[Norovirus infections].

Noroviruses infect persons of all ages, often causing epidemic outbreaks of acute gastroenteritis as well as sporadic cases. The application of novel molecular methods to the diagnosis of norovirus infections is now revealing their real impact. Molecular epidemiology studies have identified the most common viral genotypes responsible for human infections. Norovirus gastroenteritis is usually mild and of short duration, although the disease can also be severe, especially in the elderly, or may become chronic, as occurred in the immunocompromised patients. Several factors have been identified regarding the differential susceptibility to norovirus infection among individuals, consisting of several histo-blood antigens (ABO, Lewis and secretor) that are involved in the binding process of noroviruses to the enterocytes. The expression of these antigens in humans is genetically encoded, and shows a high polymorphism, which combined with the genetic diversity of noroviruses, makes the virus-host relationship rather complex. The diagnosis of norovirus infections is not performed routinely in many laboratories, but those involved in epidemiological surveillance have identified norovirus strains that evolve sequentially over time, similarly to Influenza viruses.