Changes in serotypes of enterotoxigenic Escherichia coli in Dhaka over time: usefulness of polyvalent antisera

The finding that enterotoxigenic (ET) Escherichia coli strains from many geographic areas belong to a limited number of serogroups led investigators to hope that polyvalent antisera could be used to screen for ET E. coli in areas of the world where more complicated tests of toxigenicity are not available. We compared the serotypes of 207 ET E. coli strains obtained from patients attending the Dhaka Hospital of the International Centre for Diarrhoeal Disease Research, Bangladesh, in 1980 with results obtained from similar surveys conducted in 1976 and 1978. During that time the distribution of serogroups changed significantly so that only 46% of our strains had O serogroups included in the polyvalent antisera capable of detecting 66% of ET E. coli strains in 1978. O167, a serogroup which was not included previously, was the third most common serogroup in our study. These findings suggest that polyvalent antisera used to screen for ET E. coli need to be reassessed over time as well as in different geographic areas and may not be as useful for field diagnosis as was originally hoped.