Out of Drugs, Out of Time: Clinical and Infection Control Aspects of a Multidrug-resistant Acinetobacter baumannii Outbreak in a Neonatal Intensive Care Unit

Background: Multidrug-resistant Acinetobacter baumannii, was first isolated from a patient in the Neonatal Intensive Care Unit (NICU) at a Level 3, 36-bed, University-affiliated teaching hospital in Detroit. Subsequently, A. baumannii was recovered from 5 additional infants. Only one susceptible A. baumannii infection had been recorded in this NICU in the three years prior to this outbreak.

Objective: To describe multi-drug resistant Acinetobacter baumannii outbreak in a neonatal intensive care unit.
Methods: A retrospective chart review was performed for each neonate with an identified multidrug-resistant A. baumannii isolate during the outbreak from 11/2008 to 1/ 2009.  Demographic and clinical data including maternal intrapartum data were recorded. Data collection occurred in conjunction with an infection control investigation being conducted by hospital epidemiology. 

Results: A total of six infants, aged 10 to 197 days at culture positivity, had resistant strains of A. baumannii isolated from eye, respiratory and blood samples.  All of the infants were premature, with gestational ages ranging from 23 to 30 weeks.  The birth weights of all of the infants were 1000 grams or less.  The index case was transferred in from an outside hospital.  Five of the six infants had prolonged ventilatory support, all had central venous catheters, and all were exposed to broad spectrum antibiotics prior to their culture-positive status, including one exposed to 12 days of meropenem therapy.  The clinical spectrum of disease in the six infants varied from colonization to conjunctivitis, ventilatory associated pneumonia and bacteremia.  Five of the six infants were alive on follow up, one of whom was discharged home.  One infant died from causes not attributed to the organism.  All six isolates were uniformly resistant to ampicillin, cephalosporins, including cefepime, ciprofloxacin, gentamicin, amikacin and meropenem.  Two of six isolates retained susceptibility to tobramycin, and 5 of six had moderate susceptibility to ampicillin/sulbactam.  Five isolates tested for colistin susceptibility by E-test were susceptible.  The range of tigecycline minimum inhibitory concentrations by E-test for five isolates was 4 to 8 µg/ml. Two of the isolates were available for molecular analysis. Pulse field gel electrophoresis identified them as belonging to one cluster.

Conclusions: To our knowledge, this is the first reported outbreak of carbapenem-resistant A. baumannii in a NICU.  We report our experience to underscore the lack of information on safe and effective treatment options for neonates with multi-drug-resistant A.baumannii and to highlight infection control practices in the pod-style NICU setting, as compared to single or double room units.