Rhizobium radiobacter, an environmental Gram-negative bacterium, can occasionally cause infection in humans. Between November 29 and December 7, 2015, our hospitals microbiology laboratory reported two cases of R. radiobacter bacteremia admitted to the cardiology department, which triggered an outbreak investigation.
We generated a line list to identify possible common sources for the bacteremia that both patients were exposed to, followed by on-site audits and environmental swabs. Blood culture isolates were identified by MALDI-TOF mass-spectrometry (MS) and 16S-rDNA analyses. Relatedness of the two outbreak isolates (A, B) and two independent control R. radiobacter isolates (B, C) was determined by MALDI-TOF MS based typing via visual examination of the peak profiles and principal components analysis (PCA). We used pulsed-field gel electrophoresis (PFGE) to confirm the relatedness of the isolates.
Case 1 was a 72 year-old male admitted for an elective transcatheter aortic valve implantation. Case 2 was an 83 year-old female admitted because of congestive heart failure. Based on the line list the patients shared two locations: the cardiac catheterization laboratory A and the radiology room 1. The timeline is shown in Figure 1. Audits revealed no breaches of infection prevention precautions by the involved healthcare personnel. We suspected the contrast injector pump mechanism used in laboratory A (a semi-open system) to pose an infection risk, however, the pump was not found to be contaminated. Ongoing construction works in the adjacent room may have been the source of transient contamination. MALDI-TOF MS recorded differences in 58 peaks (m/z range of 2 10 kDa) of the four strains. The mass spectra of isolates A and B showed no difference . The PCA dendrogram indicated close relatedness of the two isolates, which was confirmed by PFGE (Figure 2).
We report a self-limited outbreak with two cases of R. radiobacter bloodstream infections likely to originate from a common source. Partly open systems destined to be sterile - such as the contrast injector pump - represent an infection risk. Here, we highlight the successful use of MALDI-TOF MS as a potential tool for outbreak analysis.
E. Lo Priore,
A. Egli, None
W. Steiger, None
M. Laguardia, None
S. Droz, None
J. Marschall, None
R. Sommerstein, None