AUTHOR AND EDITOR INFORMATION

Section 1 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

INTRODUCTION

Section 2 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Background

Noroviruses are a group of single-stranded RNA viruses in the family Caliciviridae that cause acute gastroenteritis in humans. Norwalk virus is the prototypical strain in the genus. Norovirus infection is an important cause of acute gastroenteritis in humans and is the most frequently implicated cause of outbreaks of viral gastroenteritis worldwide. Noroviruses cause an estimated 20% of all viral gastroenteritis cases in persons older than 24 months.

Norwalk virus was first associated with gastroenteritis in 1972. It was identified by electron microscopy of stool samples that had been saved from a 1968 gastroenteritis epidemic that occurred in Norwalk, Ohio. In a 2-day period, acute gastroenteritis developed in 50% of 232 students or teachers in an elementary school. The virus initially was labeled as a small, round, structured virus, and it was named after the city in which the outbreak occurred. Recently, norovirus infections have made news as the cause of several outbreaks of gastroenteritis on cruise ships.

Pathophysiology

The viruses are transmitted via the fecal-oral route. The most common routes of infection include contact with an infected individual or contact with contaminated food and water. Noroviruses can also be spread via particles aerosolized with vomiting. The viruses are highly contagious; only 100 viral particles are likely required to establish infection. Noroviruses can survive freezing and heating temperatures of up to 140°F. Infection is characterized by damage to microvilli in the small intestine, causing malabsorption. Vomiting is related to a virus-mediated change in gastric motility and delayed gastric emptying. Notably, no histopathologic lesions are identified in the gastric mucosa of infected patients. Noroviruses do not invade the colon, therefore fecal leukocytes are typically absent and hematochezia is rare.

Recurrent infections can occur throughout life because of the diversity of norovirus strains and the lack of cross-strain or long-term immunity.

Frequency

United States

• The frequency of norovirus disease in the United States is difficult to quantify because of the lack of readily available diagnostic assays. Recent efforts to determine the etiology of diarrheal diseases in the United States have suggested that noroviruses cause up to 17% of community cases of diarrhea and 7% of cases that require physician treatment.

Among 232 outbreaks of norovirus gastroenteritis reported to the Centers for Diseases Control between 1997 and 2000, 57% were foodborne, 16% involved person-to-person spread, 3% were waterborne, and the remainder were unknown. The location of these outbreaks included restaurants (36%), nursing homes (23%), schools (13%), and resorts/cruise ships (10%). In September 2005, an outbreak of norovirus gastroenteritis affected approximately 1000 Hurricane Katrina evacuees in temporary facilities in Houston, Tex. This episode illustrates the increased risk of such outbreaks in overcrowded conditions.

International

Data regarding outbreaks in developing nations are not well quantified, but the outbreak rate in other industrial nations is similar to that of the United States.

Mortality/Morbidity

Norovirus gastroenteritis typically lasts 24-48 hours. Death is extremely rare except in those particularly vulnerable to dehydration.

CLINICAL

Section 3 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

History

• Symptomatic gastroenteritis typically develops 24-48 hours after ingestion of contaminated food or water or after contact with an infected individual. Each episode is short-lived, lasting approximately 1-2 days.
• Complaints include the following:
• • Nausea and vomiting (profuse, nonbloody, nonbilious)
  • Watery diarrhea
  • Abdominal cramps
  • Headache
  • Low-grade fever
  • Myalgia

Physical

• Vital signs include low-grade fever, tachycardia, possible hypotension (if dehydrated).
• Fecal leukocytes are absent.
• Abdominal examination findings include the absence of both focal tenderness and peritoneal signs.

Causes

• Contaminated water supply
• Frequently implicated foods include salad, cake frosting, clams, oysters, and meats.
• Viral shedding
• • The virus is shed in vomitus and feces.
  • Contamination can occur through an infected water supply, undercooked foods, or improper hand washing by an infected food preparer.
  • Because of viral shedding during profuse vomiting and diarrhea, secondary transmission commonly occurs among close contacts of the infected person.
  • The virus causes infection with a low inoculum exposure (100 viral particles) and is stable with freezing or temperatures of up to 140°F.
  • Cruise ships are particularly vulnerable because of frequent changes in the passenger cohort, relative crowding, and the difficulty in performing decontamination during short periods at shore.

DIFFERENTIALS

Section 4 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

WORKUP

Section 5 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Lab Studies

• Isolated occurrences of gastroenteritis do not require laboratory studies.
• In severe cases of gastroenteritis with suspected dehydration, the following laboratory studies are indicated.
• • Serum electrolytes
  • BUN and creatinine
• Detection:
• • Detection can be achieved with polymerase chain reaction (PCR) or electron microscopy. Newer diagnostic modalities such as microarrays are currently under investigation.
  • Referral laboratories typically can evaluate stool isolates for noroviruses.
  • Because the studies are very costly, stool evaluation is not recommended unless strong public health indications exist.
• Epidemic outbreaks
• • More than 2 people living in different households who shared a common meal or 3 or more people living in the same household
  • Stool culture for Yersinia, Shigella, Salmonella, and Campylobacter species
  • Stool for occult blood
  • Fecal leukocytes
• In an epidemic setting, the health department may choose to further evaluate stool with PCR for noroviruses.

Imaging Studies

• Imaging for isolated, uncomplicated gastroenteritis is not required.
• If acute abdomen or toxic ingestion is suspected, an abdominal series is indicated.

