NLE1 and hemolytic-uremic syndrome: However, the presence of LEE- and nle-genes is not essential for STEC pathogenesis and sporadic cases and small outbreaks of STEC infections, including HC and HUS, have been caused by LEE-negative strains (Keskimaki et al., 1997; Bonnet et al., 1998; Paton et al., 1999).