Norovirus
Norovirus (formerly Norwalk virus) is an RNA virus (taxonomic family Caliciviridae) which causes approximately 90% of epidemic non-bacterial outbreaks of gastroenteritis around the world,[1] and may be responsible for 50% of all foodborne outbreaks of gastroenteritis in the US.[2][3] Norovirus affects people of all ages. The viruses are transmitted by faecally contaminated food or water and by person-to-person contact.[4]
After infection, immunity to norovirus is usually incomplete and temporary.[5] There is an inherited predisposition to infection, and individuals with blood type O are more often infected,[1][6] while blood types B and AB can confer partial protection against symptomatic infection.[7][8]
Outbreaks of norovirus infection often occur in closed or semi-closed communities, such as long-term care facilities, overnight camps, hospitals, prisons, dormitories, and cruise ships where the infection spreads very rapidly by either person-to-person transmission or through contaminated food.[9] Many norovirus outbreaks have been traced to food that was handled by one infected person.[10]
Norovirus is rapidly inactivated by sufficient heating and by chlorine-based disinfectants, but the virus is less susceptible to alcohols and detergents as it does not have a lipid envelope.[11]
Norovirus Symptoms and course of illness
When a person becomes infected with norovirus, the virus begins to multiply within the small intestine. After approximately 1 to 2 days, norovirus symptoms can appear. The principal symptom is acute gastroenteritis that develops between 24 and 48 hours after exposure, and lasts for 24–60 hours.[3] The disease is usually self-limiting, and characterised by nausea, vomiting, diarrhea, and abdominal pain; and in some cases, loss of taste. General lethargy, weakness, muscle aches, headache, and low-grade fever may occur.
Severe illness is rare: although people are frequently treated at the emergency ward, they are rarely admitted to the hospital. The number of deaths from norovirus in the US is estimated to be around 300 each year, with most of these occurring in the very young, elderly and persons with weakened immune systems. Symptoms may become life-threatening in these groups if dehydration is ignored or not treated.[4]
The most common genotype identified in hospitalized children was GII.4 and increased amount of virus (7.2 x 107) were shed by those children. Even though GII.4 Norovirus was the most common identified, other genotypes were identified in less proportion, including the novel GII.18-NICA.[citation needed]
Norovirus Diagnosis
Specific diagnosis of norovirus is routinely made by polymerase chain reaction (PCR) assays or real-time PCR assays, which give results within a few hours. These assays are very sensitive and can detect concentrations as low as 10 virus particles.[15]
Tests such as ELISA that use antibodies against a mixture of norovirus strains are available commercially but lack specificity and sensitivity.[16]
Epidemiology, Norovirus prevention and infection control
Noroviruses are transmitted directly from person to person and indirectly via contaminated water and food. They are highly contagious, with as few as ten virus particles being able to cause infection. Transmission occurs through ingesting contaminated food and water and by person-to-person spread. Transmission is predominantly faecal-oral but may be airborne due to aerosolisation of vomit. Norovirus can be aerosolized when those stricken with the illness vomit; infection can follow eating food near an episode of vomiting, even if cleaned up[17].
Norovirus is extremely infectious. In one outbreak at an international scout jamboree in the Netherlands, each person with gastroenteritis infected an average of 14 people before increased hygiene measures were put in place. Even after these new measures were enacted an average ill person still infected 2.1 other people.[18] A CDC study of eleven outbreaks in New York State lists the suspected mode of transmission as person-to-person in seven outbreaks, foodborne in two, waterborne in one, and one unknown. The source of waterborne outbreaks may include water from municipal supplies, wells, recreational lakes, swimming pools and ice machines.[19]
Shellfish and salad ingredients are the foods most often implicated in norovirus outbreaks. Ingestion of shellfish that have not been sufficiently heated poses a high risk for norovirus infection. Foods other than shellfish may be contaminated by infected food handlers.[20]
Hand washing is an effective method to reduce the spread of norovirus pathogens. Sanitizing of surfaces where the norovirus may be present is recommended.
In health-care environments, the prevention of nosocomial infections involves routine and terminal cleaning. Nonflammable alcohol vapor in CO2 systems are used in health care environments where medical electronics would be adversely affected by aerosolized chlorine or other caustic compounds.[21]
Ligocyte announced in 2007 that it was working on a vaccine and had started phase 1 trials.[22]
Epidemiological data from developing countries about the importance of norovirus in pediatric diarrhea is limited. Recently, in Nicaragua has been observed that norovirus is responsible for 11% of the diarrhea cases occurring in children <5 years of age at community level and 15% of the moderate to severe cases requiring intravenous re-hydration.[23]
Detection of norovirus in foods
Routine protocols to detect norovirus (norovirus RNA) in clams and oysters by RT-PCR (reverse transcription polymerase chain reaction) are being employed by governmental laboratories such as the FDA in the USA. However, routine methods to detect the virus on other food items are not readily available due to the variable nature of different food items affecting concentration and extraction of the virus and presence of factors that make PCR (Polymerase chain reaction) analysis techniques ineffective.[24]