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==Overview==
==Overview==
[[Norovirus]]es are a group of [[virus]]es that cause [[gastroenteritis]], which is commonly known as the "[[stomach flu]]" or "[[food poisoning]]", in people. The term norovirus was recently approved as the official name for this group of viruses. Norovirus  is a very [[contagious]] virus. One can get norovirus from an infected person, [[contamination|contaminated]] food or water, or by touching contaminated surfaces. The virus causes [[stomach]] or [[intestine]]s or both to get [[inflammation|inflamed]] ([[acute gastroenteritis]]). This  leads to [[stomach pain]], [[nausea]], and [[diarrhea]] and to [[vomit]]. Anyone can be infected with norovirus and get sick. Also, norovirus infection can occur many times in life. Norovirus illness can be serious, especially for young children and older adults. Norovirus is the most common cause of [[acute gastroenteritis]] in the United States. Each year, it causes about 21 million illnesses and contributes to about 70,000 hospitalizations and 800 deaths. Norovirus is also the most common cause of foodborne-disease outbreaks in the United States. The best way to help prevent norovirus is to practice proper hand washing and general cleanliness.
[[Norovirus]]es (Norwalk) infection is the most common cause of acute gastroenteritis. Norovirus is a single-stranded [[RNA]], non-enveloped virus. Norovirus  is a highly [[contagious]] virus. It is often transmitted via [[contamination|contaminated]] food or water, or by touching contaminated surfaces. Norovirus  gastroenteritis results in [[abdominal pain]] (usually diffuse, stabbing pain), [[nausea]], [[diarrhea]] (usually watery), and [[vomiting]]. There is no age or gender predisposition to the development of norovirus infection. Risk factors for norovirus infection include close contact with infected individuals, particularly those in the same household, poor food-handling [[hygiene]], and consumption of contaminated shellfish and/or raw vegetables. Symptoms of norovirus infection start within 12 to 48 hours of exposure to the virus and usually last 24 to 72 hours. Patients usually recover completely without treatment (only hydration) and without any serious long-term sequalae. Young children, elderly, and immunocompromised patients are at a higher risk of complications. In rare cases, norovirus illness can be serious, especially for young children and older adults. Lab findings are usually non-specific and may only be remarkable for signs of dehydration, such as elevated BUN and creatinine, relative polycythemia, and metabolic alkalosis. Real-time PCR is the optimal method for the diagnosis of norovirus infection. Supportive care is the mainstay of therapy for norovirus infection. Treatment includes oral/IV fluid administration to replace fluids lost from [[vomiting]] and [[diarrhea]] and to [[electrolyte disturbances]]. Other pharmacologic agents, such as anti-motility and anti-emetic agents may be administered among adults only (controversial efficacy), whereas anti-diarrheal agents are usually not recommended. Preventive measures include avoidance of exposure, proper hand washing, and adequate handling of food products.  
 
==Historical Perspective==
Originally called the "Norwalk agent" after Norwalk, Ohio, Norovirus was first discovered after an outbreak in an elementary school in 1968. The first documentation of the virus on electron microscopy was in 1972.
==Classification==
Norovirus constitutes a genus of genetically diverse single-stranded RNA, non-enveloped viruses belonging to the ''[[Caliciviridae]]'' family. The Norwalk virus is the only species belonging to that genus; however, several strains have been identified including: Hawaii virus, Mexico virus, and Desert Shield virus. These strains can genetically be classified into five different genogroups (GI, GII, GIII, GIV, and GV).
==Pathophysiology==
==Pathophysiology==
Norovirus is a highly [[contagious]] virus. Anyone can get infected with norovirus and get sick. Also, one can get norovirus illness many times in life. One reason for this is that there are many different types of noroviruses. Being infected with one type of norovirus may not protect one against other types. Norovirus can be found in your [[stool]] (feces) even before one starts feeling sick. The virus can stay in stool for 2 weeks or more after one feels better.
Noroviruses are highly [[contagious]], given that as few as 10 particles are enough to cause the disease, [[transmission]] is via the fecal-oral route and peaks during the period when symptoms are most severe, and up to 3 days after recovery. As many strains of noroviruses exist, immunity is not gained following an [[infection]]. A non-functional [[fucosyltransferase]] FUT2 mutation has been associated with protection against the most common norovirus strains as FUT2 is required for viral transport in the [[small intestine]].
==Causes==
==Causes==
[[Norovirus]] causes norovirus infection in people. Noroviruses ([[genus]] Norovirus, family [[Caliciviridae]]) are a group of related, single-stranded [[RNA]], nonenveloped viruses that cause acute gastroenteritis in humans. Norovirus was recently approved as the official genus name for the group of viruses provisionally described as “Norwalk-like viruses” (NLV). Noroviruses belong to the family Caliciviridae that includes sapoviruses, which also causes [[acute gastroenteritis]].
[[Norovirus]] is the cause of norovirus infection. Noroviruses ([[genus]] Norovirus) are a group of related, single-stranded [[RNA]], nonenveloped viruses that cause acute gastroenteritis in humans. Noroviruses belong to the family Caliciviridae.
 
