additional studies, but factors other than bacterial virulence are probably more important in the development of a symptomatic UTI into USB.

1. McBean M, Rajamani S. Increasing rates of hospitalizationdue to septicemia in the US elderly population, 1986–97.J Infect Dis 2001; 183: 596–603.2. Johnson JR, Kuskowski MA, O’Bryan TT, Maslow JN.Epidemiological correlates of virulence genotype andphylogenetic background among Escherichia coli bloodisolates from adults with diverse-source bacteremia.J Infect Dis 2002; 185: 1439–1447.3. Johnson JR. Virulence factors in Escherichia coli urinarytract infection. Clin Microbiol Rev 1991; 4: 80–128.4. Johnson JR, Stell AL. Extended virulence genotypes ofEscherichia coli strains from patients with urosepsis inrelation to phylogeny and host compromise. J Infect Dis2000; 181: 261–272.5. Herzer PJ, Inouye S, Inouye M, Whittam TS. Phylogeneticdistribution of branched RNA-linked multicopy single-stranded DNA among natural isolates of Escherichia coli.J Bacteriol 1990; 172: 6175–6181.6. Duriez P, Clermont O, Bonacorsi S et al. CommensalEscherichia coli isolates are phylogenetically distributedamong geographically distinct human populations.Microbiology 2001; 147: 1671–1676.7. Clermont O, Bonacorsi S, Bingen E. Rapid and simpledetermination of the Escherichia coli phylogenetic group.Appl Environ Microbiol 2000; 66: 4555–4558.8. Yamamoto S, Terai A, Yuri K, Kurazono H, Takeda Y,Yoshida O. Detection of urovirulence factors in Escherichiacoli by multiplex polymerase chain reaction. FEMS Immu-nol Med Microbiol 1995; 12: 85–90.9. Bonacorsi S, Houdouin V, Mariani-Kurkdjian P,Mahjoub-Messai F, Bingen E. Comparative prevalence ofvirulence factors in Escherichia coli causing urinary tractinfection in male infants with and without bacteremia.J Clin Microbiol 2006; 44: 1156–1158.10. Moreno E, Planells I, Prats G, Planes AM, Moreno G,Andreu A. Comparative study of Escherichia coli virulencedeterminants in strains causing urinary tract bacteremiaversus strains causing pyelonephritis and other sources ofbacteremia. Diagn Microbiol Infect Dis 2005; 53: 93–99.11. Jantunen ME, Saxen H, Lukinmaa S, Ala-Houhala M,Siitonen A. Genomic identity of pyelonephritogenicEscherichia coli isolated from blood, urine and faeces ofchildren with urosepsis. J Med Microbiol 2001; 50: 650–652.12. Karkkainen UM, Kauppinen J, Ikaheimo R, Katila ML.Random amplified polymorphic DNA (RAPD) analysis ofEscherichia coli strains: comparison of urinary and con-comitant blood isolates of urosepsis patients. APMIS 1996;104: 437–443.13. Benton J, Chawla J, Parry S, Stickler D. Virulence factors inEscherichia coli from urinary tract infections in patientswith spinal injuries. J Hosp Infect 1992; 22: 117–127.14. Johnson JR, Owens K, Gajewski A, Kuskowski MA. Bac-terial characteristics in relation to clinical source ofEscherichia coli isolates from women with acute cystitis orpyelonephritis and uninfected women. J Clin Microbiol2005; 43: 6064–6072.15. Johnson JR, Russo TA. Molecular epidemiology of extra-intestinal pathogenic (uropathogenic) Escherichia coli. Int JMed Microbiol 2005; 295: 383–404.