Epidemiology of Staphylococcus aureus in Italy: First nationwide survey, 2012

A 3-month epidemiological study to determine the prevalence and antibiotic resistance ofStaphylococcus aureus nosocomial infections was performed in 52 centres throughout Italy in 2012. Atotal of 21,873 pathogens were analysed. The prevalence of S. aureus among all nosocomial pathogensisolated in that period was 11.6% (n = 2541), whilst the prevalence of methicillin-resistant S. aureus(MRSA) among the S. aureus was 35.8% (n = 910). All tested antimicrobials demonstrated 92.2%susceptibility against methicillin-susceptible S. aureus, with the exception of clindamycin (89.7%) anderythromycin (84.2%). Among MRSA, percentages of resistance ranged from 12.6% to >39% fortetracycline, rifampicin, clindamycin and gentamicin; higher percentages were found for erythromycin(65.4%) and fluoroquinolones (72.3–85.8%). Overall, the glycopeptide minimum inhibitory concentration(MIC) distribution showed that 58.3% of strains possessed MICs of 1–2 mg/L and few strains werelinezolid- or daptomycin-resistant. Molecular characterisation was performed on 102 MRSA selectedfrom Northern, Central and Southern regions. Five major clones were found: Italian/ST228-I (t001-t023-t041-t1686-t3217), 33.3%; USA500/ST8-IV (t008), 17.6%; E-MRSA15/ST22-IVh (t020-t025-t032-t223),16.7%; USA100/ST5-II (t002-t653-t1349-t2164-t3217-t388), 14.7%; and Brazilian/ST239/241-III (t030-t037), 3.9%. Five PVL-positive CA-MRSA isolates, belonging to USA300 and minor clones, were alsoidentified. In conclusion, this first nationwide surveillance study showed that in Italy, S. aureus infectionsaccounted for 11.6% of all nosocomial infections; MRSA accounted for approximately one-third of theS. aureus isolates and these were multidrug-resistant organisms. Five major MRSA epidemic clones wereobserved and were inter-regionally distributed, with ST228-SCCmecI becoming predominant.