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. 2013 Jul;57(1):65-76.
doi: 10.1093/cid/cit192. Epub 2013 Apr 2.

Clustering of antimicrobial resistance outbreaks across bacterial species in the intensive care unit

Anne L M Vlek  1 , Ben S Cooper, Theodore Kypraios, Andy Cox, Jonathan D Edgeworth, Olga Tosas Auguet
Affiliations

Clustering of antimicrobial resistance outbreaks across bacterial species in the intensive care unit

Anne L M Vlek et al. Clin Infect Dis. 2013 Jul.

Abstract

Background: There are frequent reports of intensive care unit (ICU) outbreaks due to transmission of particular antibiotic-resistant bacteria. Less is known about the burden of outbreaks of resistance due to horizontal transfer of mobile genetic elements between species. Moreover, the potential of existing statistical software as a preliminary means for detecting such events has never been assessed. This study uses a software package to determine the burden of species and resistance outbreaks in 2 adjacent ICUs and to look for evidence of clustering of resistance outbreaks consistent with interspecies transmission of resistance elements.

Methods: A retrospective analysis of data from 2 adjacent 15-bed adult ICUs between 2002 and 2009 was undertaken. Detection of bacterial species-groups and resistance outbreaks was conducted using SaTScan and WHONet-SaTScan software. Resampling and permutation methods were applied to investigate temporal clustering of outbreaks.

Results: Outbreaks occurred for 69% of bacterial species-groups (18/26), and resistance outbreaks were detected against 63% of antibiotics (10/16). Resistance outbreaks against 7 of 10 antibiotics were observed in multiple species-groups simultaneously and there was evidence of inter-species-group dependence for 4 of 7 antibiotics; background temporal changes in resistance did not explain the temporal aggregation of outbreaks in 3 of 7 antibiotics.

Conclusions: Species outbreaks occurred for the majority of bacteria commonly identified in the ICU. There was evidence for frequent temporal clustering of resistance outbreaks consistent with interspecies transmission of resistance elements. Wider application of outbreak detection software combined with targeted sequencing of bacterial genomes is needed to understand the contribution of interspecies gene transfer to resistance emergence.

Keywords: antibiotic resistance; intensive care unit; outbreaks.

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Figures

Figure 1.
Figure 1.
Incidence of identification of species-groups from patient clinical samples in 2 adjacent intensive care units (ICUs). Detected outbreaks after temporal adjustment for underlying temporal trends are depicted in blue. Red lines show outbreaks that would have been detected if no temporal adjustment had been applied. The number of patient-days for each ICU is shown at top.
Figure 2.
Figure 2.
Number of patient-days of antibiotic therapy in 2 adjacent intensive care units for different antimicrobial agents. Colored bars represent detected outbreaks of antibiotic resistance. Abbreviation: ICU, intensive care unit; Pip/Taz, piperacillin/tazobactam.
See this image and copyright information in PMC

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