Multicenter Outbreak of Gram-Negative Bloodstream Infections in Hemodialysis Patients

Abstract

Rationale & objective: Contaminated water and other fluids are increasingly recognized to be associated with health care-associated infections. We investigated an outbreak of Gram-negative bloodstream infections at 3 outpatient hemodialysis facilities.

Study design: Matched case-control investigations.

Setting & participants: Patients who received hemodialysis at Facility A, B, or C from July 2015 to November 2016.

Exposures: Infection control practices, sources of water, dialyzer reuse, injection medication handling, dialysis circuit priming, water and dialysate test findings, environmental reservoirs such as wall boxes, vascular access care practices, pulsed-field gel electrophoresis, and whole-genome sequencing of bacterial isolates.

Outcomes: Cases were defined by a positive blood culture for any Gram-negative bacteria drawn July 1, 2015 to November 30, 2016 from a patient who had received hemodialysis at Facility A, B, or C.

Analytical approach: Exposures in cases and controls were compared using matched univariate conditional logistic regression.

Results: 58 cases of Gram-negative bloodstream infection occurred; 48 (83%) required hospitalization. The predominant organisms were Serratia marcescens (n=21) and Pseudomonas aeruginosa (n=12). Compared with controls, cases had higher odds of using a central venous catheter for dialysis (matched odds ratio, 54.32; lower bound of the 95% CI, 12.19). Facility staff reported pooling and regurgitation of waste fluid at recessed wall boxes that house connections for dialysate components and the effluent drain within dialysis treatment stations. Environmental samples yielded S marcescens and P aeruginosa from wall boxes. S marcescens isolated from wall boxes and case-patients from the same facilities were closely related by pulsed-field gel electrophoresis and whole-genome sequencing. We identified opportunities for health care workers' hands to contaminate central venous catheters with contaminated fluid from the wall boxes.

Limitations: Limited patient isolates for testing, on-site investigation occurred after peak of infections.

Conclusions: This large outbreak was linked to wall boxes, a previously undescribed source of contaminated fluid and biofilms in the immediate patient care environment.

Keywords: Gram-negative bacteria; Hemodialysis; bacterial contamination; biofilm; bloodstream infection (BSI); central venous catheter; contamination; cross infection; dialysis facility; disinfection; environmental sampling; healthcare-associated infection (HAI); infection prevention; modifiable risk factor; outbreak; patient safety.

Figure 1.

Dialysis station wall boxes with bicarbonate, acid, reverse osmosis water, and waste connections and lines labeled.

Figure 2.

Epidemic curve of Gram-negative bloodstream infections in hemodialysis patients at Facilities A, B, and C (n = 64). Solid box indicates investigation period from July 2015 to November 2016; n = 58. Dashed arrows indicate date reuse of dialyzers ceased at each facility.

Figure 3.

Phylogenetic trees of reference-based single-nucleotide polymorphism (SNP) analysis comparing Serratia marcescens case-patient and wall box isolates from 3 different outpatient hemodialysis facilities (A, B, and C; SNPs from core genome size of 29.87%). The phylogenetic tree represents genetic distances based on branch length; that is, isolates A2 and A3 (which have short branches between one another) are closely related to one another and more distantly related to isolates A1 and A4; *C3 and C4 were found to be indistinguishable using pulsed-field gel electrophoresis. Core genome size of isolates for individual facility whole genome sequencing comparisons are as follows: Facility A, 46.47%; Facility B, 78.46%; Facility C, 85.94%. The sequence reads generated as part of this study are available at National Center for Biotechnology Information BioProject ID PRJNA454492.