**7.1 An overview of DAEC**

Diffusely adherent *E. coli* (DAEC) pathotype is a group of *E. coli* causing diarrhea that can attach to host cells but not in a localized or A/E adherence pattern [3]. *E. coli* strains belonging to this pathotype binds to the entire surface of the epithelial HEp-2 cells in a scattered pattern termed diffuse adherence. Although the adherence pattern is unique, this pathotype is difficult to classify or identify, a possible reason for the scarce epidemiological studies on this group [177].

DAEC is widespread and associated with diarrhea in both developing and industrialized countries around the world [3]. DAEC strains are associated with watery diarrhea in children under 5 years and can persist resulting in an increase in severity of disease in this age group [177]. DAEC has also been implicated in extraintestinal infections such as UTI, pregnancy complications [3, 177]. It has been speculated that the asymptomatic carriage of DAEC by this age group and adults can lead to chronic inflammatory colon disease such as Crohn's disease [3, 177]. Meanwhile, there is no universal detection method for this pathotype but based on DNA hybridization of fimbrial encoding *daaC* gene probe and adherence pattern to HEp-2 cells of 221 diarrheagenic *E. coli* from different age-groups in Brazil [178], DAEC was identified and shown to be associated with diarrhea in children under 12 months of age in this region. The authors also noted that the presence of DAEC in younger children was not associated with diarrhea, suggesting that the association would probably be based on geographic regions [178]. The asymptomatic carriage by different age groups and the lack of epidemiological data from different regions undermines the development of a universal identification method for this pathotype.

While it is unclear how DAEC is transmitted or its reservoir, the fact that there are asymptomatic carriers could suggest humans as the main reservoir and the fecal-oral route as the primary means of transmission (**Figure 2**). Information regarding serotypes associated with DAEC is scarce. A study of 112 DAEC isolates from diarrheal and asymptomatic individuals in Brazil reported 45 different serotypes, of which 19 were exclusive in patients with diarrhea [179], whereas in another study [180] the serotypes were nontypeable.
