Resistant staph microbe reappears.

Doctors in the United States recently identified three cases of staph infection that resist vancomycin, the only antibiotic thought still to be effective against such stubborn infections.

In 1996, a Japanese infant became the first to contract a Staphylococcus aureus infection that resisted vancomycin. The boy was cured with a combination of other drugs. Now, two studies in the Feb. 18 New England Journal of Medicine describe three more cases--in Michigan, New Jersey, and New York.

All three had received kidney dialysis and died from kidney failure or a combination of ills. Although the staph infection's role in the deaths was unclear, these cases indicate that any dialysis patient with an S. aureus infection who doesn't promptly respond to vancomycin should be tested for resistance, says Michele L. Pearson, an epidemiologist at the Centers for Disease Control and Prevention in Atlanta.

Of 222 people known to have come into contact with any of the three patients, none contracted the resistant strain.

The patients had received vancomycin intermittently for about 4 months. Such repeated exposure to antibiotics can induce resistance. The cases represent another warning against doctors overprescribing antibiotics, says Pearson, a coauthor of one of the new studies.