Table 2.
Analytical performance characteristics of the Xpert SA Nasal Complete Assay in which swabs were tested directly compared to broth enrichment culture for detecting MRSA colonization in nares and/or inguinal samples.
| Direct Xpert SA Nasal Complete Assay Results |
Broth Culture Results |
% (95% CI) |
||||
|---|---|---|---|---|---|---|
| MRSA + | MRSA − | Sensitivity | Specificity | PPV | NPV | |
| Naresa | ||||||
| MRSA + | 25 | 6 | 83 (66–93) | 95 (90–98) | 81 (63–91) | 96 (91–99) |
| MRSA − | 5 | 124 | ||||
| Inguinalb | ||||||
| MRSA + | 31 | 3 | 84 (64–88) | 97 (93–99) | 91 (76–98) | 94 (88–98) |
| MRSA − | 6 | 102 | ||||
| Combined Nares/Inguinalc | ||||||
| MRSA + | 39 | 3 | 89 (76–96) | 97 (90–99) | 93 (80–98) | 95 (89–99) |
| MRSA − | 5 | 95 | ||||
n = 160.
n = 142.
n = 142
If either nares or inguinal specimens were positive, then the combined result was considered positive. MRSA, Methicillin-resistant Staphylococcus aureus; CI, confidence interval; PPV, positive predictive value; NPV, negative predictive value.
There was missing data for 22 of the 162 enrolled participants; 20/22 were from inguinal samples and 2/22 from nasal samples. Reasons for these included: 12/162 patients declined inguinal swab collection, 6/162 samples generated errors on the Xpert instrument (5 increased syringe pressure, all from inguinal samples and 1 probe check failure from a nasal sample), and 4/162 samples with invalid results (3 inguinal, 1 nares).