Detection of serum and faecal antibodies in haemorrhagic colitis caused by Escherichia coli O157.

Cases of culture-confirmed clinically typical haemorrhagic colitis caused by verocytotoxin-producing (VT+) Escherichia coli O157 and age- and sex-matched control patients were examined for antibodies to E. coli O157. Serum samples from 28 cases and 34 patients in control group 1 were examined for VT1- and VT2-neutralising antibodies, E. coli O157 agglutinating antibodies, and by an enzyme immunoassay (EIA) technique for IgG antibodies against smooth lipopolysaccharide purified from E. coli O157 and for IgG antibodies against whole intact E. coli O157 cells. Differences between antibody titres were significant when compared by a Wilcoxon two-sample test for E. coli O157 agglutinating antibodies (p < 0.05) and IgG antibodies against whole cells (p < 0.001). The whole-cell EIA was used further to examine faecal samples from 93 cases and 47 patients in control group 2 for IgA antibodies. Elevated levels of faecal IgA specific for E. coli O157 were found in 59 (63.4%) of 93 cases but in only 10 (21.2%) of 47 control patients (p < 0.001); follow-up faecal samples from five cases all showed marked rises in levels of IgA that appeared to coincide with cessation of excretion of the organism. Detection of specific faecal IgA with a whole-cell EIA, although requiring further evaluation, may be a useful addition to tests currently available for the diagnosis of infection by VT+ E. coli O157.