Co-Colonization with <i>Neisseria species</i> Is a Risk Factor for Prolonged Colonization with Multidrug-Resistant <i>Acinetobacter baumannii</i> in the Respiratory Tract

Abstract

SUMMARY: Multidrug-resistant Acinetobacter baumannii (MDRAB) colonization increases the risk of bacterial spread in the hospital setting. The impact of clinical factors, including antibiotic use, on prolongation of MDRAB colonization has not been investigated. Patients with respiratory tract MDRAB detected using culture were enrolled in this study. Long-term colonizers and short-term colonizers were defined as patients whose colonization periods were ＞30 days or 30 days, respectively. Clinical data were abstracted from medical records. MDRAB was isolated in 34 patients. There were 13 long-term colonizers and 9 short-term colonizers. Twelve patients were lost to follow-up and excluded from the study. There were no significant differences in average leukocyte counts, numbers of antibiotic classes administered, duration of antibiotic use in the 30 days following colonization, or rates of central catheterization or mechanical ventilation between the 2 groups. Long-term colonizers carried Neisseria species (spp.) more frequently in the 30 days following colonization than short-term colonizers (7/13 vs 1/9, p ＝ 0.01); however, this was not the case prior to colonization with MDRAB (5/13 vs 1/9, p ＝ 0.33). The 90-day MDRAB colonization rates for Neisseria-negative patients and Neisseria-positive patients were 10.0z and 83.3z, respectively (P ＜ 0.01). Prolonged MDRAB colonization in the respiratory tract was associated with Neisseria spp. co-colonization. Multidrug-resistantAcinetobacter baumannii (MDRAB) is an important pathogen in hospitalacquired infection. MDRAB colonization increases the risk of spread in the hospital setting (1). Many previous studies have investigated risk factors for acquisition of, or infection with MDRAB (2,3). Antibiotic use, dialysis, and prolonged intensive care unit stay have been identified as risk factors for colonization or infection with MDRAB (4-8). MDRAB has been associated with co-infecting organisms such as Staphylococcus or Pseudomonas species (spp.) (4). However, questions about the colonization period of MDRAB and the association of colonization with clinical or microbiological factors have not been answered. We experienced an MDRAB outbreak in our hospital from 2009 to 2011. The objectives of this study were to investigate the duration of MDRAB colonization in the respiratory tract after the acquisition of MDRAB, and the association between duration of MDRAB colonization and clinical or microbiological factors.All patients with MDRAB on throat or sputum cultures from 25 August 2009 through 17 March 2012 at the Teikyo University Hospital were included. The study site's institutional review board approved the review of the infection control data. Informed consent was waived. The samples were used to inoculate modified CHROMagar Acinetobacter plates (Chromagar, Paris, France), which were then incubated at 379 C and examined after 48 hours for oxidase-negative and bright salmon-red colonies that are indicative of MDRAB. Antimicrobial susceptibilities were analyzed using the curren...