What do you need to know about Norovirus during an Outbreak

What is Norovirus?

The Centers for Disease Control and Prevention (CDC) estimates that noroviruses cause nearly 21 million cases of acute gastroenteritis annually, making noroviruses the leading cause of gastroenteritis in adults in the United States. 

Nature has created an ingenious bug in norovirus. The round blue ball structure of norovirus is a protein surrounding the virus’s genetic material. The virus attaches to the outside of cells lining the intestine, and then transfers its genetic material into those cells. Once the genetic material has been transferred, norovirus reproduces, finally killing the human cells and releasing new copies of itself that attach to more cells of the intestine’s lining.

Humans are the only host of norovirus, and norovirus has several mechanisms that allow it to spread quickly and easily. Norovirus infects humans in a pathway like the influenza virus’ mode of infection. In addition to their similar infective pathways, norovirus and influenza also evolve to avoid the immune system in a similar way. Both viruses are driven by heavy immune selection pressure and antigenic drift, allowing evasion of the immune system, which results in outbreaks. Norovirus can survive a wide range of temperatures and in many different environments. Moreover, the viruses can spread quickly, especially in places where people are in proximity, such as cruise ships and airline flights, even those of short duration. 

How is Norovirus transmitted?

Norovirus causes nearly 60% of all foodborne illness outbreaks. Norovirus is transmitted primarily through the fecal-oral route, with fewer than 100 norovirus particles needed to cause infection. Transmission occurs either person-to-person or through contamination of food or water. CDC statistics show that food is the most common vehicle of transmission for noroviruses; of 232 outbreaks of norovirus between July 1997 and June 2000, 57% were foodborne, 16% were spread from person-to-person, and 3% were waterborne. When food is the vehicle of transmission, contamination occurs most often through a food handler improperly handling a food directly before it is eaten.

Infected individuals shed the virus in large numbers in their vomit and stool, shedding the highest number of viral particles while they are ill. Aerosolized vomit has also been implicated as a mode of norovirus transmission. Previously, it was thought that viral shedding ceased approximately 100 hours after infection; however, some individuals continue to shed norovirus long after they have recovered from it, in some cases up to 28 days after experiencing symptoms. Viral shedding can also precede symptoms, which occurs in approximately 30% of cases. Often, an infected food handler may not even show symptoms.

What are the Symptoms & Risks of a Norovirus Infection?

Norovirus illness usually develops 24 to 48 hours after ingestion of contaminated food or water. Symptoms typically last a relatively short amount of time, approximately 24 to 48 hours. These symptoms include nausea, vomiting, diarrhea, and abdominal pain.  Headache and low-grade fever may also accompany this illness. People infected with norovirus usually recover in two to three days without serious or long-term health effects. 

Although symptoms usually only last one to two days in healthy individuals, norovirus infection can become quite serious in children, the elderly, and immune-compromised individuals. In some cases, severe dehydration, malnutrition, and even death can result from norovirus infection, especially among children and among older and immune-compromised adults in hospitals and nursing homes.

How do you Diagnose a Norovirus Infection?

Diagnosis of norovirus illness is based on the combination of symptoms, particularly the prominence of vomiting, little fever, and the short duration of illness.  If a known norovirus outbreak is in progress, public health officials may obtain specimens from ill individuals for testing in a lab. These lab tests consist of identifying norovirus under an electron microscope. 

How do you Treat a Norovirus Infection?

There is no specific treatment available for norovirus. In most healthy people, the illness is self-limiting and resolves in a few days; however, outbreaks among infants, children, elderly, and immune-compromised populations may result in severe complications among those affected. Death may result without prompt measures. The replacement of fluids and minerals such as sodium, potassium and calcium – otherwise known as electrolytes – lost due to persistent diarrhea is vital. This can be done either by drinking large amounts of liquids, or intravenously.

How do you Prevent a Norovirus Infection?

Common settings for norovirus outbreaks include restaurants and events with catered meals (36%), nursing homes (23%), schools (13%), and vacation settings or cruise ships (10%). Proper hand washing is the best way to prevent the spread of norovirus. 

