Norovirus
Introduction
Most cases of food borne illnesses are relatively mild, with the affected individuals suffering from a few days of gastrointestinal cramping, headache vomiting and/or diarrhea; however some food-borne illness is much more serious, with an estimated 325,000 cases requiring hospitalization and 500 resulting in death in the United States. Similarly, persons who are very young, elderly, pregnant and those with weakened immune systems are especially susceptible to food-borne illness and serious consequences may result (Hui 2006:75).
According to Hui, consumers can reduce the risk by getting a food-borne illness by following safe food handling guidelines when buying, storing, preparing, cooking and serving food at home. In the United States, consumers tend to believe that food prepared at home is an unlikely source of foodborne illness, although studies indicate that most kitchen environments are contaminated with pathogens, and many consumers are unaware of or do not practice safe food handling method (Hui, 2006:75).
As they are thought to cause 10 million deaths per year worldwide and up to 5 billion cases of illness, diarrheal disease from viral gastroenteritis group of viruses is very important (Clapham 2004:102). According to Clapham, they are considered to be the number one cause of acute gastroenteritis in nearly very country in the world, with increasing number of outbreaks in the temperate regions of the world.
According to Hui, of the 13.8 million U.S. food-borne illnesses cause by identified pathogens, viruses are responsible for 9.2 million cases, or 67%. Viruses are extremely small pathogens that are able to reproduce only within the living host cell and do not reproduce in foods, such Norovirus and Hepatitis.
News Timeline Related to Norovirus (Greenberg 2006)
January 1982: Tate, Georgia – 27 patients presented to local physicians during an outbreak of Norwalk-virus gastroenteritis. Illness was characterized by an abrupt onset of abdominal cramps, nausea, diarrhea, and/or vomiting, headache and, low grade fever; after municipal survey, it was found out that as many as 500 people may have been ill during this outbreak. An investigation found that Tate water system was the source for notorious infection
1997-199: Japan – Approximately 265 gastroenteritis cases were reported to be associated with a small round-structured virus, or Norwalk-like virus.
September 1998: Florida – Diarrhea and vomiting was reported by many of the members of the North Carolina football team during a game in Florida. Stool samples tested positive for a genogroup 1 Norwalk-like virus. This case demonstrated close contact, person-to person transmission of the virus.
1999: Toledo, Ohio – Ninety three people who attended the same Christmas dinner developed gastroenteritis. All of the patients had eaten tossed salad prepared by a local caterer; eight received medical attention, and no one was hospitalized. Eight of 12 stool specimens positive for a Norwalk-like virus.
1999: Sweden – An outbreak of gastroenteritis was attributed to a Norwalk-like virus at 30 day-care centers in Sweden.
January 2001 United Kingdom – Thirty eight staff as well as 20 patients of an acute elderly care ward became ill with an outbreak of gastrointestinal infection. The causative agent was found to be a norovirus.
New Delhi: India – after a farewell party, an outbreak of acute gastroenteritis in the nurse’s hostel of hospital was reported. All affected patients had eaten salad sandawiches at the party. Specimens tested positive for genogroup II norovirus.
2001: Northern Wisconsin – An outbreak of gastroenteritis at two summer recreational camps in Wisconsin was reported. The transmission was attributed to person-to-person dissemination of a norovirus.
2001: England, United Kingdom – Forty nine people who developed gastroenteritis were determined to have eaten at the same restaurant the sane weekend prior to symptom onset. Six people showed evidence of norovirus infection. Eating prepared salad was wrongly correlated with illness, and one of the chefs who had been previously been ill with gastrointestinal symptom had been present in the food preparation area
July 2001: Virginia – An outbreak of gastroenteritis aboard 17 cruise ships were reported to CDC’s vessels sanitation program in one calendar year. Of the outbreaks, nine were laboratory confirmed to be associated with norovirus infection. In the previous year (2001), there were four confirmed outbreaks. Norovirus (i.e., Norwalk-like viruses) are part of a group of common microorganisms that cause gastrointestinal symptoms for 24-48 hours. Many reports of cruise-ship outbreaks and resulting disinfection have surfaced over the last years, including the Amsterdam and Disney’s Magic.
September 2005: Mississippi and Texas – As a result of Hurricane Katrina, the Centers for Disease and Control Prevention received reports of approximately 1,000 cases of acute gastroenteritis among hurricane evacuees. Test confirmed norovirus in stool specimens of patients located in Texas
Norovirus, what is it?
