Enteroinvasive Escherichia coli May Account for Uncultured Shigella

A recent article by Lindsay and others 1 reported that stool quantitative polymerase chain reaction (qPCR), with a 14,000 copy number cutoff, identified more cases of Shigella infection than conventional and widely used culture methods. The authors suggested that there may be a significant underestimation of the contribution of Shigella to diarrheal disease because of the limits of culture and have made a similar claim in a previous but smaller study. As some of the authors remarked in a previous article, enteroinvasive Escherichia coli (EIEC) strains also possess ipaH. 2 Indeed, this target is applied for both Shigella and EIEC when the two pathotypes are not delineated. It is therefore possible, or indeed probable, that the qPCR methodology has uncovered a hidden burden due to EIEC rather than-or with-missed Shigella cases.