Spread of a methicillin-resistant staphylococcus aureus clone isolated from bacteremia in elderly patients in a Brazilian general hospital

ABSTRACT

A study of the genomic diversity of MRSA strains isolated from elderly patients with infection/colonization in three repeated prevalence, cross sectional studies was performed in the 1999-2000 period. In this study, 13 MRSA isolates from blood cultures and 5 from rectal and nare cultures were obtained from 18 patients (13 elderly and 5 adults). Most of the patients were being treated with two or more antimicrobials (83.3%), had insertion of invasive devices (88.9%) and were managed in ICU (Intensive Care Unit) and/or surgical units (66.7%). MIC (Minimum Inhibitory Concentration) data showed that 88.9% of the MRSA strains were resistant to high concentrations of oxacillin (MIC > 256 ìg/mL), 94.5% of the MRSA carried the mecA gene in their genome, and most (65.0%) of the isolates were indistinguishable according to their DNA finger­printing generated by PFGE (Pulsed-field gel electrophoresis). Although PFGE typing was performed with a few MRSA isolates, our results demonstrate that one MRSA clone was associated with infection/colonization in patients with an obvious connection among five out of eleven patients who stayed in the same clinic and ICU during the same period. Hospital acquired infection, a major “silent epidemy”, is associated with prolonged hospital stay and high mortality rate and its cause must be better evaluated.