Microbiology of cardiac implantable electronic device infections

The aim of the study was to describe the microbiological findings of cardiac implantable electronic devices (CIEDs) infection in the 2000-2011 period at the Cardiology Unit of New Santa Chiara Hospital in Pisa (Italy). Removed CIED leads and pocket material were seeded on solid media and isolates tested for antimicrobial susceptibility with the Kirby Bauer method. Electrodes from 1204 patients were analysed and 854 (70.9%) tested positive. In 663 (77.6%) cases only one species was isolated, in 175 (20.5%) two species, and in 14 (1.8%) >2 species. In 116 cases material from the pocket was also cultured. The result was consistent with that from the electrodes in 69 (59%) cases. In 359 cases a blood sample was also obtained for culture. The result was consistent with that from the leads in 124 (35%) cases. A total of 1068 strains were isolated from electrodes. Gram-positive organisms were most frequently isolated (92.5% of isolates); particularly, coagulase-negative staphylococci (CoNS), mainly Staphylococcus epidermidis, in 69% of cases and Staphylococcus aureus in 13.8%, Gram-negative rods in 6.1%, yeasts in 1% and molds in 0.4%. Overall, Oxacillin resistance was 30%, in particular 33% among CoNS and 13% among S. aureus. Oxacillin resistance and quinolones resistance have increased in the period 2006-2011 with respect to the 5 years before. Seventeen percent of Enterobacteriaceae strains had a phenotype compatible with extended spectrum beta-lactamase expression. Culture of the leads offers the possibility of an aetiological diagnosis in the majority of cases. When material from the pocket can be obtained, the microbiological result is often consistent with that from the electrodes, while species isolated from blood cultures are often different and more likely to be the result of contamination. Cardiac implantable electronic device infection is more often monomicrobial, CoNS are most frequently isolated and S. epidermidis is largely the main single agent. Very early infections were associated with S. aureus infection. The pattern of susceptibility to antimicrobials is in general that of community-acquired infections, although oxacillin resistance and quinolones resistance has increased in the last 5 years.