Norovirus is the most common cause of food-borne illness in the U.S. because of its low infectious dose, relative to sanitizers and heat, many strains, and the fact that individuals do not acquire long term immunity, but fortunately, the illness is usually mild (Hui 2006:75).
Norovirus refers to a family of unclassified, small, round-structured viruses, often called Norwalk-like virus which is named after Norwalk, Ohio, where the first outbreak was documented in a school cafeteria (Klein 2005:178). According to Klein, today at least 101 viruses are known within the norovirus family of which 99 of these affect humans.
Overall, noroviruses are thought to account for greater than 90% of outbreaks of nonbacterial gastroenteritis worldwide, with the most of these caused by contaminated food and water (Buckman 2006:145). As Buckman reported, susceptibility to norovirus infection is, in part, genetically determined by an individual’s expression of blood group antigens. Individuals who are sector status negative and/or blood group B antigen positive are resistant to infection and disease. Only 10-100 viral particles re are necessary to transmit infection and the virus is resistant to heat, chlorine, and freezing making norovirus an efficient pathogen in food-borne illnesses (Buckman 2006:145).
Noroviruses cause outbreaks in nursing homes, on cruise ships, and in essentially any setting where individuals are confined in close contact. International common source outbreaks related to food and water also can occur. Asymptomatic infection is common, and virus shedding can occur for prolonged periods (2 to 3 weeks) after an individual recover from illness (Schaechter et al. 2007:374). According to Schaechter, transmission of virus from persons asymptomatically shedding virus is likely to be the source of many infections.
Epidemiology
Approximately 3500 laboratory-confirmed cases of norovirus infection are now reported annually in the UK; however, true incidence of disease is likely to be at least 1% of the population per year (Hawker 2005:168). As Hawker reported, all groups are affected: incidence is highest in young children, but severe infection is most frequent in elderly. Infection occurs throughout the year, but reported cases and hospital outbreaks in UK are more common during the cooler months; recorded outbreaks in UK, the Netherlands and Spain occur mainly in hospitals or residential institutions such as nursing homes but are occasionally reported from daycare centers, food outlets, hotels, schools and cruise ships (Hawker 2005: 168).
Host Factors Affect Infection
Early volunteer studies showed that some individuals are resistant to infection with noroviruses and recent studies have found that genetic factors affecting histoblood group antigen expression; including secretor status and ABO blood group type, influence whether an individual becomes infected with Norwalk virus (Schaechter et al. 2007: 375). Nonsectors are resistant to infection and individuals with a blood group type B are less likely to become infected or develop symptomatic infection. According to Scaechter, resistance to other norovirus strains that are genetically distinct from Norwalk virus is not well understood. Norovirus infection induces short term immunity (6-8 weeks) to reinfection and disease, but reinfection with the same strain 1 to 2 years later can again lead to gastroenteritis (Schaechter et al. 2007:375).
Symptoms
The incubation period for norovirus infection ranges from 24-48 hours with a median of 33 hours (Jarvis 2007:569). A spectrum of clinical manifestations has been seen in adults infected with the same virus, with some adults having significant vomiting and diarrhea and others having only diarrhea or vomiting. Common symptoms which are seen in more than 50% of patients include malaise, less frequent chills and fever, small biopsies of infected volunteers show villous blunting in the ileum and proximal jejunum, with the intestinal mucosa remaining intact, and also, gastric emptying is delayed, mal-adsorption of fat, D-xylose, and lactose have been also observed (Schaechter et al. 2007).
Clinical Presentation
Immunity to homologous norovirus challenge is incomplete and short lived. The search for a susceptibility gene has been assisted by the demonstration that norovirus virus like particle (VLP) bind to blood group carbohydrates, and further analysis reveals that Norwalk virus susceptibility is determined by blood group secretor status conferred by the presence of the FUT2 fucosyltransferase (Fields 2007:340). According to fields, among human norovirus strains, at least eight patterns exist of VLP binding to different blood group carbohydrates, strongly suggesting that allelic variations in human blood groups contribute to susceptibility to a variety of norovirus strains demonstrating the profound effect that allelic variations in host genes can have on viral pathogenesis, in this case determining whether a person can be infected with a pathogenic virus.
Norovirus infection causes a decrease in alkaline phosphatase, sucrose and trehalase activities in brush borders of the small intestine resulting in the maladsorption of carbohydrates and steatorrhea. The illness passes without sequellae in most individuals, although rehydration therapy may be necessary in some cases (Fratamico et al. 2005:124). Both stool and vomitus contains infectious particles that can serves as a source of secondary spread. An asyptomatic carrier state occurs in some individuals and can be linked to seroconversion and fecal shedding of viruses.
