Background: Staphylococcus aureus is one of the important pathogens can cause infections in hospitals specially in intensive care units (ICU). It seems that nasal carriage is important risk factor for developing l infection at ICU units. This study was designed to investigate the frequency of S. aureus nasal carriage and its virulence in patients admitted to ICU units in Vali-Asr hospital at Arak university of medical sciences.

Materials and Methods: In this cross-sectional study, nasal swab samples were obtained from all the patients hospitalized in ICU unit of Vali-Asr hospital from July-December 2014 at admission. After identification, methicillin resistance and the frequency of pvl and acme genes determined by PCR. Demographic data were collected using questionnaire and were analysed using SPSS 20 software.

Results: Out of 390 patients, 81(20.8%) and 31(12.9) patients had been colonized with MSSA and MRSA, respectively. The result of culture was negative for 278 patients (71.3%). 77.4% of MRSA and 54.3% of MSSA isolates were positive for acme gene. Also, 11.11% of and 6.45% of MSSA MRSA isolates were positive for pvl gene.

Conclusion: The application of medical supportive devices like cv line, ventilator, history of surgery operation and antibiotic use significantly was associated with S. aureus nasal carriage. High prevalence of S.aureus shows that these bacteria settled in the hospital. Hence, infection control measures must be performed to reduce the risk of hospital infection.