ETEC infections among young children in endemic regions are thought to result in acquired immunity and a decreasing incidence of infection with age.9 Indeed, controlled human infection studies demonstrate that homologous re-challenge with the ETEC H10407 strain, which encodes CFA/I, results in robust protection against symptomatic ETEC infection.10 However, precise correlates of protection11 have not been established, and the majority of immunologic studies have focused on canonical virulence factors, namely the CF/CS antigens and heat-labile toxin. This evidence concerns the gene CS and infection.