MICRO-ORGANISM PROFILES AND EMPIRICAL ANTIBIOTIC RECOMMENDATIONS FOR PERIPROSTHETIC JOINT INFECTIONS OF THE HIP FROM A LARGE, LONGITUDINAL STUDY

Introduction Periprosthetic joint infection (PJI) after total hip arthroplasty (THA) is a challenging complication with a 5-year mortality rate exceeding 20%. Treatment success is dependent on early appropriate empiric antibiotic treatment, which requires accurate knowledge of common pathogens and resistance patterns. This study evaluated the microbiology and antibiotic susceptibility of hip PJI to guide empiric therapy. Method All first-episode PJIs following primary THA (2016-2023) at three large tertiary hospitals were identified. PJIs were classified into ‘early’ and ‘late’ per International Consensus Meeting (ICM; <90 days or >90 days since primary) and Auckland classifications (<1 year or >1 year since primary). The causative organism(s) and antibiotic sensitivity were recorded and analysed for each case. Odds ratios were calculated. Results There were 160 PJI cases and 209 positive cultures. Early (<90 days, <1 year) PJIs were more likely to involve resistant microorganisms (ICM, Odds ratio (OR)=2.09, 95% confidence interval (CI) 1.07-4.14, p<0.05; Auckland, OR=2.34, CI 1.15-4.93, p<0.05) and also more likely to be polymicrobial (ICM, OR=2.68, CI 1.14-6.64, p<0.05; Auckland, OR=2.77, CI 1.09-7.92, p<0.05). Gram-negative microorganisms were also more prevalent in PJIs <90 days from primary (OR=2.77, CI 1.25-6.38, p<0.05). Flucloxacillin monotherapy provided poor coverage, particularly in early PJIs (<60%), however its efficacy was higher for late PJIs, achieving near 70% coverage. In contrast, Vancomycin monotherapy provided superior coverage across all cases (>80%). Combining gram-negative antibiotics such as co-trimoxazole/gentamicin with vancomycin increased coverage to >90% irrespective of infection timing. Conclusion Early PJIs are more likely to involve polymicrobial, resistant and gram-negative bacteria, therefore vancomycin plus a gram- negative agent is recommended for empiric therapy. Flucloxacillin may suffice for late PJIs but should be escalated to combination therapy if risk factors for resistant or gram-negative organisms are present.