==Differentiating Norovirus from other Diseases==
Norovirus should be differentiated from other causes of infectious [[vomiting]] and [[diarrhea]], including other causes of viral gastroenteritis ([[sapovirus]], [[adenovirus]], [[rotavirus]]), bacterial gastroenteritis ([[yersinia]], [[vibrio]], [[shigella]], [[salmonella]], [[escherichia coli]]), and parasitic infections ([[amoebiasis]], [[cryptosporidiosis]]).
 
==Epidemiology and Demographics==
Norovirus is the leading cause of [[acute gastroenteritis]] and foodborne illness in all age groups in the United States. It causes approximately 21 million cases of [[gastroenteritis]] yearly. The genogroup II, genotype 4 strain is most commonly involved in large [[outbreaks]] of norovirus.
 
==Risk Factors==
==Risk Factors==
Noroviruses are transmitted directly via person to person or indirectly via contaminated water and foods. A [[Centers for Disease Control and Prevention|CDC]] study of eleven outbreaks in [[New York|New York State]] lists  the suspected [[Transmission (medicine)|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. <ref name="pmid8395330">{{cite journal
Risk factors for norovirus infection include close contact with infected individuals, particularly those in the same household, poor food-handling [[hygiene]], and consumption of contaminated shellfish and/or raw vegetables.
|author=Hedberg CW, Osterholm MT
|title=Outbreaks of food-borne and waterborne viral gastroenteritis
|journal=Clin. Microbiol. Rev.
|volume=6
|issue=3
|pages=199–210
|year=1993
|pmid=8395330
|doi=
|url=http://cmr.asm.org/cgi/pmidlookup?view=long&pmid=8395330
|issn=
}}</ref>


[[Shellfish]] and [[salad]] ingredients are the foods most often implicated in Norwalk outbreaks. Ingestion of raw or insufficiently steamed [[clam]]s and [[oyster]]s poses a high risk for infection with the Norwalk virus. Foods other than shellfish are contaminated by ill food handlers.<ref name="pmid11479930">{{cite journal
|author=Parashar UD, Monroe SS
|title="Norwalk-like viruses" as a cause of foodborne disease outbreaks
|journal=Rev. Med. Virol.
|volume=11
|issue=4
|pages=243–52
|year=2001
|pmid=11479930
|doi=10.1002/rmv.321
|issn=
}}</ref>
==Natural History, Complications and Prognosis==
==Natural History, Complications and Prognosis==
The [[incubation period]] for norovirus-associated [[gastroenteritis]] in humans is usually between 24 and 48 hours ([[median]] in outbreaks 33 to 36 hours), but cases can occur within 12 hours of exposure. Recovery is usually complete and there is no evidence of any serious long-term sequelae.
Symptoms of norovirus infection start within 12 to 48 hours of exxposure to the virus and usually last 24 to 72 hours. Patients usually recover completely without treatment (only hydration) and without any serious long-term sequalae. Young children, elderly, and immunocompromised patients are at a higher risk of complications.
 