Other Tests

• If the patient is a returning international traveler, stool tests for ova and parasites or specialized stool cultures for cholera may be considered.
• If the patient is severely immunocompromised (AIDS), stool tests for Cyclospora, cytomegalovirus (CMV), Isospora, and Cryptosporidium may be considered

Histologic Findings

• Stool culture will be negative for infectious bacteria. Stool is typically heme-negative and fecal leukocytes will be absent.
• Vomitus will be heme-negative and nonbilious.

TREATMENT

Section 6 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Medical Care

• Outpatient therapy is typically sufficient.
• • Oral rehydration
  • Rest
  • Contact exposure precautions (increase handwashing)
• Inpatient therapy for severe dehydration
• • Intravenous hydration
  • Electrolyte monitoring and replacement

Consultations

For all epidemic outbreaks (2 or more people who shared a common meal), local and/or state health department should be contacted for investigation of potential sources.

Diet

• Electrolyte replacement liquids
• General diet as tolerated

Activity

Activity may be performed as tolerated.

MEDICATION

Section 7 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Disease is usually self-limited to 24-48 hours. Antidiarrheal agents may be used sparingly but should be avoided in children.

FOLLOW-UP

Section 8 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Deterrence/Prevention:

• Secondary spread of infection can be prevented through appropriate hand washing and disposal of infectious materials.
• In an inpatient setting, contact isolation precautions will help limit nosocomial spread.
• Notify the health department so it can investigate outbreak centers and prevent further transmission.

Complications:

• Severe dehydration can lead to hypovolemic shock and cardiovascular collapse.
• Electrolyte abnormality
• • Metabolic alkalosis
  • Hyponatremia
  • Hypokalemia
  • Hypochloremia
• Exacerbates inflammatory bowel disease
• Rare cases of extraintestinal manifestations such as encephalopathy have been reported in pediatric patients.

Prognosis:

• Prognosis for full recovery in 24-48 hours is excellent.

Patient Education:

• Disease transmission may be decreased with education regarding hand washing for food preparers, daycare employees, resort/cruise guests, and family or close contacts of infected individuals.

MISCELLANEOUS

Section 9 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Medical/Legal Pitfalls

• Notify state or local health departments of all suspected norovirus outbreaks (>2 people who shared a common meal) so that potential outbreak centers can be investigated and further transmission limited.

REFERENCES

Section 10 of 10

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

• Blacklow NR, Greenberg HB. Viral gastroenteritis. N Engl J Med. Jul 25 1991;325(4):252-64. [Medline].
• Centers for Disease Control and Prevention (CDC). Outbreaks of gastroenteritis associated with noroviruses on cruise ships--United States, 2002. MMWR Morb Mortal Wkly Rep. Dec 13 2002;51(49):1112-5. [Medline].
• Centers for Disease Control and Prevention (CDC). Norovirus outbreak among evacuees from hurricane Katrina--Houston, Texas, September 2005. MMWR Morb Mortal Wkly Rep. Oct 14 2005;54(40):1016-8.
• Centers for Disease Control and Prevention (CDC). Multisite outbreak of norovirus associated with a franchise restaurant--Kent County, Michigan, May 2005. MMWR Morb Mortal Wkly Rep. Apr 14 2006;55(14):395-7.
• DuPont HL. Guidelines on acute infectious diarrhea in adults. The Practice Parameters Committee of the American College of Gastroenterology. Am J Gastroenterol. Nov 1997;92(11):1962-75. [Medline].
• Graham DY, Jiang X, Tanaka T. Norwalk virus infection of volunteers: new insights based on improved assays. J Infect Dis. Jul 1994;170(1):34-43. [Medline].
• Greenberg HB, Valdesuso J, Yolken RH. Role of Norwalk virus in outbreaks of nonbacterial gastroenteritis. J Infect Dis. May 1979;139(5):564-8. [Medline].
• Guerrant RL, Shields DS, Thorson SM. Evaluation and diagnosis of acute infectious diarrhea. Am J Med. Jun 28 1985;78(6B):91-8. [Medline].
• ICTVdb. The Universal Virus Database of the International Committee on Taxonomy of Viruses Web site. Available at: http://ictvdb.bio2.columbia.edu/Ictv/index.htm. Accessed on December 27, 2002.
• Ito S, Takeshita S, Nezu A, et al. Norovirus-associated encephalopathy. Pediatr Infect Dis J. Jul 2006;25(7):651-652.
• Jaaskelainen AJ, Maunula L. Applicability of microarray technique for the detection of noro- and astroviruses. J Virol Methods. Jun 15 2006.
• Jiang X, Wang M, Graham DY. Expression, self-assembly, and antigenicity of the Norwalk virus capsid protein. J Virol. Nov 1992;66(11):6527-32. [Medline].
• Kaplan JE, Gary GW, Baron RC. Epidemiology of Norwalk gastroenteritis and the role of Norwalk virus in outbreaks of acute nonbacterial gastroenteritis. Ann Intern Med. Jun 1982;96(6 Pt 1):756-61. [Medline].
• Koplan JP, Fineberg HV, Ferraro MJ. Value of stool cultures. Lancet. Aug 23 1980;2(8191):413-6. [Medline].
• Moe CL, Gentsch J, Ando T. Application of PCR to detect Norwalk virus in fecal specimens from outbreaks of gastroenteritis. J Clin Microbiol. Mar 1994;32(3):642-8. [Medline].
• Shewmake RA, Dillon B. Food poisoning. Causes, remedies, and prevention. Postgrad Med. Jun 1998;103(6):125-9, 134, 136. [Medline].
• Siegel DL, Edelstein PH, Nachamkin I. Inappropriate testing for diarrheal diseases in the hospital. JAMA. Feb 16 1990;263(7):979-82. [Medline].

Article Last Updated: Jun 30, 2006