IMPACT OF FREE VEROTOXIN TESTING ON EPIDEMIOLOGY OF DIARRHEA CAUSED BY VEROTOXIN-PRODUCING ESCHERICHIA-COLI

During a 10-week period in the summer of 1990, an epidemiologic invest igation of the prevalence of verotoxin (VT)-producing Escherichia coli infection was conducted in Calgary, Alberta, Canada. Consecutive stoo l specimens (n = 3,577) were cultured for E. coli O157:H7, and fecal f iltrates were tested for free VTs (FVTs). E. coli O157:H7 was recovere d from 22 specimens (0.6%), but VT was detected in 74 specimens (2.1%) . Sixty-nine stool specimens positive for FVTs or E. coli O157:H7 were probed for VT genes by colony blot hybridization; 22 of 38 VT gene pr obe-positive isolates were non-O157:H7 E. coli organisms. Fourteen of 22 strains could not be induced to produce VT in vitro, despite the pr esence of FVTs in the stool sample, positivity on colony blot hybridiz ation, positive PCR probes with the primers described by Pollard et al . (D. R. Pollard, W. R4. Johnson, H. Lier, S. D. Tyler, and K. R. Roze e, J. Clin. Microbiol. 28:540-545, 1990) or Gannon ct al. (V. P. Ganno n, R. K. King, J. Y. Kim, and E. J. Golsteyn-Thomas, Appl. Environ. Mi crobiol. 58:3809-3815, 1992) (but not those described by Kaich and Mey er [11. Rarch and T. Meyer, J. Clin. Microbiol. 27:2751-2757, 1989]), and positive Southern blot analysis of isolates in 10 of 14 strains. T he patient survey questionnaire showed that E. coli O157:H7 infection was associated with bloody diarrhea of short duration, whereas infecti on with other serotypes or persistence of PVT only was associated with longer-duration nonbloody diarrheal illness. We conclude that (i) det ection of FVT in stools enhances the diagnosis of VT infection threefo ld over cultures for E. coli O157:H7, (ii) cultures for E. coli O157:H 7 detect the majority of organisms of that serotype, (iii) the spectru m of disease produced by organisms of non-O157:H7 serotypes may includ e less severe but more protracted illness, and (iv) differences in the in vive and in vitro expression of toxin and results of genetic probe studies highlight the need to examine control mechanisms of toxin pro duction.