Occupational transmission of Acinetobacter baumannii from a United States serviceman wounded in Iraq to a health care worker

Abstract

Background: Acinetobacter baumannii is increasingly recognized as being a significant pathogen associated with nosocomial outbreaks in both civilian and military treatment facilities. Current analyses of these outbreaks frequently describe patient-to-patient transmission. To date, occupational transmission of A. baumannii from a patient to a health care worker (HCW) has not been reported. We initiated an investigation of an HCW with a complicated case of A. baumannii pneumonia to determine whether a link existed between her illness and A. baumannii-infected patients in a military treatment facility who had been entrusted to her care.

Methods: Pulsed-field gel electrophoresis and polymerase chain reaction/electrospray ionization mass spectrometry, a form of multilocus sequencing typing, were done to determine clonality. To further characterize the isolates, we performed a genetic analysis of resistance determinants.

Results and conclusions: A "look-back" analysis revealed that the multidrug resistant A. baumannii recovered from the HCW and from a patient in her care were indistinguishable by pulsed-field gel electrophoresis. In addition, polymerase chain reaction/electrospray ionization mass spectrometry indicated that the isolates were similar to strains of A. baumannii derived from European clone type II (Walter Reed Army Medical Center strain type 11). The exposure of the HCW to the index patient lasted for only 30 min and involved endotracheal suctioning without use of an HCW mask. An examination of 90 A. baumannii isolates collected during this investigation showed that 2 major and multiple minor clone types were present and that the isolates from the HCW and from the index patient were the most prevalent clone type. Occupational transmission likely occurred in the hospital; HCWs caring for patients infected with A. baumannii should be aware of this potential mode of infection spread.

Figure 1

Days on which the health care worker provided direct care to 5 different National Naval Medical Center patients colonized or infected with Acinetobacter baumannii. Above each arrow is the designated PFGE lane shown in figure 2 that corresponds to the A. baumannii clonal types recovered from these patients.

Figure 2

PFGE analysis of the Acinetobacter baumanii isolate recovered from the health care worker, compared with A. baumannii patient isolates from the National Naval Medical Center. Lanes 1 and 8 are molecular weight standards. Lanes 4 and 7 represent the genomic digests of the isolates from the health care worker (lane 4) and the wounded US serviceman (lane 7). Lanes 2, 3, 5, and 6 are genomic digests of A. baumannii isolated from patients under the direct care of the health care worker and represent additional clone types circulating at the National Naval Medical Center.

Figure 3

PFGE analysis of 90 patient isolates of A. baumannii collected from March 2006 to November 2006.

Figure 4

Flow diagram representing the dissemination of different clone types identified at the National Naval Medical Center (NNMC). The isolates from the US serviceman and the HCW are added to clone type I to arrive at 31 total isolates. OIF, Operation Iraqi Freedom; WRAMC, Walter Reed Army Medical Center.