Geogenomic Segregation and Temporal Trends of Human Pathogenic Escherichia coli O157:H7, Washington, USA, 2005-20141.

Gillian A.M Tarr,Amanda I Phipps,Jon Wakefield,Thomas E Besser,Smriti Shringi,Hanna N Oltean,Phillip I Tarr,Jonathan Mayer,Peter Rabinowitz

doi:10.3201/eid2401.170851

Abstract

The often-noted and persistent increased incidence of Escherichia coli O157:H7 infections in rural areas is not well understood. We used a cohort of E. coli O157:H7 cases reported in Washington, USA, during 2005–2014, along with phylogenomic characterization of the infecting isolates, to identify geographic segregation of and temporal trends in specific phylogenetic lineages of E. coli O157:H7. Kernel estimation and generalized additive models demonstrated that pathogen lineages were spatially segregated during the period of analysis and identified a focus of segregation spanning multiple, predominantly rural, counties for each of the main clinical lineages, Ib, IIa, and IIb. These results suggest the existence of local reservoirs from which humans are infected. We also noted a secular increase in the proportion of lineage IIa and IIb isolates. Spatial segregation by phylogenetic lineage offers the potential to identify local reservoirs and intervene to prevent continued transmission.

Highlights

The often-noted and persistent increased incidence of Escherichia coli O157:H7 infections in rural areas is not well understood
During the study period, 1,160 E. coli O157:H7 cases were reported to Department of Health (DOH)
33 isolates, representing 31 pulsed-field gel electrophoresis (PFGE) types, were not available for typing, and isolates from 6 cases were excluded as biochemically atypical E. coli O157:H7

Summary

Introduction

The often-noted and persistent increased incidence of Escherichia coli O157:H7 infections in rural areas is not well understood. We used a cohort of E. coli O157:H7 cases reported in Washington, USA, during 2005–2014, along with phylogenomic characterization of the infecting isolates, to identify geographic segregation of and temporal trends in specific phylogenetic lineages of E. coli O157:H7. Spatial segregation by phylogenetic lineage offers the potential to identify local reservoirs and intervene to prevent continued transmission. Many reported infections are attributed to food vehicles [1], but studies have implicated other risk factors, and environmental transmission may be notable in rural areas [3,4,5,6,7]. Residing in a rural area confers increased risk for E. coli O157:H7 infection [9,10].

Methods

Results

Conclusion