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NOROVIRUS Norwalk Agent:

NOROVIRUS Norwalk Agent Dr.T.V.Rao MD Dr.T.V.Rao MD 1

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. History of Norovirus Dr.T.V.Rao MD 2


Norovirus (formerly Norwalk agent ) is an RNA 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 Norovirus Dr.T.V.Rao MD 3


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

Norovirus are Diverse Group:

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

Norovirus Characteristics:

Norovirus Characteristics Highly contagious Multiple modes of transmission Stable in the environment Resistant to routine disinfection methods Carriers may not be symptomatic Adapted from Strategies for Norovirus Infection Control Aboard Cruise Ships , Robert E. Wheeler, MD, 2003. Dr.T.V.Rao MD 6

Norovirus characteristics:

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

Norovirus Infection :

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 more Adapted from Strategies for Norovirus Infection Control Aboard Cruise Ships , Robert E. Wheeler, MD, 2003. Dr.T.V.Rao MD 8

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 Outbreaks of Norovirus Dr.T.V.Rao MD 9

Why is Norovirus so infectious?:

High attack rate (> 50%) and low infective dose (10-100 particles) Viral load may be >10 7 /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 Why is Norovirus so infectious?

Pathophysiology :

When a person becomes infected with Norovirus, the 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. Pathophysiology Dr.T.V.Rao MD 11

Criteria for Norovirus infection:

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


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

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. Food Handlers and Norovirus Dr.T.V.Rao MD 14

Norovirus Transmission :

Norovirus Transmission Transmission “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

Modes of Transmission by Food :

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

Susceptibility of Norovirus:

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


Symptoms Symptoms usually start within 24 to 48 hours after exposure. Vomiting Watery diarrhea Stomach Cramping. Low grade fever occurs in half of cases Dr.T.V.Rao MD 18

Norovirus Infection Symptoms :

Norovirus Infection Symptoms Vomiting Diarrhea Nausea Abdominal cramps Headache, muscle aches Fever (minority) Dehydration Up to 30% may be asymptomatic Adapted from Strategies for Norovirus Infection Control Aboard Cruise Ships , Robert E. Wheeler, MD, 2003. Dr.T.V.Rao MD 19

Specific Diagnosis:

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

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 Scheme for molecular detection of Norovirus

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 Molecular tools for tracing sources of infection: : Norovirus Genotyping Dr.T.V.Rao MD 22


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

Control of Norovirus outbreaks :

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

Clean and disinfect contaminated surfaces:

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

Caring the laundry procedures:

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

Hand Washing Still the best option to prevent infection:

Dr.T.V.Rao MD 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.

Care of the Hands Reduces Norovirus Infections:

Dr.T.V.Rao MD 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

CDC guidelines for Norovirus Prevention:

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

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Created by Dr.T.V.Rao MD for ‘e’ learning resources for the Medical Professionals in Developing World Email Dr.T.V.Rao MD 30

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