The emergence of decreased susceptibility to vancomycin in Staphylococcus epidermidis.

BACKGROUND: Coagulase-negative staphylococci (CNS) are the major cause of nosocomial bloodstream infection. Emergence of vancomycin resistance among CNS is a serious public health concern, because CNS usually are multidrug-resistant, and glycopeptide antibiotics, among which only vancomycin is available in the United States, are the only remaining effective therapy. In this report, we describe the first bloodstream infection in the United States associated with a Staphylococcus epidermidis strain with decreased susceptibility to vancomycin. METHODS: We reviewed the hospital's microbiology records for all CNS strains, reviewed the patient's medical and laboratory records, and obtained all available CNS isolates with decreased susceptibility to vancomycin. Blood cultures were processed and CNS isolates identified by using standard methods; antimicrobial susceptibility was determined by using minimum inhibitory concentration (MIC) and disk-diffusion methods. Nares cultures were obtained 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 decreased susceptibility to vancomycin occurred in a 49-year-old woman with carcinoma. She had two blood cultures positive for CNS; both isolates were S. epidermidis. Although susceptible to vancomycin by the disk-diffusion method (16-17 mm), the isolates were intermediate by MIC (8-6 microg/mL). The patient had received an extended course of vancomycin therapy; she died of her underlying disease. No HCW was colonized by CNS with decreased susceptibility to vancomycin. CONCLUSIONS: This is the first report in the United States of bloodstream infection due to S. epidermidis with decreased susceptibility to vancomycin. Contact precautions likely played a role in preventing nosocomial transmission of this strain, and disk-diffusion methods may be inadequate to detect CNS with decreased susceptibility to vancomycin.

Comparative evaluation of PathoDx Strep A test and culture for the detection of group A streptococci in pharyngeal specimens.

The PathoDx Strep A kit, a 10-min acid extraction and latex agglutination test, was compared with routine culture for the direct detection of group A beta-hemolytic streptococci (BHS) in 414 pharyngeal specimens collected from children with pharyngitis. The results showed that the latex test compared favorably with culture for detecting group A BHS in pharyngeal specimens (sensitivity 96.7%, specificity 97.9%, and positive and negative predictive values of 97.2% and 97.4%, respectively). The comparable number of false-positive (five) and false-negative (six) latex tests along with review of patient histories suggest that these discrepant results were attributable to sampling error during specimen procurement rather than deficiencies in the latex kit. In addition, clear-cut, agglutination reactions were obtained in over 96% of positive latex tests regardless of the amount of group A BHS that was recovered by culture. The PathoDx Strep A test is a rapid, reliable noncultural alternative for the detection of group A BHS in pharyngeal specimens.