Background and purpose: Hospital-acquired (nosocomial) pneumonia (HAP) is the most common type of infection in patients in intensive care units (ICU) which results in high rate of mortality. Due to differences in type of microorganisms and their resistance pattern, this study was conducted to determine the profile of microorganisms and their resistance pattern to initiate more effective empirical therapy.

Materials and methods: This prospective study was conducted among all patients admitted to three ICUs of Imam Khomeini Hospital for the occurrence of pneumonia between January 2011 and August 2012. Sample collection for microbiological analysis was done by ETA (endotracheal aspiration) and BAL (bronchoalveolar lavage) methods. Antimicrobial susceptibility test was determined by Disk Diffusion and Broth Dilution methods according to CLSI (Clinical and Laboratory Standards Institute) guidelines.

Results: Three hundred and eight patients from three ICUs were included in the study. The incidence of nosocomial pneumonia was 11.4%, including 91.4% VAP (ventilator-associated pneumonia) and 8.6% Non-VAP. The most common microorganisms isolated were Acinetobacterspp (22%) and Staphylococcus aureus (14.6%). Thirty percent of Acinetobacterspp were resistant to all antimicrobial agents. Ceftazidime was the most effective antibiotic (resistance rate= 22.2%). All isolated Acinetobacters were resistant to ciprofloxacin and ceftriaxone. Staphylococcus aureus isolates, were 50% and 33.3% resistant to vancomycin with Disk Diffusion and Broth Dilution, respectively. Conclusion: We observed a high prevalence of Acinetobacter spp. and Staphylococcus aureus (14.6%). According to the culture/sensitivity results the most effective antibiotics could be Ceftazidime, Tobramycin and Ofloxacin. However, using Ceftriaxone and Ciprofloxacin is not recommended until their efficacy is documented in future studies.