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  1. 1. Norwalk Agent Dr.T.V.Rao MD Dr.T.V.Rao MD 1
  2. 2. History of Norovirus The Norovirus was originally named the Norwalk agent after Norwalk, Ohio, USA, where an outbreak of acute gastroenteritis occurred among children at Bronson Elementary School in November 1968. The name was shortened to Norovirus after being identified in a number of outbreaks on cruise ships and receiving attention throughout the USA. In 1972, electron microscopy on stored human stool samples identified a virus, which was given the name Norwalk virus. Dr.T.V.Rao MD 2
  3. 3. Norovirus  agent) is an RNA Norovirus (formerly Norwalk virus (taxonomic family Caliciviridae) that causes approximately 90% of epidemic non-bacterial outbreaks of gastroenteritis around the world, and may be responsible for 50% of all foodborne outbreaks of gastroenteritis in the US. Norovirus affects people of all ages. The viruses are transmitted by faecally contaminated food or water, by person- to-person contact, and via aerosolization of the virus and subsequent contamination of surfaces Dr.T.V.Rao MD 3
  4. 4. Norovirus Formerly called Norwalk-like Virus Highly contagious Cause of 50% of all foodborne outbreaks of gastroenteritis Able to survive freezing and high temperatures Dr.T.V.Rao MD 4
  5. 5. Norovirus are Diverse Group Norovirus (NoV) are a  genetically diverse group of single stranded RNA, nonenvelopedd viruses belonging to the Caliciviridae family. According to the International Committee on Taxonomy of Virus, the genus Norovirus has one species, which is called "Norwalk virus" and assigned the abbreviation "NV". Serotypes, strains and isolates include: Dr.T.V.Rao MD 5
  6. 6. Norovirus Characteristics  Highly contagious Multiple modes of transmission Stable in the environment Resistant to routine disinfection methods Carriers may not be symptomaticAdapted from Strategies for Norovirus Infection Control Aboard Cruise Ships, Robert E. Wheeler, MD, 2003. Dr.T.V.Rao MD 6
  7. 7. Norovirus characteristics  Cause epidemic gastroenteritis Replicate in human intestinal mucosal cells to produce gastroenteritis Human Norovirus not generally able to be grown in culture yet Mechanism of pathogenicity still unknown Genetically variable: many distinct human strains in 2 major genogroups Norovirus characteristics cause limitations for detection methods Dr.T.V.Rao MD 7
  8. 8. Norovirus Infection   Infectious dose of 10-100 virus particles  24-48 hour incubation period  12-60 hour duration of illness  A ―mild‖ and short-lived illness  Treatment may indicate IV fluids  Viral shedding of 3 weeks or moreAdapted from Strategies for Norovirus Infection Control Aboard Cruise Ships, Robert E. Wheeler, MD, 2003. Dr.T.V.Rao MD 8
  9. 9. Outbreaks of Norovirus  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 either by person-to- person transmission or through contaminated food.[ Many Norovirus outbreaks have been traced to food that was handled by one infected person Dr.T.V.Rao MD 9
  10. 10. Why is Norovirus so infectious?  High attack rate (> 50%) and low infective dose (10-100 particles) Viral load may be >107/g faeces Viral shedding can occur for > 14 days Little or no immunity following infection Environmentally tough - resistant to acid, heat, disinfectants, chemicals, drying etc. Secondary person-to-person spread via vomit, aerosols and fomites Dr.T.V.Rao MD 10
  11. 11. Pathophysiology  with Norovirus, the When a person becomes infected 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. The disease is usually self-limiting, and characterized 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. Dr.T.V.Rao MD 11
  12. 12. Criteria for Norovirus infection  Stool culture negative for bacterial pathogens Mean duration of illness 12-60 hr Vomiting in > 50% of cases, (more common in children whereas adults have diarrhoea). Projectile vomiting often a characteristic symptom Incubation period is 24-48 hr but may be 10 - 50hr Previously no diagnostic methods were available so commonly known as acute non-bacterial gastroenteritis Ref: Kaplan et al. Am J Pub Health 1982;72:1329-32) Dr.T.V.Rao MD 12
  13. 13. Transmission  Fecal-oral route Indirect contact with the virus on contaminated surfaces. Via contaminated food and water Shellfish from sewage contaminated water Dr.T.V.Rao MD 13
  14. 14. Food Handlers and Norovirus  Persons working with food who are sick with Norovirus gastroenteritis are a particular risk to others because they handle the food and drink many other people will consume. The virus is very small and shed (discharged from the body through vomit or stool) in great numbers. Thus—without meaning to—a sick food handler can easily contaminate the food he or she is handling. Many of those eating the contaminated food may become ill, and an outbreak may result. Dr.T.V.Rao MD 14
