We described case-control findings in two A. baumannii outbreaks at unrelated tertiary-care hospitals in Kentucky. Although the outbreaks occurred in different cities, risk factors for A. baumannii acquisition were similar. For both facilities, the majority of initial positive specimens came from a respiratory site; the second most common initial positive culture site for both facilities was a wound. On univariate analysis, we found an association between mechanical ventilation, presence of a tracheostomy, and ICU admission with recovery of A. baumannii at both institutions; multivariate analysis demonstrated an association with mechanical ventilation in both facilities and nonsurgical wounds in Hospital A.
At both facilities, the population of cases in whom A. baumannii
was recovered had a wide age range. Our findings are consistent with a review performed by Villegas et al., which identified respiratory and nonrespiratory outbreaks that occurred in pediatric and adult populations.7
Stephens et al. also identified an age range of 22–85 years in patients diagnosed with MDR A. baumannii
who were treated in an acute and long-term-care facility within the same building complex.8
This finding may be consistent with the discovery that A. baumannii
pneumonia is related to contamination during airway management, and does not seem to be associated with severity of comorbid disease at hospitalization.9
On multivariate analysis, the requirement for mechanical ventilation was a risk factor for recovery of A. baumannii
at both facilities; presence of a nonsurgical wound was also associated with recovery of A. baumannii
at Hospital A. These findings are consistent with previous research that has demonstrated respiratory tract infections and wounds to be a common source for recovery of Acinetobacter
Although we did not find this association at Hospital B to be statistically significant, we suspect it might have been the result of inconsistencies in chart documentation.
The role of mechanical ventilation as a risk factor for Acinetobacter
colonization or infection has been reported in several other studies. Robenshtok et al. demonstrated an association between mechanical ventilation and recovery of Acinetobacter
and Sofianou et al. identified an association between length of mechanical ventilation and ventilator-associated pneumonia.16
Previous research has determined that the risk for a positive Acinetobacter
culture is associated with factors that increase the degree of airway manipulation, and that comorbidity and severity of illness do not play an important role in Acinetobacter
infection and colonization.9
We hypothesize that patients requiring mechanical ventilation not only have an increased risk for becoming colonized or infected with Acinetobacter
, but also that they have an increased risk for transmitting Acinetobacter
to other patients in the same area of the hospital after they become colonized or infected. This theory is based on findings from previous Acinetobacter
outbreak investigations, during which respiratory secretions have been demonstrated to increase environmental contamination.13,17
Patients with extended lengths of stay have more care provided from physicians, nurses, and respiratory therapists, and, therefore, have increased opportunity to become infected or colonized with Acinetobacter
. The interaction between the patient and the health-care worker might increase the opportunity for hand contamination and subsequent spread of the Acinetobacter
organism between patients. Further, contamination of the patient room occurs most commonly in rooms containing patients with colonized or infected wounds.18
Such patients, after becoming infected or colonized, might therefore serve as a source of infection for other hospitalized patients.
During the process of caring for patient wounds, health-care workers might contaminate either their hands or the patient environment. In fact, one study demonstrated that cross-transmission was responsible for two-thirds of nosocomial Acinetobacter
transmission in the ICU.14
In addition, a previous outbreak revealed that the point-prevalence of patients testing culture-positive for MDR Acinetobacter
in a given hospital was the only risk factor independently associated with Acinetobacter
As such, increased interaction between patients and health-care workers might increase the likelihood for transient hand contamination of health-care workers and the spread of Acinetobacter
to other patients.
Spread of Acinetobacter
through hand carriage has been implicated during previous Acinetobacter
However, hand carriage appears to be limited and might occur only immediately after completion of patient care and before use of an alcohol-based sanitizer.21
In addition, patients colonized or infected with Acinetobacter
typically only spread it to their immediate surroundings.22
Following infection control precautions such as wearing gowns and gloves prior to care of patients infected or colonized with Acinetobacter
, and performing correct hand washing when caring for ventilated patients and patients with nonsurgical wounds is, therefore, particularly important. As such, during the outbreaks described at both facilities, infection control staff emphasized the importance of wearing gowns and gloves to patient care staff when caring for patients in whom A. baumannii
This study had two limitations. First, the requirement that controls have a length of stay at least as long as the mean case length of stay prior to recovery of Acinetobacter rendered us unable to evaluate the potential association between length of stay and a positive Acinetobacter culture. This requirement may also confound our analysis of antibiotic exposure as a risk factor. Because antibiotic doses were recorded for the two weeks prior to day 14 of hospitalization for Hospital A and day 17 of hospitalization for Hospital B, 14 days of antibiotic exposure could always be documented for control subjects. Conversely, for cases, antibiotic exposure was documented two weeks prior to positive culture—a period that often included fewer than 14 days of hospitalization. Second, we had a limited sample size in Hospital A to detect differences among risk factors that might have been associated with recovery of A. baumannii.