Background: Nosocomial pneumonia (NP) is an important cause of morbidity and mortality in hospitalized patients. Acinetobacter baumannii is one of the common causative pathogens in NP. The prevalence of multi-drug resistance in A. baumannii has been increasing. The information on clinical features and clinical courses of A. baumannii NP in Thai patients are limited.
Objective: To determine the clinical features, risk factors and clinical courses of A. baumannii NP in Thai patients hospitalized in tertiary care hospitals in Thailand.
Material and Method: This was a prospective, hospital-based, active surveillance study on hospital-acquired pneumonia (HAP) and ventilator-associated pneumonia (VAP) in adults hospitalized in 12 tertiary care hospitals in Thailand between 2008 and 2009.
Results: There were 651 NP patients. A. baumannii was the most common cause of NP in 198 patients (30.4%). Most of NP patients were males with median age of 71 years. About 80% had late onset NP with the median duration of 10 days after admission in both A. baumannii and non-A. baumannii NP. Most of NP occurred in patients hospitalized in general medical wards. Most of the features of NP in A. baumannii NP and non-A. baumannii NP were not significantly different. The initial antibiotics prescribed were concordant in about 50% of the patients in both groups. Colistin was usually prescribed to the patients who received antibiotic modifications. The initial clinical responses in A. baumannii NP were less favorable than those in non-A. baumannii NP. The mortality rate in A. baumannii NP seemed to be more than that in non-A. baumannii NP. There was a trend of more persistence of pathogen in A. baumannii NP. Most isolates of A. baumannii were resistant to
antibiotics including carbapenems. The patients with extensive drug resistant A. baumannii NP had less favorable responses than NP due to other bacteria, including non-extensive drug resistant A. baumannii. VAP, NP developed in medical ICU and
NP with bilateral lung involvements on chest X-ray were associated with A. baumannii as the isolated pathogen.
Conclusion: A. baumannii is the most common causative pathogen for NP in tertiary care hospitals in Thailand and most of A. baumannii isolates were resistant to many antibiotics including carbapenems. The hospitalized patient in tertiary care hospitals with VAP, or NP that was developed in medical ICU, or NP with bilateral lung involvements on chest x-ray was likely to be due to A. baumannii. Many NP patients received inappropriate initial antibiotic regimens leading to a high mortality.

Keywords: Acinetobacter baumannii, Nosocomial pneumonia, Hospital-acquired pneumonia, Ventilator-associated pneumonia