ENZYME-LINKED-IMMUNOSORBENT-ASSAY FOR DETECTION OF IMMUNOGLOBULIN-G ANTIBODIES TO ESCHERICHIA-COLI VERO CYTOTOXIN-1

The frequency of Vero cytotoxin 1 (VT1)-neutralizing antibody (NAb) in serum specimens from 790 age-stratified (0 to 70 years) control indiv iduals from Toronto was 61 of 790 (7.7%), with a peak of 19% in the 20 - to 30-year-old age group and a second peak of 16.7% in the 60- to 70 -year-old age group. A total of 568 serum specimens, including 538 fro m the 790 Toronto control subjects, 21 from patients from three outbre aks of VT-producing Escherichia coli (VTEC) infection, and 9 known VT1 -NAb-positive serum specimens from patients,vith hemolytic-uremic synd rome (HUS), were then tested for the presence of anti-VT1 immunoglobul in G (IgG) by an enzyme-linked immunosorbent assay (ELISA). The mean E LISA values of 522 VT1-NAb-negative serum specimens and 46 VT1-NAb-pos itive serum Specimens were 0.09 +/- 0.06 (range, 0 to 0.56) and 0.78 /- 0.66 (range, 0.16 to 2.91), respectively (P < 0.001; Student's t te st). With a breakpoint of 0.21 (mean ELISA value of the VT1-NAb-negati ve sera + 2 standard deviations), the sensitivity, specificity, positi ve predictive value, and negative predictive value of the VT1 IgG ELIS A compared with those of the VT1-NAb assay were, respectively, 95.7, 9 8.7, 86.3, and 99.6%. There were nine discrepant serum specimens, of w hich seven were anti-VT1 IgG positive and VT1-NAb negative and two wer e anti-VT1 IgG negative and VT1-NAb positive. The ELISA was also used for testing 238 control serum specimens from The Netherlands, Japan, a nd India and acute- and convalescent-phase serum specimens from 42 Tor onto patients with HUS. The frequencies of anti-VT1 IgG (with VT1-NAb frequencies in parentheses) in control sera from The Netherlands, Japa n, and India were 6% (3%), 1.1% (0%), and 12% (10%), respectively, wit h no age clustering. The frequencies of anti-VT1 IgG seropositivity in HUS patients were 5 of 14(35.7%) in patients with unknown toxin expos ure, 2 of 22 (9.1%) in individuals with known exposure to VT1 plus VT2 or VT1 alone, and 0 of 6 (0%) in patients exposed to only VT2. Develo pment of a serum anti-VT1 IgG response appears to be the exception rat her than the rule in sporadic HUS patients infected with VTEC expressi ng VT1. However, in two family outbreaks associated with VTEC strains expressing VT1 alone and VT1 plus VT2, respectively, the presence of a nti-VT1 IgG in virtually all. exposed individuals who remained symptom free suggests that the presence of antibody,vas associated with prote ction.