No abstract

The use of an assay with rapid results reduced the use of antistaphylococcal therapy among patients who did not have S. aureus bacteremia; it also decreased the use of MRS drug therapy and led to earlier appropriate therapy among patients with MSSA bacteremia.

The use of an assay with rapid results reduced the use of antistaphylococcal therapy among patients who did not have S. aureus bacteremia; it also decreased the use of MRS drug therapy and led to earlier appropriate therapy among patients with MSSA bacteremia.

Letters to the Editor Identification of Methicillin-Resistant or Methicillin-Susceptible Staphylococcus aureus in Blood Cultures and Wound Swabs by GeneXpert ᰔ Until a decade ago, clinicians could use epidemiological clues to select empirical therapy for methicillin-susceptible Staphylococcus aureus (MSSA) or methicillin-resistant S. aureus (MRSA) (5). The emergence of MRSA as a community pathogen and the documentation of the inferiority of nonbeta-lactam antibiotics in treating MSSA bacteremia greatly complicate initial antibiotic choice (2-4, 7, 8, 9). Early identification and determination of antibiotic susceptibility might help focus initial antibiotic therapy. We compared a multiplex PCR that identifies MSSA and MRSA to standard microbiologic techniques for evaluating the results of blood cultures (BCs) and wound swab (WS) cultures. Blood was cultured in BacT/Alert, and drug susceptibility was determined with a Vitek 2 system (both from BioMerieux, Durham, NC). For BCs judged to contain gram-positive cocci in clusters (GPCCl), 1-ml aliquots were centrifuged (2 min at 3,000 rpm) to remove charcoal, and the supernatant was studied in a GeneXpert system (Cepheid, Sunnyvale, CA). WS samples were streaked to standard media (blood, chocolate, McConkey, and colistin-nalidixic acid) and then studied in the GeneXpert system within 48 h of collection. GeneXpert realtime PCR detects proprietary sequences of the S. aureus protein A gene, the staphylococcal cassette chromosome, and the methicillin resistance element (1). Of 223 blood samples, 68 yielded S. aureus by culture, 47 with MRSA and 21 with MSSA. PCR correctly identified 67/68 (98.5%) S. aureus isolates (Tables 1 and 2), including 46/47 (97.9%) MRSA and 21/21 (100%) MSSA isolates. No BC (155/155; 100%) that contained GPCCl without S. aureus contained S. aureus by PCR. Of 321 WS samples, 106 yielded MRSA and 51 MSSA by culture. PCR identified 104/106 (98.1%) MRSA isolates correctly but misidentified 2 MRSA isolates as MSSA (Table 1). Of 51 MSSA isolates, 47 (92.2%) were identified correctly, 3 incorrectly as MRSA, and 1 incorrectly as no S. aureus by PCR.

Despite widespread pneumococcal vaccination of children and adults, invasive pneumococcal disease (IPD) remains prominent. Using our database of all Streptococcus pneumoniae infections at the Veterans Affairs Medical Center, Houston, Texas, since 2000, we reviewed cases of IPD, defined as the isolation of pneumococci from any normally sterile body site. In 136 cases, the mean age of patients was 63 years; 43% were African American, a higher proportion than the 30% served by our hospital. One hundred sixteen patients (85%) had pneumonia, of whom 3 also had empyema. Seven had bacteremia with no apparent source, 5 meningitis, 5 spontaneous bacterial peritonitis, 3 septic arthritis, 2 endocarditis, and individual patients had osteomyelitis and/or localized abscesses. One hundred twenty-one patients (89%) had > or =1 underlying condition associated with susceptibility to pneumococcal infection, and another 8 (6%) were aged >65 years old. Thus only 5% of patients lacked a condition for which 23-valent pneumococcal polysaccharide vaccine (PPV23) is recommended. Fifty-five percent had been vaccinated; similar proportions of vaccine serotypes infected previously vaccinated and nonvaccinated patients. All but 2 isolates were fully susceptible to penicillin and cefotaxime as currently defined. Consistent with substantial replacement of infecting serotypes since the introduction of 7-valent pneumococcal conjugate vaccine (PCV7), none of the predominant infecting serotypes was included in PCV7, although all except for 6A were contained in PPV23. The overall mortality at 30 days was 16% and was similar in vaccinated and nonvaccinated subjects. IPD causes a wide spectrum of disease. Mortality is substantial. PPV23 is clearly not fully protective.