Research Article: Diarrheagenic Escherichia coli Carrying Supplementary Virulence Genes Are an Important Cause of Moderate to Severe Diarrhoeal Disease in Mexico

Date Published: March 4, 2015

Publisher: Public Library of Science

Author(s): Sandra Patzi-Vargas, Mussaret Bano Zaidi, Iza Perez-Martinez, Magda León–Cen, Alba Michel-Ayala, Damien Chaussabel, Teresa Estrada-Garcia, Mathieu Picardeau.

Abstract: Diarrheagenic Escherichia coli (DEC) cause acute and persistent diarrhoea worldwide, but little is known about their epidemiology in Mexico. We determined the prevalence of bacterial enteropathogens in 831 children with acute diarrhoea over a four-year period in Yucatan, Mexico. Six DEC supplementary virulence genes (SVG), mainly associated with enteroaggregative E. coli (EAEC), were sought in 3100 E. coli isolates. DEC was the most common bacterial enteropathogen (28%), surpassing Salmonella (12%) and Shigella (9%). Predominant DEC groups were diffusely adherent E. coli (DAEC) (35%), EAEC (24%), and enteropathogenic E. coli (EPEC) (19%). Among children with DEC infections, 14% had severe illness mainly caused by EPEC (26%) and DAEC (18%); 30% had moderate diarrhoea mainly caused by DAEC (36%), mixed DEC infections (33%) and EAEC (32%). DAEC was most prevalent during spring, while ETEC, EAEC and EPEC predominated in summer. EAEC was more frequent in children 6–24 months old than in those younger than 6 months of age (P = 0.008, OR = 4.2, 95% CI, 1.3–13.9). The presence of SVG dispersin, (aatA), dispersin-translocator (aatA), enteroaggregative heat-stable toxin 1 (astA), plasmid encoded toxin (pet), cytolethal distending toxin (cdt) was higher in DEC than non-DEC strains, (36% vs 26%, P <0.0001, OR = 1.5, 95% CI, 1.3–1.8). 98% of EAEC-infected children harboured strains with SVG; 85% carried the aap-aatA gene combination, and 33% of these also carried astA. 28% of both EPEC and ETEC, and 6% of DAEC patients had strains with SVG. 54% of EPEC patients carried pet-positive strains alone or in combination with astA; only this DEC group harboured cdt-positive isolates. All ETEC patients carried astA- or astA-aap-positive strains. astA and aap were the most common SVG in DAEC (3% and 2%) and non-DEC strains (21% and 13%). DEC carrying SVG are an important cause of moderate to severe bacterial diarrhoea in Mexican children.

Partial Text: Diarrhoeal illness is a major cause of mortality and morbidity among children less than 5 years of age accounting for 711,800 deaths and 1.731 billion cases, with an incidence of 2.7 diarrhoeal episodes per child per year in 2011 [1]. In Mexico, diarrhoeal illness continues to be a national health problem [2,3]. It is the second cause of morbidity and the fifth cause of mortality among children under five years of age. In 2010, more than 5.5 million diarrhoeal cases were reported for a national rate of 5,264.24 per 100,000 inhabitants; most of these cases occur in young children [2,3]. The burden is particularly high in the state of Yucatan, which occupies third place in diarrhoea-associated mortality nationwide [3].

Despite the plethora of scientific reports on diarrheal disease in children under five years of age, this study is one of the few to include the identification of routine bacterial pathogens and all six DEC groups by molecular methods in a hospital setting over a four year period. In our active surveillance study that included children with acute diarrhoea in Yucatan, bacterial pathogens were found in a higher proportion (56%) of patients than in other tropical regions [9,44]. Recent studies on diarrheal disease conducted at Paediatric hospitals in Brazil [9] and Burkina Faso [44], for example, reported a prevalence of bacterial pathogens of 42% and 40%, respectively. This contrasts with a 26% prevalence reported at a Paediatric Emergency Department in Cincinnati [5]. A common denominator in all these studies was that DEC, as a group, was the most frequently identified bacterial pathogen in children with diarrhoea. Possible explanations for these geographic differences include variations in socioeconomic conditions, laboratory infrastructure and climate. Our study found strong seasonal patterns for almost all DEC-groups. DAEC was highly prevalent during the hot, dry months, while ETEC, EAEC and EPEC were most frequent during the rainy season, which s with other studies conducted in Mexico [21,45].



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