knows exactly how many children have been vaccinated.

Pediatricians said bowel obstructions linked to the vaccine seem to have generally occurred within three weeks of the vaccination. "If a child received the vaccine a month or six months ago, parents don't have to worry," said Larry Pickering, head of the Center for Pediatric Research in Norfolk and editor of the Academy of Pediatrics' Red Book on immunizations practices, the academy's official guidelines for the care of children. "That's somewhat reassuring."

Symptoms of the bowel obstruction include persistent vomiting, bloody stools, black stools and abdominal distention with or without severe colic.

"Our recommendation is not to use the vaccine until we can get enough data to assure us that it is safe," said Jon Abramson, chairman of the American Academy of Pediatrics Committee on Infectious Diseases. "This is a temporary suspension. We think we will have more data in two to three months."

Information on reporting suspected cases of intussuception to the Vaccine Adverse Event Reporting System can be requested 24 hours a day by phone at 1-800-822-7967 or on the Web at http://www.nip.gov/nop/vaers.htm.