==Diagnosis==
==Diagnosis==
===History and Symptoms===
===History and Symptoms===
Norovirus infection usually presents as acute-onset [[vomiting]], watery non-bloody [[diarrhea]] with [[abdominal cramps]], and [[nausea]]. [[Low-grade fever]] also occasionally occurs, and vomiting is more common in children. [[Dehydration]] is the most common complication, especially among the young and elderly, and may require medical attention. Symptoms usually last 24 to 60 hours.
Symptoms of norovirus infection include malaise, fever, stabbing diffuse abdominal pain, diarrhea, vomiting, and anorexia. Parents of infected children may often report easy irritability and oliguria/anuria.
===Physical Examination===
===Physical Examination===
Norovirus infection can present as mild febrile illnesss or a severe [[febrile]] illness with temperatures of 101-102 F.
Physical examination of patients with norovirus infection may be remarkable for low-grade fever, tachycardia, abdominal tenderness, and signs of dehydration (reduced skin turgor, sunken fontanelles, sunken eyes, dry mucous membranes). Physical examination in severe cases may be remarkable for hypotension and altered mental status.
===Laboratory Findings===
===Laboratory Findings===
In the last 10 years, diagnosis of norovirus as cause of [[outbreak]]s of acute gastroenteritis has improved with the increasing use of the [[reverse transcriptase polymerase chain reaction]] ([[RT-PCR]]). Currently, state public health laboratories of 47 states have the capability to test for noroviruses by (realtime) [[RT-PCR]]. [[RT-PCR]] detects the [[norovirus]] [[RNA]] and can be used to test [[stool]] and [[emesis]] samples, as well as environmental swabs in special studies. Identification of the virus can be best made from stool specimens taken within 48 to 72 hours after onset of [[symptom]]s, although good results can be obtained by using RT-PCR on samples taken as long as 5 days after symptom onset. Virus can sometimes be found in stool samples taken as late as 2 weeks after recovery.
Laboratory findings of norovirus infection include elevated concentration of inflammatory markers, hypokalemia, and chloride-sensitive metabolic alkalosis. Signs of dehydration may be present, such as relative polycythemia, elevated BUN, and elevated creatinine (pre-renal acute kidney injury). RT-qPCR assay is the optimal test for the diagnosis of norovirus infection. Enzyme immunoassays to detect norovirus have been developed but are less useful due to low sensitivity. Norovirus is not usually grown on culture.


Sequencing of norovirus strains found in clinical and environmental samples has greatly helped in conducting epidemiologic investigations by linking cases to each other and to a common source and by differentiating outbreaks that were mistakenly connected. Sequences can be entered into CaliciNet, a recently developed [[sequence database]] on the basis of the PulseNet model. In the next years CaliciNet will be further implemented to be able to help to determine links (e.g., norovirus [[contamination|contaminated]] foods) between outbreaks across the U.S.
Older methods for diagnosis include direct and immune [[electron microscopy]] of [[fecal]] specimens, and detection of a fourfold increase of specific [[antibodies]] in acute- and [[convalescent]]-phase blood samples. Several commercially available [[enzyme-linked immunosorbent assay]]s for detection of virus in stools have been developed but await evaluation further evaluation regarding [[sensitivity]] and [[specificity]].
==Treatment==
==Treatment==
===Medical Therapy===
===Medical Therapy===
There is no specific medicine to treat people with norovirus illness. Norovirus infection cannot be treated with [[antibiotic]]s because it is a [[viral]] (not a [[bacteria]]l) [[infection]]. Patients with norovirus infection should drink plenty of liquids to replace fluid lost from throwing up and [[diarrhea]]. This will help prevent [[dehydration]]. Sports drinks and other drinks without caffeine or alcohol can help with mild dehydration. But, these drinks may not replace important nutrients and minerals. Oral rehydration fluids that you can get over the counter are most helpful for mild dehydration. Dehydration can lead to serious problems. Severe dehydration may require hospitalization for treatment with [[intravenous fluid]]s).
Supportive care is the mainstay of therapy for norovirus infection. Treatment includes oral/IV fluid administration to replace fluids lost from [[vomiting]] and [[diarrhea]] and to [[electrolyte disturbances]]. Over the counter oral rehydration solutions (ORS) are usually available, but home-made ORS may be prepared by mixing 1 liter of clean drinking water, 0.5 teaspoon of salt, and 6 teaspoons of sugar. Anti-motility and anti-emetic agents may be administered for symptomatic relief among adults only (controversial efficacy). Antimicrobial agents, including antiviral agents, are generally not recommended to treat norovirus infection.  
===Primary Prevention===
===Primary Prevention===
There is no [[vaccine]] to prevent norovirus [[infection]]. Prevention of [[foodborne]] norovirus disease is based on the provision of safe food and water. Noroviruses are relatively resistant to environmental challenge: they are able to survive freezing, temperatures as high as 60°C, and have even been associated with illness after being steamed in shellfish. Moreover, noroviruses can survive in up to 10 ppm [[chlorine]], well in excess of levels routinely present in public water systems. Despite these features, it is likely that relatively simple measures, such as correct handling of cold foods, strict hand washing after using the bathroom and before handling food items, and paid sick leave, may substantially reduce foodborne transmission of noroviruses. Prevention of norovirus disease spread via droplets from [[vomitus]] (person to person [[transmission]]) should focus on methods to limit transmission including [[isolation (health care)|isolation]] precautions (e.g., cohort sick patients in a healthcare facility) and environmental [[disinfection]].
There is no [[vaccine]] to prevent norovirus [[infection]]. Prevention of [[foodborne]] norovirus disease is based on the provision of safe food and water. Noroviruses are relatively resistant to temperature changes and have been associated with illness after eating steamed shellfish. Moreover, noroviruses can survive in up to 10 ppm [[chlorine]], well in excess of levels routinely present in public water systems. Despite these features, it is likely that relatively simple measures, such as correct handling of cold foods, strict hand washing after using the bathroom and before handling food items, and paid sick leave, may substantially reduce foodborne transmission of noroviruses. Prevention of norovirus disease spread via droplets from [[vomitus]] (person to person [[transmission]]) should focus on methods that limit transmission including: [[isolation (health care)|isolation]] precautions (e.g. isolating sick patients in a healthcare facility) and environmental [[disinfection]].
 
