This case-control study detected and characterized Shigella and diarrheagenic Escherichia coli (DEC) types among Vietnamese children less than 5 years old. In 249 children with diarrhea and 124 controls, Shigella spp. was an important cause of diarrhea (P < 0.05). We used multiplex PCR and DNA probes to detect enteroinvasive E. coli (EIEC), enteroaggregative E. coli (EAggEC), enteropathogenic E. coli (EPEC), attaching and effacing E. coli (A/EEC), verocytotoxin-producing E. coli (VTEC), and enterotoxigenic E. coli (ETEC). The prevalences of DEC in the diarrhea and control groups were 25.7 and 10.5%, respectively. In 62 children with diarrhea, 64 DEC strains included 22 EAggEC (8.8%), 2 EIEC (0.8%), 23 A/EEC (9.2%), 7 EPEC (2.8%), and 10 ETEC strains (4.0%). Among controls, 13 DEC strains included 5 EAggEC strains (4.0%), 7 A/EEC strains (5.6%), and 1 EPEC strain. The characterization of DEC by serotypes, antimicrobial susceptibility patterns, virulence genes, and pulsed-field gel electrophoresis showed the occurrence of many different and highly heterogenic DEC subtypes, but common serotypes were found among ETEC, EIEC and EPEC, respectively. Serotyping was used to distinguish between A/EEC and EPEC. However, A/EEC, EPEC, and EAggEC were isolated at high frequency from both cases and controls. Further in-depth studies are needed to better understand important virulence factors of DEC, especially A/EEC, EPEC, and EAggEC.

We prospectively studied diarrhoea incidence among 1655 children < 5 years of age in northern Vietnam for 1 year using primarily passive surveillance. Standard culture methods were used to detect bacterial pathogens. Overall 2160 cases occurred (1·3 cases/child per year). Peak rates of diarrhoea occurred in children < 12 months old. Rates ranged from 3·3 cases/child per year in children < 1 year old, to 0·7 cases/child per year in 4-year-olds. Campylobacter, shigella and enterotoxigenic Escherichia coli were most commonly isolated. Rates detected by active surveillance were about twice those detected passively. S. flexneri was the most common shigella serogroup (65%). S. flexneri serotypes 6, 4, 1 and Y were most common, but 40% were untypable using commercial antisera. The data illustrate important regional differences in pathogen prevalence and shigella serotype distribution. Shigella vaccine development strategies, commonly targeting S. flexneri 2a, S. sonnei and S. dysenteriae 1, will have little impact on diarrhoea rates in Vietnam.

A case-control study was conducted to identify the aetiology of diarrhoeal diseases in pre-school children in a suburban area of Hanoi where the use of untreated wastewater in agriculture and aquaculture is a common practice. Stool specimens and clinical information were collected from 111 pairs of children with diarrhoea and healthy controls. A total of 73 cases (66 %) and 41 controls (36 %) had an enteric pathogen. The pathogens most often associated with diarrhoea were rotavirus (17 % of cases) and Entamoeba histolytica (15 %), followed by Shigella (5 %). Diarrhoeagenic Escherichia coli (DEC) was found in 23 % of both patients and controls. Characterization of DEC by serotyping, antimicrobial susceptibility test and PFGE showed that DEC represented by different pathotypes belonged to various serotypes. Except for three enterotoxigenic E. coli strains, typing by PFGE revealed no correlation between pathotype and serotype of DEC strains. This suggests a high prevalence of a variety of DEC subtypes in this area. For this particular region, vaccine development strategies targeting rotavirus and Shigella are likely to be of public health benefit, whereas the role of DEC and preventive measures need to be further elaborated. INTRODUCTIONDiarrhoeal disease is a major problem throughout the world, and is responsible for high morbidity and mortality among children, especially in developing countries. Some aetiological studies of diarrhoeal diseases have been carried out in Vietnam (Isenbarger et al., 2001;Nguyen et al., 2005a), but not in areas where untreated wastewater is used in agriculture and aquaculture. The association of wastewater use and risks to human health has been assessed in various countries such as Israel, Morocco, Mexico and Pakistan, where wastewater is also commonly used for irrigation (Shuval et al., 1989;Feenstra et al., 2000;Habbari et al., 2000; Blumenthal et al., 2001; WHO, 2006). Some studies have highlighted a high risk of being infected with intestinal parasites and of getting diarrhoeal diseases, especially in small children who live in the wastewaterusing areas (Cifuentes, 1998;Cifuentes et al., 2000).In a hospital study, the prevalences of diarrhoeagenic Escherichia coli (DEC) were 22.5 and 12 % in the diarrhoea and control groups, respectively, but mainly due to a high frequency of enteroaggregative E. coli (EAggEC) (Nguyen et al., 2005a). Using dot-blot hybridization in another hospital-based study, eae-positive E. coli were found at a significantly higher prevalence in children with diarrhoea than in asymptomatic controls (Bodhidatta et al., 2007). In a study outside Hanoi, Campylobacter and Shigella were found to be associated with diarrhoea, and enterotoxigenic E. coli (ETEC) was the prevalent group of DEC (Isenbarger et al., 2001). None of these studies included detailed characterization of DEC.The aim of the present study was to determine the aetiology of diarrhoeal diseases in children from families engaged in Abbreviations: A/EEC, attaching and effacing Escherichia coli; DEC, di...