Shellfish (oysters, clams, mussels) pose the greatest risk and any serving may be contaminated with norovirus; there is no way to detect a contaminated oyster, clam, or mussel from a safe one.  Shellfish become contaminated when their waters become contaminated—e.g., when raw sewage is dumped overboard by recreational or commercial boaters). Shellfish are filter feeders and will concentrate virus particles present in their environment. With shellfish, only complete cooking offers reliable protection; steaming does not kill the virus or prevent its transmission. 

References

1. American Public Health Association (APHA), Heymann, David L., editor, “Norovirus Infection,” in CONTROL OF COMMUNICABLE DISEASES MANUAL, pp. 227-29, (18^th Ed. 2008).
2. Antonio, J, et al., “Passenger Behaviors During Norovirus Outbreaks on Cruise Ships,” INTERNATIONAL SOCIETY OF TRAVEL MAGAZINE, Vol. 15, No. 3, pp. 172-176 (May-June 2008). Abstract available online at http://www.ncbi.nlm.nih.gov/pubmed/18494694
3. Benson, V. and Merano, M.A., “Current estimates from the National Health Interview Survey 1995,” VITAL HEALTH STATISTICS, SERIES 10 (Nat’l Center for Health Statistics 1998). Abstract available online at http://www.ncbi.nlm.nih.gov/pubmed/9914773
4. Cáceres, VM, et al., “A viral gastroenteritis outbreak associated with person-to-person spread among hospital staff,” INFECTION CONTROL AND HOSPITAL EPIDEMIOLOGY, Vol. 19, No. 3, pp. 162-7 (March 1998). Abstract available online at http://www.ncbi.nlm.nih.gov/pubmed/9552183
5. CDC, Norovirus:  Technical Fact Sheet, from Centers for Disease Control and Prevention Web site,http://www.cdc.gov/ncidod/dvrd/revb/gastro/norovirus-factsheet.htm (last modified on August 24, 2011) (last checked on Jan. 3, 2012). 
6. CDC, Norovirus in Healthcare Facilities Fact Sheet, released December 21, 2006, available through Centers for Disease Control and Prevention website, at http://www.cdc.gov/ncidod/dvrd/revb/gastro/downloads/noro-hc-facilities-fs-508.pdf (last checked on January 4, 2012).
7. CDC, Facts about Norovirus on Cruise Ships, last updated July 20, 2009, available through the Centers for Disease Control and Prevention website, at http://www.cdc.gov/nceh/vsp/pub/Norovirus/Norovirus.htm (last checked on January 4, 2012). 
8. CDC, “Outbreaks of Gastroenteritis Associated with Noroviruses on Cruise Ships – United States, 2002,” MORBIDITY AND MORTALITY WEEKLY REPORT, Vol. 51, No. 49, pp. 1112-15 (Dec. 13, 2002). Full text available online at http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5149a2.htm
9. CDC, “Updated Norovirus Outbreak Management and Disease Prevention Guidelines,” MORBIDITY AND MORTALITY WEEKLY REPORT, Vol. 60, Recommendations and Reports No. 3, pp. 1-15 (March 4, 2011). Full text available online at http://www.cdc.gov/mmwr/preview/mmwrhtml/rr6003a1.htm
10. CDC, “Norwalk-like viruses’—Public health consequences and outbreak management,” MORBIDITY AND MORTALITY WEEKLY REPORT, Vol. 50, Recommendations and Reports No. 9, pp. 1-18 (June 1, 2001). Full text available online at http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5009a1.htm
11. Duizer, E, et al., “Probabilities in norovirus outbreak diagnosis,” JOURNAL OF CLINICAL VIROLOGY, Vol. 40, No. 1, pp. 38-42 (Sept. 2007). Abstract available online at http://www.ncbi.nlm.nih.gov/pubmed/17631044
12. Donaldson, E., et al., “Viral shape-shifting: norovirus evasion of the human immune system,” NATURE REVIEWS, MICROBIOLOGY, Vol. 8, No. 3, pp. 231-239 (March 2010). Abstract available online at http://www.ncbi.nlm.nih.gov/pubmed/20125087
