title: Prevalence, virulence profiles, and clinical significance of Shiga toxin-negative variants of enterohemorrhagic Escherichia coli O157 infection in humans.
abstract: BACKGROUND
  Escherichia coli O157, of the H7 clone, exists in humans and in the environment as Shiga toxin (Stx)-positive and Stx-negative variants. Stx production by infecting organisms is considered to be a critical requirement for the development of hemolytic uremic syndrome (HUS), which occurs in approximately 15% of E. coli O157-infected patients. It is unknown if loss of the stx gene during the early stage of an enterohemorrhagic E. coli infection prevents HUS, or if absence of the stx gene from E. coli O157 reduces or ablates virulence.
  
  
  METHODS
  We determined the frequency of stx-positive and stx-negative E. coli O157 isolates in stool samples obtained from patients who experienced sporadic cases of diarrhea or HUS, as well as the frequency in samples obtained during outbreaks, and investigated the clinical course of the disease.
  
  
  RESULTS
  Among E. coli O157 isolates obtained from samples related to sporadic cases of diarrhea, stx-negative strains accounted for 4%. The proportion of stx-negative strains was significantly higher among sorbitol-fermenting, nonmotile E. coli O157 isolates (12.7%) than among non-sorbitol-fermenting E. coli O157:H7 or nonmotile isolates (0.8%; P<.001). stx-Negative sorbitol-fermenting E. coli O157 isolates were also observed in samples related to 3 HUS outbreaks and 1 outbreak of diarrhea caused by sorbitol-fermenting, nonmotile enterohemorrhagic E. coli O157; additionally, they were the only pathogens that were isolated in 2 other outbreaks of diarrhea without HUS.
  
  
  CONCLUSIONS
  Strains of stx-negative E. coli O157 isolated from stool samples of patients are either inherently stx-negative strains that cause mostly uncomplicated diarrhea, or strains that descended from enterohemorrhagic E. coli O157 by the loss of the stx gene during infection; the latter strains may still cause severe disease.
authors.affiliation: National Consulting Laboratory on Hemolytic Uremic Syndrome, Institute for Hygiene, University of Münster, Münster, Germany.
authors.forename: Alexander W
authors.initials: AW
authors.lastname: Friedrich
authors.forename: Wenlan
authors.initials: W
authors.lastname: Zhang
authors.forename: Martina
authors.initials: M
authors.lastname: Bielaszewska
authors.forename: Alexander
authors.initials: A
authors.lastname: Mellmann
authors.forename: Robin
authors.initials: R
authors.lastname: Köck
authors.forename: Angelika
authors.initials: A
authors.lastname: Fruth
authors.forename: Helmut
authors.initials: H
authors.lastname: Tschäpe
authors.forename: Helge
authors.initials: H
authors.lastname: Karch
mesh_terms: D001427:Bacterial Toxins / Q000378:metabolism; D003967:Diarrhea / Q000209:etiology / Q000382:microbiology; D004196:Disease Outbreaks; D004927:Escherichia coli Infections / Q000453:epidemiology* / Q000378:metabolism; D019453:Escherichia coli O157 / Q000737:chemistry / Q000472:pathogenicity*; D005243:Feces / Q000382:microbiology; D006463:Hemolytic-Uremic Syndrome / Q000209:etiology*; D006801:Humans; D015995:Prevalence; D022621:Shiga Toxin / Q000032:analysis*; D014774:Virulence
chemical_list: D001427:Bacterial Toxins; D022621:Shiga Toxin