The public health community has been sounding the alarm for years about the overuse of antibiotics and the emergence of “superbugs”  bacteria that have developed immunity to a wide number of antibiotics. But the C. difficile problem shows that the threat is not generalized or hypothetical, but immediate and personal.

“One of the things that we counsel consumers about is to make sure that an antibiotic is really necessary,” said Dr. Dale N. Gerding, an infectious disease specialist at the Stritch School of Medicine at Loyola University in Chicago. “There are many good reasons for taking an antibiotic, but an illness like sinusitis or bronchitis winds up being treated with antibiotics even though it will go away by itself anyway.”

Even appropriate use of antibiotics can put a person at risk. Dr. Gerding said his own adult son came down with a C. difficile infection after taking antibiotics for tonsillitis.

The typical treatment for C. difficile is another course of antibiotics, typically the drug vancomycin. But the situation can quickly turn tragic. The Centers for Disease Control and Prevention has reported on several cases of pregnant and postpartum women who developed life-threatening C. difficile infections after being treated for minor infections. In some instances, a C. difficile infection can be treated only by emergency surgery to remove the patient’s colon. Doctors say many patients report that they continue to suffer from regular bouts of diarrhea even after the infection is gone. About 20 percent of patients with the infection suffer a relapse, and C. difficile support groups have emerged on the Internet.

In the case of the Mitchell family, Mr. Mitchell had been taking antibiotics for another health problem, and the treatment apparently led to his C. difficile infection. Mrs. Mitchell probably contracted the illness from her husband. The spores from C. difficile are hardy, and contaminated surfaces must be scrubbed down with bleach to eradicate the germ. Doctors say Mrs. Mitchell’s illness is unusual because most people are protected by their own bacterial flora and wouldn’t be vulnerable to C. difficile if they had not been taking antibiotics, even after close exposure. The risk of contracting C. difficile outside the health care setting remains low, at about 7 cases per 100,000 people, studies show.