13. Fankhauser, RL, et al., “Epidemiologic and molecular trends of ‘Norwalk-like viruses’ associated with outbreaks of gastroenteritis in the United States,” JOURNAL OF INFECTIOUS DISEASES, Vol.186, No. 1, pp. 1-7 (July 1, 2002). Full text of article available online at http://jid.oxfordjournals.org/content/186/1/1.long
14. Gerencher, Christine L., Reporter, “Understanding How Disease Is Transmitted via Air Travel: Summary of a Symposium,” Conference Proceedings 47, Transportation Research Board of the National Academies (2010). Full summary available online at http://onlinepubs.trb.org/onlinepubs/conf/CP47.pdf
15. Glass, RI, et al., “The Epidemiology of Enteric Caliciviruses from Humans: A Reassessment Using New Diagnostics,” JOURNAL OF INFECTIOUS DISEASES, Vol. 181, Supplement 2, pp. S254-61 (2000). Full text available online at http://jid.oxfordjournals.org/content/181/Supplement_2/S254.long
16. Glass, R, Parashar, U.D., and Estes, M.K., “Norovirus Gastroenteritis,” NEW ENGLAND JOURNAL OF MEDICINE, Vol. 361, No. 18, pp. 1776-1785 (Oct. 29, 2009). Full text available online at http://www.sepeap.org/archivos/pdf/11191.pdf
17. Janneke, C, et al., “Enhanced Hygiene Measures and Norovirus Transmission during an Outbreak,” EMERGING INFECTIOUS DISEASES, Vol. 15, No., pp. 24-30 (Jan. 2009). Full text available online at http://wwwnc.cdc.gov/eid/article/15/1/08-0299_article.htm
18. Harris, JP, et al., “Deaths from Norovirus among the Elderly, England and Wales,” EMERGING INFECTIOUS DISEASES, Vol. 14, No. 10, pp. 1548-1552 (Oct. 2008). Full text available online athttp://wwwnc.cdc.gov/eid/article/14/10/08-0188_article.htm
19. Kirkland, KB, et al., “Steaming oysters does not prevent Norwalk-like gastroenteritis,” PUBLIC HEALTH REPORTS, Vol. 111, pp. 527-30 (1996). Full text available online at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1381901/pdf/pubhealthrep00045-0057.pdf
20. Maunula, L, Miettinen, IT, and Bonsdorff, CH, “Norovirus Outbreaks from Drinking Water,” EMERGING INFECTIOUS DISEASES, Vol. 11, No. 11, pp. 1716-1721 (2005).  Full text available online at http://wwwnc.cdc.gov/eid/content/11/11/pdfs/v11-n11.pdf
21. Lopman, Ben, Zambon, Maria, and Brown, David, “The Evolution of Norovirus, the ‘Gastric Flu,’” Public Library of Science: Medicine, Vol. 5, Issue 2, pp.187-189 (Feb. 2010). Full text available online at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2235896/pdf/pmed.0050042.pdf
22. Lowther, J, Henshilwood, K, and Lees DN, “Determination of Norovirus Contamination in Oysters from Two Commercial Harvesting Areas over an Extended Period, Using Semiquantitative Real-Time Reverse Transcription PCR,” JOURNAL OF FOOD PROTECTION, Vol. 71, No. 7, pp. 1427-1433 (2008). Abstract available online at http://www.ncbi.nlm.nih.gov/pubmed/18680943
23. Lysen, M, et al., “Genetic Diversity among Food-Borne and Waterborne Norovirus Strains Causing Outbreaks in Sweden,” JOURNAL OF CLINICAL MICROBIOLOGY, Vol. 47, No. 8, pp. 2411-2418 (2009). Full text available online at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2725682/?tool=pubmed
24. Marks, PJ, et al., “Evidence of airborne transmission of Norwalk-like virus (NLV) in a hotel restaurant,” EPIDEMIOLOGY AND INFECTION, Vol. 124, No. 3, pp. 481-87 (June 2000). Full text available online at http://www.cdc.gov/nceh/ehs/Docs/Evidence_for_Airborne_Transmission_of_Norwalk-like_Virus.pdf
25. Mayo Clinic, “Norovirus Infection,” Mayo Clinic Web site, information last updated April 15, 2011 (as of last checking on Jan. 3, 2012), available online at http://www.mayoclinic.com/health/norovirus/DS00942/DSECTION=1. 
