The illness is usually relatively mild, develops 12 to 48 hours after exposure, and clears within a couple of days without treatment. Additionally, these viruses sometimes cause projectile vomiting. The signs and symptoms of norovirus infection are similar to those for rotavirus, with watery diarrhea, mild cramps, and fever. Because the virus is not killed by disinfectants used at standard concentrations for killing bacteria, the risk of transmission remains high, even after cleaning. The viruses can be transmitted through direct contact, through touching contaminated surfaces, and through contaminated food. They are known for causing widespread infections in groups of people in confined spaces, such as on cruise ships. These viruses are easily transmitted and highly contagious. There are millions of cases a year, predominately in infants, young children, and the elderly. Several strains can cause gastroenteritis. Noroviruses, commonly identified as Norwalk viruses, are caliciviruses. The WHO recommends that all infants worldwide receive the rotavirus vaccine, the first dose between six and 15 weeks of age and the second before 32 weeks. In the United States, rotavirus vaccines are part of the standard vaccine schedule and administration follows the guidelines of the World Health Organization (WHO). Preventive vaccination is also available. Treatment is supportive with oral rehydration therapy. Additionally, the virus can be detected using electron microscopy and RT-PCR. Latex agglutination assays are also used. The most common clinical tool for diagnosis is enzyme immunoassay, which detects the virus from fecal samples. Patients (especially children) who are malnourished after an episode of diarrhea are more susceptible to future diarrheal illness, increasing their risk of death from rotavirus infection. Even with milder illness, repeated infections can potentially lead to malnutrition, especially in developing countries, where rotavirus infection is common due to poor sanitation and lack of access to clean drinking water. Without supportive treatment, the illness can cause severe fluid loss, dehydration, and even death. The illness generally appears after an incubation period of about two days and lasts for approximately one week (three to eight days). Infection can cause food intolerance, especially with respect to lactose. The virus can survive in the stomach following a meal, but is normally found in the small intestines, particularly the epithelial cells on the villi. Infected individuals exhibit fever, vomiting, and diarrhea. The virus can also be transmitted from contaminated surfaces, on which it can survive for some time. In these cases, the infection may be transmitted from a family member who may have subclinical or clinical disease.

The elderly, however, are vulnerable to rotavirus infection due to weakening of the immune system with age, so infections can spread through nursing homes and similar facilities. Due to the memory of the bodyвЂ™s immune system, adults who come into contact with rotavirus will not contract the infection or, if they do, are asymptomatic. The CDC estimates that 95% of children in the United States have had at least one rotavirus infection by the time they reach age five. These viruses are widespread in children, especially in day-care centers.

The virus is primarily spread by the fecal-oral route (FigureВ 1). They are responsible for common diarrheal illness, although prevention through vaccination is becoming more common. Rotaviruses are double-stranded RNA viruses in the family Reoviridae. Rotaviruses in a fecal sample are visualized using electron microscopy.

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