COLUMBUS, Ohio -- Dog- or cat-owners who have suppressed immune systems may be at risk of catching a serious gastrointestinal infection from their pets, an Ohio State University expert says.

Researchers reviewed the cases of 13 immune-suppressed patients who suffered from peritonitis caused by the bacterium Pasteurella multocida. They found that nearly 70 percent of the patients owned or had contact with a household pet.

Peritonitis is a painful inflammation of the peritoneum, the membrane that lines the wall of the abdomen. P. multocida is a bacterium commonly found in the nose and throat of healthy domestic animals; scientists estimate that two-thirds of all dogs and 90 percent of all cats carry it.

The researchers suspect that the patients who were reviewed in the study inhaled P. multocida bacteria, which then spread to the bloodstream and ultimately to the peritoneum.

"Pets could play an important role in the development of

spontaneous bacterial peritonitis in people who are immune- compromised," said Christian A. Koch, a clinical instructor in internal medicine at Ohio State and lead author of the review article.

"Patients should be informed of the potential infectious risk of household pet exposure and may even be advised to minimize animal contact, particularly with cats and dogs."

Koch's co-authors on the review article are Christopher L. Mabee and Jamie A. Robyn, clinical instructors in internal medicine; Susan L. Koletar, an associate professor of internal medicine; and Earl N. Metz, professor of internal medicine, all from Ohio State. The group's work was published in a recent issue of The American Journal of Gastroenterology.

The researchers decided to review the documented cases of P. multocida peritonitis among immune-compromised patients after treating a 66-year-old patient with spontaneous bacterial peritonitis. The patient had cirrhosis of the liver and squamous cell cancer of the head and neck -- both conditions resulting in immune system suppression -- and reported owning a cat.

"When we found that the bacterium causing the peritonitis was P. multocida, we couldn't really explain why that would be the case," said Koch. "It's a very unusual bacterium for peritonitis. When we tried to trace where it might have come from, that led us to domestic animals."

Koch recommends that immune-compromised people -- including transplant recipients and those with AIDS -- take these findings seriously. Spontaneous bacterial peritonitis has an overall mortality rate of 30 to 40 percent; in fact, 7 of the 13 patients reviewed in the study died of complications of peritonitis. "Preventive strategies for immune-compromised patients should include minimization of animal exposure, especially with cats," he said.

At the same time, however, Koch emphasizes that the findings of this review do not prove a definitive link between household pets, immune suppression and spontaneous bacterial peritonitis.

"The available data do not enable us to make final conclusions about whether living with domestic cats or dogs represents a significant risk factor for development of spontaneous P. multocida peritonitis in immune-compromised patients," he said. Only prospective studies -- in which the disease rates of immune- suppressed pet owners and non-pet-owners are compared over time -- will do that.

In the meantime, he said, immune-compromised pet-owners should learn about the risks and make decisions about their pets on an individual basis.

"If a patient wants to live with the cat because it's his best friend, that may be the best choice," he said. "Especially with people toward the end of their lives, we want to minimize suffering. What will create greater suffering -- removing a cat or getting infections secondary to the cat? For each patient, there will be a slightly different answer."

Contact: Christian A. Koch, (614) 293-4919

Written by Kelly McConaghy Kershner, (614) 292-8308;

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