Methods: A total of 504 nasal specimens were collected in the Copan dual swab systems from patients with ages between 0 to 61 years with 91.9% patients ≤ 21 year-old(n=463). For each sample, one swab was tested with Xpert SA. The second swab was plated onto Blood agar, Mannitol salt agar and ChromID™ MRSA plate and incubated at 35°C in non-CO2 incubator. The identification of SA and MRSA was compared between Xpert SA and the culture results. Methicillin resistance was determined using conventional methods (susceptibility testing or detection of altered penicillin binding protein).
Results: When compared with culture for the identification of SA (n=481), there was an agreement of 95.0% with sensitivity and specificity being 95.6% and 94.8%, respectively. Among those culture-confirmed and Xpert SA positive samples (n=131), concordance between Xpert SA and conventional methods for detection of methicillin resistance was 97.0% with sensitivity and specificity being 100% and 96.3%, respectively. Four culture-confirmed methicillin susceptible SA (MSSA) were identified as MRSA by Xpert SA. Among 504 nasal specimens, twenty-three (4.6%) samples had invalid or instrument failure results. Nasal swabs collected from pediatric patients (≤21 year-old) had a higher invalid/instrument failure rate (5.0%) than those from adults (0%) (p<0.001).
Conclusion: Xpert SA Nasal Complete assay provides a rapid and sensitive method to detect and differentiate between MSSA and MRSA colonization. The higher invalid rate in pediatric patients and misidentification of MSSA as MRSA by Xpert SA warrant the confirmation by bacterial culture and conventional susceptibility test.
D. Salamon, None
A. Leber, Nationwide Children's Hospital: Research Contractor , Research support .