26. Mead, Paul M, et al., “Food-related Illness and Death in the United States,” EMERGING INFECTIOUS DISEASES, Vol. 5, No. 5, pp. 607-25 (September-October 1999). Full text available online at  http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2627714/pdf/10511517.pdf
27. Middleton, PJ, Szmanski, MT, and Petric M, “Viruses associated with acute gastroenteritis in young children,” AMERICAN JOURNAL OF DISEASES OF CHILDREN, Vol. 131, No. 7, pp. 733-37 (July 1977). Abstract available online at http://www.ncbi.nlm.nih.gov/pubmed/195461
28. Patterson, T, Hutchin, P, and Palmer S, “Outbreak of SRSV gastroenteritis at an international conference traced to food handled by a post symptomatic caterer,” EPIDEMIOLOGY AND INFECTION,  Vol. 111, No. 1, pp. 157-162 (Aug. 1993). Available online at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2271183/?tool=pubmed
29. Ozawa, K, et al., “Norovirus Infections in Symptomatic and Asymptomatic Food Handlers in Japan,” JOURNAL OF CLINICAL MICROBIOLOGY, Vol. 45, No. 12, pp. 3996-4005 (Oct. 2007). Abstract available online at http://jcm.asm.org/content/45/12/3996.abstract
30. Said, Maria, Perl, Trish, and Sears Cynthia, “Gastrointestinal Flu: Norovirus in Health Care and Long-Term Care Facilities,” HEALTHCARE EPIDEMIOLOGY, vol. 47, pp. 1202-1208 (Nov. 1, 2008). Full text available online at http://cid.oxfordjournals.org/content/47/9/1202.full.pdf+html
31. Scallan, E., et al., “Foodborne Illness Acquired in the United States—Major Pathogens,” EMERGING INFECTIOUS DISEASES, Vol. 17, No. 1, pp. 7-15 (2011). Full text available online at http://wwwnc.cdc.gov/eid/article/17/1/p1-1101_article.htm
32. Siebenga, JJ, et al., “Norovirus Illness Is a Global Problem: Emergence and Spread of Norovirus GII.4 Variants, 2001–2007,” JOURNAL OF INFECTIOUS DISEASES, Vol. 200, No. 5, pp. 802-812 (2009). Full text available online at http://jid.oxfordjournals.org/content/200/5/802.long
33. Treanor, John J. and Dolin, Raphael, “Norwalk Virus and Other Calciviruses,” in Mandell, Douglas, and Bennett’s PRINCIPLES AND PRACTICE OF INFECTIOUS DISEASES, Fifth Edition, Chap. 163, pp. 1949-56 (2000, Mandell, Bennett, and Dolan, Editors).
34. Tu, E.T., et al., “Epidemics of Gastroenteritis during 2006 Were Associated with the Spread of Norovirus GII.4 Variants 2006a and 2006b,” CLINICAL INFECTIOUS DISEASES, Vol. 46, No. 3, pp. 413-420 (Feb. 1, 2008). Full text available online at http://cid.oxfordjournals.org/content/46/3/413.full
35. Tu E.T., et al., “Norovirus excretion in an age-care setting,” JOURNAL OF CLINICAL MICROBIOLOGY, Vol. 46, pp. 2119-21 (June 2008). Full text available online at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2446857/pdf/2198-07.pdf
36. Verhoef, L, et al., “Emergence of New Norovirus Variants on Spring Cruise Ships and Prediction of Winter Epidemics,” EMERGING INFECTIOUS DISEASES, Vol. 14, No. 2, pp. 238-243 (Feb. 2008). Full text available online at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2600213/pdf/06-1567_finalR.pdf
37. Vinje, J, “A Norovirus Vaccine on the Horizon?” EMERGING INFECTIOUS DISEASES, Vol. 202, No. 11, pp. 1623-1625 (2010). Full text available online at http://jid.oxfordjournals.org/content/202/11/1623.full
38. Westrell T, et al., “Norovirus outbreaks linked to oyster consumption in the United Kingdom, Norway, France, Sweden and Denmark,”  EURO-SURVEILLANCE (European Communicable Disease Bulletin), Vol. 15, No. 12 (Mar. 25 2010). Full text available online at http://www.eurosurveillance.org/images/dynamic/EE/V15N12/art19524.pdf

Republished with permission from Bill Marler and Marler Clark. Copyright (c) Marler Clark LLP, PS. All rights reserved.