===Secondary Prevention===
==Videos==
The [[CDC]] currently does not conduct active [[disease surveillance|surveillance]] to monitor [[outbreak]]s of [[gastroenteritis]] caused by [[norovirus]]es. The National Outbreak Reporting System (NORS) is a web-based system that was launched by the CDC in 2009 to collect information on outbreaks of foodborne, waterborne, and enteric diseases that spread from person-to-person, animals, environmental surfaces, and other or unknown ways. Public health agencies can report all outbreaks of gastroenteritis, including norovirus illness. The CDC also developed CaliciNet in 2009. It is a network of public health and food regulatory laboratories that submit norovirus sequences identified from outbreaks into a national database.
{{#ev:youtube|BWf8XVZ8MEs}}
 
{{#ev:youtube|TMMw1iS46DA}}
 
{{#ev:youtube|n-R6SP1lYdI}}
 
{{#ev:youtube|OFxoxW_TdKw}}


== References ==
== References ==
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[[Category:Disease]]
[[Category:Disease]]
[[Category:Infectious disease]]
 
[[Category:Needs overview]]
[[Category:Needs overview]]
[[Category:Viral diseases]]
[[Category:Viral diseases]]

Latest revision as of 18:13, 18 September 2017

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

Noroviruses (Norwalk) infection is the most common cause of acute gastroenteritis. Norovirus is a single-stranded RNA, non-enveloped virus. Norovirus is a highly contagious virus. It is often transmitted via contaminated food or water, or by touching contaminated surfaces. Norovirus gastroenteritis results in abdominal pain (usually diffuse, stabbing pain), nausea, diarrhea (usually watery), and vomiting. There is no age or gender predisposition to the development of norovirus infection. Risk factors for norovirus infection include close contact with infected individuals, particularly those in the same household, poor food-handling hygiene, and consumption of contaminated shellfish and/or raw vegetables. Symptoms of norovirus infection start within 12 to 48 hours of exposure to the virus and usually last 24 to 72 hours. Patients usually recover completely without treatment (only hydration) and without any serious long-term sequalae. Young children, elderly, and immunocompromised patients are at a higher risk of complications. In rare cases, norovirus illness can be serious, especially for young children and older adults. Lab findings are usually non-specific and may only be remarkable for signs of dehydration, such as elevated BUN and creatinine, relative polycythemia, and metabolic alkalosis. Real-time PCR is the optimal method for the diagnosis of norovirus infection. Supportive care is the mainstay of therapy for norovirus infection. Treatment includes oral/IV fluid administration to replace fluids lost from vomiting and diarrhea and to electrolyte disturbances. Other pharmacologic agents, such as anti-motility and anti-emetic agents may be administered among adults only (controversial efficacy), whereas anti-diarrheal agents are usually not recommended. Preventive measures include avoidance of exposure, proper hand washing, and adequate handling of food products.

Historical Perspective

Originally called the "Norwalk agent" after Norwalk, Ohio, Norovirus was first discovered after an outbreak in an elementary school in 1968. The first documentation of the virus on electron microscopy was in 1972.

Classification

Norovirus constitutes a genus of genetically diverse single-stranded RNA, non-enveloped viruses belonging to the Caliciviridae family. The Norwalk virus is the only species belonging to that genus; however, several strains have been identified including: Hawaii virus, Mexico virus, and Desert Shield virus. These strains can genetically be classified into five different genogroups (GI, GII, GIII, GIV, and GV).

Pathophysiology

Noroviruses are highly contagious, given that as few as 10 particles are enough to cause the disease, transmission is via the fecal-oral route and peaks during the period when symptoms are most severe, and up to 3 days after recovery. As many strains of noroviruses exist, immunity is not gained following an infection. A non-functional fucosyltransferase FUT2 mutation has been associated with protection against the most common norovirus strains as FUT2 is required for viral transport in the small intestine.

