My 11-year-old daughter has had two positive C. difficile stool tests in the past three weeks. After an initial test (following bowel problems and bloody stools), she was given an antibiotic to treat this bacterium. However, the doctor and I are puzzled as to the cause of this infection, because it is usually due to the overuse of antibiotics, and that is not the case with my daughter. We cannot determine the cause, and she has not been receptive to treatment. Any comments?

C.O.

Clostridium difficile is a bacterium that causes diarrhea by secreting toxins (poisons) that attack the lining of the gut. The symptoms of C. difficile infection vary from a mild watery diarrhea to severe inflammation and enlargement of the colon and even death.

C. difficile colonizes the gut only after the normal flora (harmless microorganisms) of the colon have been altered, usually by taking antibiotics. This process occurs quite commonly in hospitalized patients taking a long course of antibiotics. The normal bacteria in the colon are eradicated, somehow allowing C. difficile to multiply and release toxins. To make the diagnosis of C. difficile disease, a physician must detect these toxins in the stool. It is not enough to detect the bacteria without the toxins, because not all strains of C. difficile make the toxins and cause the disease.

Let us assume that your daughter has been correctly diagnosed with C. difficile colitis, meaning that toxin was detected in her stool. How did she get this infection? You say that she has not overused antibiotics, but I wonder if she has taken any at all. I have seen several cases of this disease when the patient took only one dose of an antibiotic 10 days or so before the diarrhea started. There are also countless reports of people developing C. difficile disease after taking drugs that are not considered antibiotics but that have some effect on bacteria, mainly anti-cancer treatments.

Even if your daughter has not taken any antibiotic, or any drug for that matter, she could still have C. difficile disease. There have been many reports describing cases like this. Many of these patients worked in the health-care setting and presumably acquired the organism there. There were no obvious explanations for why C. difficile caused disease in these patients.

Treating C. difficile diarrhea is relatively straightforward. First, the antibiotic that caused the problem should be discontinued if possible. In the United States, there are two drugs that can then be used to treat the C. difficile infection itself: vancomycin (trade name Vancocin) and metronidazole (Flagyl). Because vancomycin is expensive and because taking it can lead to the growth of vancomycin-resistant bacteria, metronidazole is usually the drug of choice. If a patient is very ill, we often give vancomycin orally and metronidazole intravenously.

About 10 percent of patients have a relapse of C. difficile diarrhea. Relapses are not due to antibiotic resistance to the treatment, so another course of metronidazole is often successful. If not, a long tapering course of vancomycin usually works. It may also help to prevent relapses if patients reestablish the normal colon flora by ingesting special capsules that contain bacteria or yeast.