It is important to know the spectrum of the microbial aetiology of prosthetic joint infections (PJIs) to guide empiric treatment and establish antimicrobial prophylaxis in joint replacements. There are no available data based on large contemporary patient cohorts. We sought to characterize the causative pathogens of PJIs and to evaluate trends in the microbial aetiology. We hypothesized that the frequency of antimicrobial-resistant organisms in PJIs has increased in the recent years. We performed a cohort study in 19 hospitals in Spain, from 2003 to 2012. For each 2-year period (2003-2004 to 2011-2012), the incidence of microorganisms causing PJIs and multidrug-resistant bacteria was assessed. Temporal trends over the study period were evaluated. We included 2524 consecutive adult patients with a diagnosis of PJI. A microbiological diagnosis was obtained for 2288 cases (90.6%). Staphylococci were the most common cause of infection (1492, 65.2%). However, a statistically significant rising linear trend was observed for the proportion of infections caused by Gram-negative bacilli, mainly due to the increase in the last 2-year period (25% in 2003-2004, 33.3% in 2011-2012; p 0.024 for trend). No particular species contributed disproportionally to this overall increase. The percentage of multidrug-resistant bacteria PJIs increased from 9.3% in 2003-2004 to 15.8% in 2011-2012 (p 0.008), mainly because of the significant rise in multidrug-resistant Gram-negative bacilli (from 5.3% in 2003-2004 to 8.2% in 2011-2012; p 0.032). The observed trends have important implications for the management of PJIs and prophylaxis in joint replacements.

PurposeWe wanted to improve the diagnosis of implant-related infection using molecular biological techniques after sonication.MethodsWe studied 258 retrieved implant components (185 prosthetic implants and 73 osteosynthesis implants) from 126 patients. 47 patients had a clinical diagnosis of infection (108 components) and 79 patients did not (150 components). The fluids from sonication of retrieved implants were tested in culture and were also analyzed using a modified commercial PCR kit for detection of Gram-positive and Gram-negative bacteria (GenoType BC; Hain Lifescience) after extraction of the DNA.Results38 of 47 patients with a clinical diagnosis of infection were also diagnosed as being infected using culture and/or PCR (35 by culture alone). Also, 24 patients of the 79 cases with no clinical diagnosis of infection were identified microbiologically as being infected (4 by culture, 16 by PCR, and 4 by both culture and PCR). Comparing culture and PCR, positive culture results were obtained in 28 of the 79 patients and positive PCR results were obtained in 35. There were 21 discordant results in patients who were originally clinically diagnosed as being infected and 28 discordant results in patients who had no clinical diagnosis of infection.InterpretationFor prosthetic joint infections and relative to culture, molecular detection can increase (by one tenth) the number of patients diagnosed as having an infection. Positive results from patients who have no clinical diagnosis of infection must be interpreted carefully.

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In our hospital, septic arthritis is primarily acute, monoarticular, and monomicrobial; affects higher joints, is caused by S. aureus, and occurs in adult patients with underlying diseases. Outcome is good in most patients, although more than 25% of cases had articular sequels.

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