Laboratory Confirmation and Diagnosis
Diagnosis is traditionally by electron microscopy (EM) of fecal specimens, which should be collected within the first day or two of illness and preferably be unformed; however many laboratories do not routinely test all stools by EM (Hawker 2005:168). According to Hawker, ELISA testing for the most 15 common strains is now widely available and is replacing EM. PCR test, which are much more sensitive than EM, are available from some reference laboratories and genotyping isolates may also be available.
Currently, no commercial diagnostic assays for norovirus are available in the United States, although there are new enzyme-linked immunosorbent assays in Europe (Schaechter et al. 2007).
Other Modes of Transmission
Humans are the only known reservoir of norovirus and spread between humans may occur via: infected food handlers may contaminate food that is eaten raw (e.g. salads) or post cooking, via hands contaminated with feces; contaminated foods: the most commonly contaminated food is shellfish that have concentrated the virus from sewage-contaminated waters and if eaten raw, such shellfish can cause disease (Hawker 2005:168).
Prevention and Control
No vaccines are currently available to prevent norovirus infection, although norovirus are common and highly contagious and require only small inoculums for infection, the risk of infection can be reduced by frequent and appropriate hand hygiene, avoidance of potentially contaminated food and/or water, and adequate disinfection of contaminated environmental surfaces (Jarvis 2007:569).
Strategies successfully used in the past to manage healthcare-associated norovirus outbreaks include the early detection and/or suspicion of norovirus infection; control measures such as isolation or cohorting patients using contact precautions; and, in some instances of ongoing widespread outbreaks, closure of wards or units to new admissions (Jarvis 2007:569). According to Jarvis, because non-enveloped viruses such as norovirus can require a higher a higher concentration of alcohol for inactivation that is commonly available in some ABHR, it is prudent to perform hand washing with soap and water.
Other interventions to minimize secondary transmission include educating of HCWs and patients regarding the risk related to and prevention of norovirus transmission, reinforcing appropriate hand-hygiene measures, and promptly cleaning and containing body fluid spills (Jarvis 2007:569). Similarly, disinfecting of contaminated surfaces with chlorine based products or EPA registered disinfectants with label claims for norovirus or its test surrogate also should be used.
According to Jarvis, if outbreak continue despite this level of disinfection employing an even higher level disinfection with a 1:10 dilution of household bleach as recommended could be beneficial, and the use of proper personal equipment such as gowns, mask and gloves when cleaning up body fluid spills and disinfecting contaminated surfaces is recommended (Jarvis 2007:569).
Everyone should therefore put in mind that in case like this proper knowledge should be applied; everyone should be vigilant in times like a suspicion for norovirus arises. We shouldn’t allow such virus like these to spread. Through early detection and the right action norovirus can be defeated.
List of References
Buckman, A. (2006). Clinical Nutrition in Gastrointestinal Disease. New York: SLACK Incorporated.
Clapham, D. (2004). Small Water Supplies: A Practical Guide. New York: Taylor & Francis.
Entis, P. (2007). Food Safety: Old Habits, New Perspectives. New York: Blackwell Publishing.
Fields, B. N., Knipe, D. M., & Howley, P. M.. (2007). Fields Virology. New York: New York: Lippincott Williams.
Fratamico, P. M., Bhunia, A. K., & Smith, J. L. (2005). Foodborne Pathogens: Microbiology and Molecular Biology. New York: Horizon Scientific Press.
Gibson, P. (2006). Cruise Operations Management. New York: Butterworth-Heinemann.
Greenberg, M. I. (2006). Encyclopedia of Terrorist, Natural, and Man-Made Disasters. New York: Jones & Bartlett.
Hawker, J. (2005). Communicable Disease Control Handbook. New York: Blackwell Publishing.
Hui, Y. H. (2006). Handbook of Food Science, Technology, and Engineering. New York: CRC Press.
Jarvis, W. R. (2007). Bennett and Brachman’s Hospital Infections. New York: Lippincott Williams & Wilkins.
Klein, R. A. (2005). Cruise Ship Squeeze: The New Pirates of the Seven Seas. New York: New Society Publishers.
Mays, L. W. (2004). Water Supply Systems Security. New York: McGraw-Hill Professional.
Riemann, H, & Cliver, D. O. (2006). Foodborne Infections and Intoxications. New York: Academics Press.
Schaechter, M., Engleberg, N. C., DiRita, V. J., & Dermody, T. (2007). Schaechter’s Mechanisms of Microbial Disease. . New York: Lippincott Williams & Wilkins.