The emergence of decreased susceptibility to vancomycin in Staphylococcus epidermidis

BACKGROUND: Coagulase-negative staphylococci (CNS) are the major cause of n osocomial bloodstream infection. Emergence of vancomycin resistance among C NS is a serious public health concern, because CNS usually are multidrug-re sistant, and glycopeptide antibiotics, among which only vancomycin is avail able in the United States, are the only remaining effective therapy. In thi s report, we describe the first bloodstream infection in the United States associated with a Staphylococcus epidermidis strain with decreased suscepti bility to vancomycin. METHODS: We reviewed the hospital's microbiology records for all CNS strain s, reviewed the patient's medical and laboratory records, and obtained all available CNS isolates with decreased susceptibility to vancomycin. Blood c ultures were processed and CNS isolates identified by using standard method s; antimicrobial susceptibility was determined by using minimum inhibitory concentration (MIC) and disk-diffusion methods. Nares cultures were obtaine d from exposed healthcare workers (HCWs) to identify possible colonization by CNS with decreased susceptibility to vancomycin. RESULTS: The bloodstream infection by an S epidermidis strain with decrease d susceptibility to vancomycin occurred in a 49-year-old woman with carcino ma. She had two blood cultures positive for CNS; both isolates were S epide rmidis. Although susceptible to vancomycin by the disk-diffusion method (16 -17 mm), the isolates were intermediate by MIC (8-6 mu g/mL). The patient h ad received an extended course of vancomycin therapy; she died of her under lying disease. No HCW was colonized by CNS with decreased susceptibility to vancomycin. CONCLUSIONS: This is the first report in the United States of bloodstream i nfection due to S epidermidis with decreased susceptibility to vancomycin. Contact precautions likely played a role in preventing nosocomial transmiss ion of this strain, and disk-diffusion methods may be inadequate to detect CNS with decreased susceptibility to vancomycin.