Predominance of Gram-negative Bacteria in Orthopaedic Implant Infections: A Hospital-Based Cross-Sectional Study in Western Kenya

Abstract

Background: Orthopaedic implant infections remain a major clinical challenge, often complicated by biofilm formation that impairs antibiotic penetration and delays healing. Globally, the infection rate is about 13% in primary implantation and 40% in revision surgeries. In Kenya, the infection rate is about 13.8%. Gram-negative bacteria are increasingly recognised as key pathogens, yet data from Kenya remain limited. Materials and Methods: This cross-sectional study was conducted at Kakamega County Teaching and Referral Hospital (KCTRH) between January 2023 and March 2024. A total of 191 patients with clinically suspected orthopaedic implant infections were enrolled in the study. Purposive sampling was used to recruit participants. Specimens (wound swabs) were inoculated on blood, MacConkey, and chocolate agar and incubated aerobically at 37°C for 24–48 hours. Bacterial identification and antimicrobial susceptibility testing were performed using standard biochemical tests and the VITEK 2 Compact system (bioMérieux, France). Sample size was estimated using Fisher’s formula, assuming an expected prevalence of 20%, a 5% margin of error, and a 95% confidence interval. Results: Overall, the most prevalent Gram-negative species were Klebsiella pneumoniae (29.3%), Escherichia coli (17.9%), Pseudomonas aeruginosa (16.9%), and Citrobacter freundii (10.3%). Other Gram-negatives, including Proteus mirabilis, Providencia stuartii, Raoultella ornithinolytica, and Klebsiella oxytoca, were detected in <2.2% of cases. Staphylococcus aureus (14.9%) and Staphylococcus epidermidis (2.1%) were the only Gram-positive species. Infections occurred mainly in the early (47.67%) and delayed (50.78%) phases, with Klebsiella pneumoniae predominating in both phases. High resistance was observed to ampicillin, penicillin, vancomycin, and several cephalosporins, while amikacin and piperacillin-tazobactam showed the highest sensitivity. Conclusion: Gram-negative bacteria, predominantly Klebsiella pneumoniae, were a major causative agent of orthopaedic implant infections, suggesting a shift from Staphylococcus aureus. The resistance patterns emphasise the need for routine, individualised AST to guide effective therapy.