  15. 15. Norovirus TransmissionTransmission  ―Oral-fecal‖ route Food (39%) Hands, person-to- person (12%) Water (3%) Also environmental surfaces: carpets, toilets, etc.Adapted from Strategies for Norovirus Infection Control Aboard Cruise Ships, Robert E. Wheeler, MD, 2003. Dr.T.V.Rao MD 15
  16. 16. Modes of Transmission by Food  Food sources (i.e., food arrives contaminated) Preparation Food handlers Customers Most at risk: ready-to-eat foods that require handling but no subsequent cooking (e.g., salads)Adapted from Strategies for Norovirus Infection Control Aboard Cruise Ships, Robert E. Wheeler, MD, 2003. Dr.T.V.Rao MD 16
  17. 17. Susceptibility of Norovirus  Norovirus is rapidly inactivated by either sufficient heating or by chlorine-based disinfectants, but the virus is less susceptible to alcohols and detergents as it does not have a lipid envelope. Dr.T.V.Rao MD 17
  18. 18. Symptoms  24 to 48 hours after Symptoms usually start within exposure.VomitingWatery diarrheaStomach Cramping.Low grade fever occurs in half of cases Dr.T.V.Rao MD 18
  19. 19. Norovirus Infection Symptoms  Vomiting Diarrhea Nausea Abdominal cramps Headache, muscle aches Fever (minority) Dehydration Up to 30% may be asymptomaticAdapted from Strategies for Norovirus Infection Control Aboard Cruise Ships, Robert E. Wheeler, MD, 2003. Dr.T.V.Rao MD 19
  20. 20. Specific 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 Dr.T.V.Rao MD 20
  21. 21. Scheme for molecular detection of Norovirus Specimen Processing (Faeces) Viral Recovery & RNA extraction Generate cDNA from RNA by reverse transcription Amplify by real-time PCR Norovirus Genogroup I or II identified Sequencing Genotyping
  22. 22. Molecular tools for tracing sources of infection: : Norovirus Genotyping  Sequence Norovirus PCR product from faeces Compare sequence with similar sequences in CDC & other databases and determine % similarity between Norovirus DNA sequences Only short DNA fragments are compared (100-200 bp) not whole virus genome Compare prevalent outbreak strains with strains occurring at same time in NZ & internationally Dr.T.V.Rao MD 22
  23. 23. Treatment There is no specific treatment.Persons with diarrhea and/or vomiting should drink plenty of liquids to prevent dehydration.Medications, including antibiotics (which have no effect on viruses) and other treatments, should be avoided unless specifically recommended by a physician. Dr.T.V.Rao MD 23
  24. 24. Control of Norovirus outbreaks  Secondary spread via aerosols & vomit is a major problem Isolation of patients, staff and infected areas Staff may excrete noroviruses for up to 14 days – should they be checked for clearance? Thorough surface cleaning (benches, taps, fomites, furniture, floors etc.) Good hand washing practices: some hand disinfectants are not effective for all viruses Refer specimens for viral analysis and genotyping to help track movement of epidemic strains Dr.T.V.Rao MD 24
  25. 25. Clean and disinfect contaminated surfaces  After an episode of illness, such as vomiting or diarrhea, immediately clean, disinfect, and rinse contaminated surfaces. Use a chlorine bleach solution with a concentration of 1000– 5000 ppm (5–25 tablespoons of household bleach [5.25%] per gallon of water) Dr.T.V.Rao MD 25
  26. 26. Caring the laundry procedures Linens (towels,  tablecloths, napkins) and clothing that are soiled to any extent with vomit or stool should be handled carefully—without agitating the item—to avoid spreading virus. The items should be laundered with detergent at the maximum available cycle length and then machine dried Dr.T.V.Rao MD 26
  27. 27. Hand Washing Still the best option to prevent infection Wash your hands carefully  with soap and water, especially after using the toilet and before preparing or handling food. Norovirus are found in the vomit and stool of infected people from the day they start to feel ill, and the virus continues to be present in the stool for as long as 2 to 3 weeks after an infected person feels better. Dr.T.V.Rao MD 27
  28. 28. Care of the Hands Reduces Norovirus Infections  Continued care in washing hands is important in preventing the spread of this virus. Alcohol-based hand sanitizers (containing at least 62% ethanol) may be a helpful addition to hand washing, but they are not a substitute for washing with soap and water Dr.T.V.Rao MD 28
  29. 29. CDC guidelines for Norovirus Prevention The guidelines include  recommendations related to patient cohorting and isolation precautions, hand hygiene, patient transfer and ward closure, indirect patient care staff, diagnostics, personal protective equipment, environmental cleaning, staff leave, visitors, education, and communication. Dr.T.V.Rao MD 29
  30. 30. Created by Dr.T.V.Rao MD for ‘e’ learning resources forthe Medical Professionals in Developing World  Email  Dr.T.V.Rao MD 30