Both these viral conditions can occur year round. Incidence is higher in the fall and winter. Norwalk induced gastroenteritis is usually a self-limiting, mild to moderate disease. Clinical symptoms include nausea, vomiting, diarrhea, abdominal pain, headache, malaise, low grade fever or a combination of these symptoms. Gastrointestinal symptoms usually last 24 to 48 hours.
Man is the only known reservoir.
Mode of transmission is not definitely known. The faecal-oral route is considered the most probable. Direct airborne transmission from patient to patient and transmission by fomites has been suggested to explain the rapid spread through hospitals and institutions. Food borne and waterborne outbreaks have also been identified. The organism is very contagious.