Tehran University of Medical Sciences Journal of Medical Bacteriology 2251-8649 3 3-4 2015 10 13 32 39 EN Mahboobeh Naderi-Nasab Microbiology and Virology Research Center, Avicenna Research Institute & Department of Medical Bacteriology & Virology, Emam Reza Hospital, Faculty of Medicine, Mashhad University of Medical Sciences, Tehran, IR Iran. Ali Akbar Heydari Infectious Disease Departments, Imam Reza Hospital, Mashhad University of Medical Sciences, Mashhad, IR Iran. Valyolah Booryazadeh Infectious Disease Departments, Imam Reza Hospital, Mashhad University of Medical Sciences, Mashhad, IR Iran. Ahmadreza Zarifian Student Research committee, Mashhad University of Medical Sciences, Mashhad, IR Iran. Zahra Meshkat Microbiology and Virology Research Center, Avicenna Research Institute & Department of Medical Bacteriology & Virology, Ghaem Hospital, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, IR Iran. Monavar Afzalaghaei Mashhad University of Medical Sciences, Mashhad, IR Iran. 2015 10 12 2015 10 12 Introduction: Staphylococcus aureus colonization has been recognized as one of the most important risk factors for subsequent infections with this microorganism. In this study, we intended to identify all patients who were MRSA-positive upon admission and compare the prevalence of MRSA colonization on different days of study admitted in Imam Reza hospital in Mashhad, Iran. Methods: This cross-sectional study was done on 600 admitted patients in Infectious disease ward. Samples of patients were drawn from patients’ nares (and if they were culture negative, re-cultures were done on days 3, 7 and finally on discharge time. After identification of the isolates, their susceptibility to methicillin was evaluated. Before we collect nasal swabs, patients filled out a survey questionnaire. Results: S. aureus colonization early after hospitalization in infectious ward was observed in 39.8% (n=239) of patients, of which 59% (n=141) were resistant to methicillin. On the third day of admission, S. aureus new colonization rate was 15.8% (n=57), of which 87.7% (n=50) were methicillin resistant. On the seventh day, S. aureus were found in 13% (n=32) patients with 90.6% (n=29) were methicillin-resistant. Upon discharge, 8.2% (n=13) patients were S. aureus positive and 92.3% (n=12) were resistant to methicillin. Conclusion: Most of the carriers had the methicillin resistant strains of bacteria at the time of admission, and the number of colonized patients with resistant bacteria increased in time. The most common risk factors in methicillin-resistant S. aureus carriers were taking antibiotic, history of prior hospitalization and being an intravenous (IV) drug abuser. https://jmb.tums.ac.ir/index.php/jmb/article/view/35 https://jmb.tums.ac.ir/index.php/jmb/article/download/35/30