Diarrheagenic Escherichia coli in sub-Saharan Africa: status, uncertainties and necessities

Diarrhea is a leading cause of illness and death, particularly in developing countries. Enteropathogenic Escherichia coli, enterotoxigenic E. coli (ETEC), enteroinvasive E. coli, enterohemorrhaghic E. coli (EHEC), enteroaggregative E. coli (EAEC) and diffusely adherent E. coli (DAEC) have been associated with diarrheal disease in different parts of Africa, particularly among young children, HIV-positive individuals, and visitors from abroad. Each of these E. coli pathotypes uses distinct mechanisms, which are only partially understood, to colonize infected hosts and produce diarrhea. All known diarrheagenic E. coli pathotypes have been reported from diverse locations within Africa but the true burden from these pathogens is unknown because very few studies seeking these organisms with discriminatory methodology have been performed. Recent reports implicate ETEC and EAEC in a considerable proportion of childhood and travellers' diarrheas and suggest that some sub-types of these categories may have greater epidemiological significance than others. The significant contribution of EHEC to bloody diarrhea and hemolytic uremic syndrome is underappreciated because diagnostic capacity for this pathotype is generally inferior to that for confounders such as Shigella and Entamoeba. Recent studies in Africa have revealed the worrisome emergence of antimicrobial resistance and high asymptomatic carriage rates for diarrheagenic E. coli but bacterial and host factors that predispose to disease, as well as non-human reservoirs, are largely unknown. Future diarrheal disease research needs to focus on broadening the repertoire of pathogens sought in epidemiological surveys to include multiple categories of diarrheagenic E. coli while building capacity to detect these pathogens in local reference laboratories.