A Multi-Year, Multi-Intensive Care Unit(ICU) Outbreak of Acinetobacter baumannii(ACB): Molecular Epidemiology and Case-Control Study.

R. Kaul*, L. Cork, H. Dedier, J. Burt, M. Garcia, M. Krajden, J. Conly.

The Toronto Hosp., Univ. Of Toronto, Toronto, On, Canada.

ACB is commonly isolated in the ICU setting, but estimates of its contribution to morbidity and mortality vary widely. Between 1990-1993 there was an increase of over 800% in the rate of respiratory ACB isolation from 5 ICUs in a tertiary care centre. An investigation was initiated and risk factors for ACB acquisition and the attributable mortality were delineated in a case-control study.

Conventional and quantitative cultures were obtained from ICU respiratory equipment before and during patient use and from the hands of 35 ICU staff. ACB isolates were characterized using pulsed-field gel electrophoresis (PFGE). A single strain accounted for 88% of environmental and 93.5% of patient isolates. ACB was isolated from "clean" temperature probes and respiratory equipment as well as 17% of staff hands. Control measures included gas sterilization of temperature probes, patient cohorting, respiratory therapy(RT) practice changes, and emphasis on good hand washing. Within 2 months respiratory ACB isolation rates returned to baseline.

In a case-control analysis, all patients colonized with ACB over a 4 month period were matched by APACHE II (acute physiology and chronic health evaluation) score to an equal number of controls from the same ICU. Risk factors for acquisition (p<0.05) were tracheostomy, ventilation for > 3 days, TPN use, dialysis, Xanthomonas maltophilia colonization and enteric feeding. Stepwise linear regression identified ventilation>3 days and enteric feeding as independently predictive for colonization. Mortality attributable to respiratory ACB acquisition was 50% (45.8% vs 22.9%). We conclude that this ICU outbreak of respiratory ACB acquisition likely resulted from multiple factors, including inadequate disinfection of temperature probes and respiratory equipment with secondary transmission on the hands. We hypothesize that respiratory ACB acquisition was increased by aspiration related to enteric feeding.