Authors: V. Muttagi and J. R. Cantey,
Title: Epidemiology and Microbiology of Prosthetic Joint Infections at the Medical University of SC
Address: Division of Infectious Diseases, Medical University of SC, Charleston, SC
Purpose: Most published literature concerning prosthetic joint infections concern risk factors and/or the best strategies for surgical management of the infected arthroplasty. The only recent comprehensive assessment is that of Barbari et al. (CID 27:1247-54; 1998) in which 462 patients with prosthetic joint infections were reviewed. Race has not been assessed as a risk factor in any prior report. The Department of Orthopedics at MUSC places approximately 400 prosthetic joints each year and also serves as a referral center for infected joint prostheses for the lower half of South Carolina. The purpose of this study was to assess risk factors and microbiology of infected joint prosthesis at MUSC.
Methods: The medical records department at Medical University Hospital searched using the ICD-9 code 99666 (infected joint prosthesis) for the interval July 1, 1999 to September 30, 2002. Prospective data collection began October 1, 2002. Information recorded included patient history, demographics, risk factors, microbiology of infected joint fluids and tissues, surgical procedures, medical treatment and outcome.
Results: As of this date we have information for 90 infections in 84 patients. 61% were female. Six patients were =80 years of age. 39% of infections occurred in blacks. 45% of infected joints were knees. 21% of patients were diabetic, 58% of whom were black. 9% of patients had rheumatoid arthritis, all were female. 31 patients had S. aureus infections, 9 of which were methicillin resistant. All but one of the MRSA infections were polymicrobial. Coagulase negative infections numbered 29, 17 of which were methicillin resistant. Enterococcus species was isolated in 7 patients and all were polymicrobial. Group B Streptococcus agalactiae was isolated from 6 patients, five were female. 23 patients had polymicrobial infections. Polymicrobial infections included a gram positive organism(s), and in 14 gram, negative organisms. 13 patients grew no organism. Data collection is ongoing. Multivariant analysis of risk factors is planned.
Discussion: Diabetes was our major risk factor (21%) versus 6.3% at Mayo. Black race was over represented for their percent of SC population (30.8%) and blacks were also over represented among diabetics (58%). Staphylococci were isolated in 66% of our patients versus 41% at Mayo. Methicillin resistance was 43% overall. Group B streptococcus (7%) and enterococcus incidence (8%) has not been reported elsewhere,
Significance: Patients in SC with joint prosthesis infection are more commonly diabetic and/or black. The frequent isolation of antibiotic resistant organisms has implications for empiric therapy. Risk factors for and possible role of group B streptococci and enterococci will be discussed.