Evaluation of the BD Max MRSA XT assay for use with different swab types

Abstract

We evaluated the performance of the BD Max MRSA XT assay for use with different swab types. The 90% detection rates (95% confidence intervals) were 387 (97 to 1,551), 877 (238 to 3,230), 986 (183 to 5,287), 1,292 (328 to 5,078), 2,400 (426 to 13,518), and 5,848 (622 to 55,021) CFU/swab for Liquid Stuart, Liquid Amies, dry, Amies Gel without charcoal, ESwab collection, and Amies gel with charcoal swabs (Becton Dickinson), respectively. Amies Gel without charcoal, ESwab collection, and Amies gel with charcoal swabs had a tendency to be less sensitive, but none of the differences was statistically significant.

FIG 1

(A) Two-parameter log-logistic model-based curves for the frequency of positive MRSA results in dependency of the bacterial input per swab calculated for six different swab types. Shown are the limits of detection for 95% detection rate. The 90% detection level is also indicated. (B) Estimates for the LoD for the 90% detection rate and 95% confidence intervals for the various swabs. (C and D) Real-time PCR C_T values for serial dilutions of MRSA and detection of mecA or mecC and SCCmec-orfX using the indicated swab types. (E) Distribution of C_T values for SCCmec-orfX obtained with the BD Max MRSA assay in a clinical routine setting for samples that were confirmed by culture (concordant [con]) or were culture negative (discordant [dis]). Random selection of 49 concordant and 33 discordant results. Medians are shown. LQ, liquid; w/o ch, without charcoal; w/ch, with charcoal.