Diagnosis
- Diarrhea occurring in an outbreak especially in a closed environment
- Tends to infect older children and adults rather than infants
- Nausea and vomiting are common; bloody stools are rare
- Incubation period 1 – 2 days; illness: 1- 4 days
Epidemiology
Even in developed countries, antibodies to calicivirus are nearly universal by age 5. Infections tend to occur in family or community outbreaks. In undeveloped countries, infection by these viruses occurs presumably as a result of poor sanitation. In developed countries, outbreaks that occur year round have been describe in school, resorts, hospital , nursing homes, restaurants and cruise ships.
The primary method of spread is fecal-oral but contaminated water or shell fish has accounted for common source of outbreak. A measure of the importance of these agents is that – 10% of all gastroenteritis outbreaks and up to 90 – 95% of those that are non-bacterial are attributed to them. In contrast to infants, who are more often infected by rotavirus, calicivirus cause disease primarily in older children and adults. Immunity is probably short lived at best, suggesting that humoral antibody is not adequately protective. The incubation period is 1 – 2 days, and shedding can persist for 1- 2 weeks.
The Norwalk agent and related viruses are classified as caliciviruses, although they are also similar in appearance to parvoviruses and hepatitis A virus. Among the other human enteric caliciviruses which are named for where these strains were first detected. The human enteric calicivirus are now divided into two genera, provisionally named “Norwalk like virus” and “Sapporo like virus”.
Symptoms
Although calicilike viruses are typically associated with diarrheal illness, nausea and vomiting may occur frequently, especially in children. Bloody stools do not occur. Fever may be present in up to one third of patients. The incubations period in 24 – 48 hrs and the illness lasts 1 – 4 days.
Calicivirus or Norwalk-like Virus
