Sources of multidrug-resistant Acinetobacter baumannii and its role in respiratory tract colonization and nosocomial pneumonia in intensive care unit patients.

Background: Multidrug-resistant Acinetobacter baumannii (MDRAB) is an important and emerging hospital-acquired pathogen worldwide. This study was conducted to identify the sources of MDRAB and its role in respiratory tract colonization and nosocomial pneumonia in intensive care unit (ICU) patients.

Methods: We conducted a prospective active surveillance study of MDRAB in three ICUs at a Chinese Hospital from April to August 2011, to identify the sources of MDRAB and its role in respiratory tract colonization and nosocomial pneumonia.

Results: One hundred and fourteen (13.0%) MDRAB isolates were detected from 876 specimens, with a sensitivity of 11.6% (55/474) in screening of the pharyngeal and tracheal swabs, and 14.7% (59/402) of the sputum/endotracheal aspirates. MDRAB colonization/infection was found in 34 (26.8%) of 127 patients, including 16 (12.6%) cases of pure colonization and 18 (14.2%) cases of pneumonia (two pre-ICU-acquired cases of pneumonia and 16 ICU-acquired cases of pneumonia). Previous respiratory tract MDRAB colonization was found in 22 (17.3%) patients: eight (6.3%) were pre-ICU-acquired colonization and 14 (11.0%) ICU-acquired colonization. Of eight pre-ICU-colonized patients, five were transferred from other wards or hospitals with hospitalization > 72 hours, and three came from the community with no previous hospitalization. Overall, 6/22 colonized patients presented with secondary pneumonia; only two (9.1%) colonized MDRAB strains were associated with secondary infections. Respiratory tract MDRAB colonization had no significant relationship with nosocomial pneumonia (P = 0.725). In addition, acute respiratory failure, mechanical ventilation, renal failure, and prior carbapenem use were risk factors for MDRAB colonization/infection.

Conclusions: A high proportion of cases of MDRAB colonization/infection in ICU patients were detected through screening cultures. About one-third were acquired from general wards and the community before ICU admission. The low incidence of MDRAB colonization-related pneumonia questions the appropriateness of targeted antibiotic therapy.