CONTRIBUTION OF GENEXPERT MRSA-SA SSTI- ESSAY TO FAST DIAGNOSIS OF MRSA AND MSSA POSITIVE PROSTHESIS JOINT INFECTION.

Introduction

Rapid identification of bacteria from extemporaneous samples would greatly help management of prosthesis joint infection. The aim of the present retrospective study was to evaluate a new molecular assay (GeneXpert MRSA-SA SSTI (Cepheid)) for detecting Staphylococcus aureus (SA) and methicillin resistance directly from bone and joint samples in less an hour (58 minutes).

Material et method

Retrospective study using 91 frozen samples (76 patients) of joints (n=24), bone biopsies (n=42) and tissue biopsies (n=25):

1. -

   SA positive samples: n=72 (methicillin susceptible SA (MSSA), n=63; methicillin resistant MRSA, n=9)

2. -

   SA positive samples: n=19

The results were compared with routine results (culture in solid and liquid medium, identification and susceptibility test) from each participating lab.

Results

The 72 SA positive samples gave:

1. -

   68 concordant positive results comprising:

   1. .

      9 MRSA positive samples,

   2. .

      56 MSSA positive samples,

   3. .

      3 MSSA positive samples, positive for SA but with inconclusive results for methicillin resistance.

2. -

   4 negative discordant results for MSSA positive samples

The 19 SA negative samples gave:

1. .

   16 concordant negative results

2. .

   3 SASM positive results for negative culture of samples obtained from patients with other MSSA positive deep or superficial samples, suggesting a higher sensitivity for the GeneXpert test than culture in these cases.

Sensitivity and specificty for bone and joint samples:

Se=68/72=94.4%

Sp=16/16=100%

Conclusion

The GeneXpert MRSA-SA SSTI assay provides 58-minute detection of MSSA and MRSA directly from bone and joint samples. Sensitivity and specificity were excellent in this preliminary study. This test may enable real-time peroperative diagnosis of Staphylococcus aureus, which could be very useful in the field of revision surgery. Further prospective studies should be done to accurately determine the PPV, NPV, and clinical and pharmaco-economic impact of this test in the setting of prosthesis joint infection.