Ventilator associated pneumonia: microbiology and identification of antimicrobial resistance pattern by disk-diffusion and E.test methods

Background: ventilator- associated pneumonia (VAP) continues to complicate the course of 8-28 % patients receiving mechanical ventilation. The mortality rate for VAP is high, ranges from 24-50% and can reach 76% in some specific settings or when lung infection is caused by high risk pathogens. The etiologic agents widely differ according to the population of patients in an intensive care unit, duration of hospital stay, and prior antimicrobial therapy. Because appropriate antimicrobial treatment of patients with VAP significantly improves outcome, more rapid identification of infected patients and selection of antimicrobial agents represent important clinical goals. Our goal was determination of the VAP incidence, identification of common pathogenic causes and determination of antimicrobial resistance pattern by disk-diffusion and E.Test methods. Materials and methods: In an observational study we evaluated the microbiology and antimicrobial resistance pattern of VAP in medical Intensive Care Units (ICUs) of 2 teaching hospitals from January 2005 to January 2006. Diagnostic criteria for VAP were the radiographic appearance of a new or progressive and persistent pulmonary infiltrate in conjunction with at least 2 of the following criteria: purulent respiratory secretions, temperature > 38.5 °c or < 35°c, leukocyte count > 10,000 mm3 or < 1,500/mm3. Mini–BAL was planned for all of suspicious cases. For each causative pathogen, antibiotic susceptibility was determined by disk-diffusion and E.Test methods. Results: Among 114 patients under mechanical ventilation, 6 patients (5.3%) had a VAP episode, 3 patients in each hospital. In VAP patients the mean days of hospitalization were 26.3 days (± 20.92) and ICU stay were 22.8 days (± 21.53). There was a significant statistical correlation between use of H2 blockers and VAP (P < 0.05). Pseudomonas aeruginosa and Klebsiella pneumonia were isolated by mini-BAL ( > 104cfu/ml) in 6 patients (each pathogen in 3 cases). Antimicrobial susceptibility pattern were determined by disk-diffusion and E.Test methods and all of pathogens except one (pseudomonas aeruginosa) were resistant to ceftriaxone and ceftazidime. Conclusion: This study showed the increasing incidence of resistance to third and fourth generations of cephalosporins among gram negative bacilli that has occurred in parallel with increasing use of these drugs in our ICUs. More judiciouse use of antibiotics will be necessary to limit this trend.