Abstract
Aim
To determine whether rep-PCR genotyping can improve the diagnosis of coagulase-negative staphylococci(CoNS)bone and joint infection relative to the standard method based on phenotypic identification.
Method
Observational study comparing diagnostic tests (January 2011-March 2015), including all orthopaedic surgery patients with clinically suspected infection and ≥2 surgical specimens culture-positive for CoNS. Data collection included epidemiologic and clinical information, current clinical signs of suspected infection, and microbiological information. Each CoNS strain was analyzed by both methods (phenotyping, VITEK and API;and genotyping, rep-PCR). In accordance with current IDSA guidelines, CoNS strains identified as identical in ≥2 samples within the same surgical episode were considered pathogenic. The results of the two techniques were compared and statistically analyzed.
Results
255 CoNS isolates from 52 surgical episodes with suspected infection in 42 patients (55% male, mean age 61.5±20.6 years) were included. The patients' Charlson comorbidity index was 0.7±1.1. Implanted material was present in 79% of episodes and the surgical site had undergone previous surgery in 93%. CoNS infection was diagnosed by phenotyping in 73% of patients (mean, 2.2±1.3 different strains identified per episode)and 77% by rep-PCR analysis(mean, 1.8±0.6 different strains per episode). The kappa index of concordance was 0.59±0.14 (p<0.01). In patients in whom CoNS was considered not a cause of infection by phenotyping, 37% were considered infective agents by genotyping, accounting for 10%of the total.
Conclusions
The two diagnostic methods showed moderate agreement in the diagnosis of postoperative bone and joint infection. Rep-PCR had a somewhat higher capacity for identifying CoNS strains. Rep-PCR could be of value as a complementary technique to phenotyping when the latter technique identifies CoNS strains as being non-pathogenic.
