Nosocomial Acinetobacter pneumonia

Abstract

Acinetobacter spp. (A. baumannii is the prevalent genomic species, but others may cause infection) has become an increasingly important cause of nosocomial pneumonia, particularly in mechanically ventilated patients (VAP). This organism has intrinsic resistance to some antimicrobials but easily acquires resistance to many others; Acinetobacter spp. can survive for long periods of time in the environment. All of these characteristics have contributed to protracted outbreaks associated with significant morbidity and mortality. High rates of colonization are found in debilitated hospitalized patients. Infecting or colonizing organisms in nosocomial infections are more likely to be from cross-transmission or from the hospital environment than from endogenous sources. VAP caused by Acinetobacter spp. is emerging as a prominent hospital complication. The incidence of this microorganism varies from site to site, but it is the second commonest aetiological agent among the gram-negative bacteria. Longer periods of hospitalization, longer time on mechanical ventilation and prior use of antibiotics are the recognized factors increasing the risk of VAP due to Acinetobacter spp. Treatment needs to clearly differentiate infection from colonization, and the agents with the most antimicrobial activity are imipenem/cilastatin, amikacin, colistin, ampicillin/sulbactam and tigecycline. Monotherapy can be adequate if the patient does not have significant comorbidities. Infection control procedures have a major role to play in preventing transmission of this microorganism. Emphasis on initial control measures should, however, be on strict isolation of infected or colonized patients to limit dissemination of outbreak strains in the environment. The variety of potential sources of contamination with Acinetobacter spp. in the hospital environment makes control of these outbreaks one of the more difficult challenges. Persistence of Acinetobacter spp. in the environment provides ample opportunities for contamination of patients and staff and may explain continuing long-term outbreaks.