Causes

Norovirus is the cause of norovirus infection. Noroviruses (genus Norovirus) are a group of related, single-stranded RNA, nonenveloped viruses that cause acute gastroenteritis in humans. Noroviruses belong to the family Caliciviridae.

Differentiating Norovirus from other Diseases

Norovirus should be differentiated from other causes of infectious vomiting and diarrhea, including other causes of viral gastroenteritis (sapovirus, adenovirus, rotavirus), bacterial gastroenteritis (yersinia, vibrio, shigella, salmonella, escherichia coli), and parasitic infections (amoebiasis, cryptosporidiosis).

Epidemiology and Demographics

Norovirus is the leading cause of acute gastroenteritis and foodborne illness in all age groups in the United States. It causes approximately 21 million cases of gastroenteritis yearly. The genogroup II, genotype 4 strain is most commonly involved in large outbreaks of norovirus.

Risk Factors

Risk factors for norovirus infection include close contact with infected individuals, particularly those in the same household, poor food-handling hygiene, and consumption of contaminated shellfish and/or raw vegetables.

Natural History, Complications and Prognosis

Symptoms of norovirus infection start within 12 to 48 hours of exxposure to the virus and usually last 24 to 72 hours. Patients usually recover completely without treatment (only hydration) and without any serious long-term sequalae. Young children, elderly, and immunocompromised patients are at a higher risk of complications.

Diagnosis

History and Symptoms

Symptoms of norovirus infection include malaise, fever, stabbing diffuse abdominal pain, diarrhea, vomiting, and anorexia. Parents of infected children may often report easy irritability and oliguria/anuria.

Physical Examination

Physical examination of patients with norovirus infection may be remarkable for low-grade fever, tachycardia, abdominal tenderness, and signs of dehydration (reduced skin turgor, sunken fontanelles, sunken eyes, dry mucous membranes). Physical examination in severe cases may be remarkable for hypotension and altered mental status.

Laboratory Findings

Laboratory findings of norovirus infection include elevated concentration of inflammatory markers, hypokalemia, and chloride-sensitive metabolic alkalosis. Signs of dehydration may be present, such as relative polycythemia, elevated BUN, and elevated creatinine (pre-renal acute kidney injury). RT-qPCR assay is the optimal test for the diagnosis of norovirus infection. Enzyme immunoassays to detect norovirus have been developed but are less useful due to low sensitivity. Norovirus is not usually grown on culture.

Treatment

Medical Therapy

Supportive care is the mainstay of therapy for norovirus infection. Treatment includes oral/IV fluid administration to replace fluids lost from vomiting and diarrhea and to electrolyte disturbances. Over the counter oral rehydration solutions (ORS) are usually available, but home-made ORS may be prepared by mixing 1 liter of clean drinking water, 0.5 teaspoon of salt, and 6 teaspoons of sugar. Anti-motility and anti-emetic agents may be administered for symptomatic relief among adults only (controversial efficacy). Antimicrobial agents, including antiviral agents, are generally not recommended to treat norovirus infection.

Primary Prevention

There is no vaccine to prevent norovirus infection. Prevention of foodborne norovirus disease is based on the provision of safe food and water. Noroviruses are relatively resistant to temperature changes and have been associated with illness after eating steamed shellfish. Moreover, noroviruses can survive in up to 10 ppm chlorine, well in excess of levels routinely present in public water systems. Despite these features, it is likely that relatively simple measures, such as correct handling of cold foods, strict hand washing after using the bathroom and before handling food items, and paid sick leave, may substantially reduce foodborne transmission of noroviruses. Prevention of norovirus disease spread via droplets from vomitus (person to person transmission) should focus on methods that limit transmission including: isolation precautions (e.g. isolating sick patients in a healthcare facility) and environmental disinfection.

Secondary Prevention

The CDC currently does not conduct active surveillance to monitor outbreaks of gastroenteritis caused by noroviruses. The National Outbreak Reporting System (NORS) is a web-based system that was launched by the CDC in 2009 to collect information on outbreaks of foodborne, waterborne, and enteric diseases that spread from person-to-person, animals, environmental surfaces, and other or unknown ways. Public health agencies can report all outbreaks of gastroenteritis, including norovirus illness. The CDC also developed CaliciNet in 2009. It is a network of public health and food regulatory laboratories that submit norovirus sequences identified from outbreaks into a national database.

References


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