Case of the Month - August 2016

A prosthetic hip infection caused by linezolid-resistant Staphylococcus epidermidis

Heidi Orth, Marthinus Senekal and Catherine Samuel - Clinical Microbiologists, PathCare; Adriaan van Huyssteen, Orthopaedic surgeon, Panorama Medi-Clinic hospital

Linezolid resistance in staphylococci is rarely observed in our setting. An increase in the therapeutic use of linezolid may cause selective pressure and lead to the emergence of resistance. We report a case of prosthetic hip joint infection caused by a linezolid-resistant Staphylococcus epidermidis. A 60-year old female had a total hip replacement in August 2013. A joint revision was performed in April 2014 due to loosening of the acetabular component. Cefuroxime was administered as peri-operative prophylaxis. She also received amoxicillin-clavulanate treatment for an E. coli urinary tract infection. The patient was subsequently taken back to theatre three times with recurrent dislocation of the prosthesis due to avulsion of the gluteus medius. A second revision of the left total hip replacement was performed in September 2014. At surgery there was no evidence of infection but amoxicillin-clavulanate was administered for post-operative wound infection. Fluid aspirates from the draining wound and tissue specimen cultures showed no growth. The synovial fluid white cell count was 0.5 x109/l with 13% neutrophils. In November 2014, following another dislocation, a third revision was performed due to rupture of the external rotator muscles. Intra-operatively, there was no evidence of deep-seated infection. Post-operatively, amoxicillin-clavulanate was again initiated for a wound infection indicated by a persistently draining wound and CRP of 45 mg/l. The clinicians noted an initial improvement on amoxicillin-clavulanate , but the wound again began to drain fluid and the antimicrobial therapy was changed to ciprofloxacin, cotrimoxazole and rifampicin. Two weeks after the third revision, the patient underwent debridement and joint washout. Treatment was changed to linezolid and ciprofloxacin. Large amounts of purulent fluid were drained and the synovial fluid aspirate showed a white cell count of 32 x 109/l with 88% neutrophils. Other infective parameters included a blood white cell count of 8.1 x 109/l; CRP 323mg/l and ESR 101mm/hr. Two days post-debridement, rifampicin was added to the linezolid and ciprofloxacin as empiric treatment of prosthetic joint infection.

Question 1 How is the aetiology of prosthetic joint infection determined?

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