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Norwalk Virus Presentation to Board of Public Health Duxbury, Massachusetts March 20, 2003 David Brumley, MD, MBA Sources: Centers for Disease Control The Merck Manual* *Copyright © 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002 Merck & Co., Inc., Whitehouse Station, NJ, USA. All rights reserved. Noroviruses l l l Norwalk-like viruses (NLVs) Caliciviruses (because they belong to the virus family Caliciviridae) Small round structured viruses. History l Noroviruses are named after the original strain “Norwalk virus,” which caused an outbreak of gastroenteritis in a school in Norwalk, Ohio, in 1968. Epidemiology l l l l l Occurs year-round Outbreaks of norovirus gastroenteritis have taken place in restaurants, cruise ships, nursing homes, hospitals, schools, banquet halls, summer camps, and family dinners. CDC estimates that 23 million cases of acute gastroenteritis are due to norovirus infection. It is estimated that as many as half of all food-related outbreaks of illness may be caused by norovirus. Waterborne outbreaks of norovirus disease in community settings have often been caused by sewage contamination of wells and recreational water. Sites of Infection l Among the 232 outbreaks of norovirus illness reported to CDC from July 1997 to June 2000, – – – l 57% were foodborne 16% were due to person-to-person spread 3% were waterborne Common settings for outbreaks – – – – restaurants and catered meals (36%) nursing homes (23%) schools (13%) vacation settings or cruise ships (10%) Transmission l l Noroviruses are found in the stool or vomit of infected people. become infected with the virus in several ways, including: – – – l eating food or drinking liquids that are contaminated with norovirus; touching surfaces or objects contaminated with norovirus, and then placing their hand in their mouth; having direct contact with another person who is infected and showing symptoms (for example, when caring for someone with illness, or sharing foods or eating utensils with someone who is ill). The virus is very contagious and can spread rapidly throughout nursing home and day care environments. Transmission l l l l l l Both stool and vomit are infectious. It is thought that as few as 10 viral particles may be sufficient to infect an individual. Particular care should be taken with young children in diapers who may have diarrhea. People infected with norovirus are contagious from the moment they begin feeling ill to at least 3 days after recovery. Some people may be contagious for as long as 2 weeks after recovery Asymptomatic infection may occur in as many as 30% of infections, Symptoms l l l l l Typically nausea, vomiting, diarrhea, and some stomach cramping. People who are sick with norovirus illness can often vomit violently, without warning, and the vomit is infectious. Sometimes low-grade fever, chills, headache, muscle aches, and a general sense of tiredness. Often begins suddenly, and the infected person may feel very sick. Usually brief, with symptoms lasting only about 1 or 2 days. Course of Illness l l l l Symptoms of norovirus illness usually begin about 24 to 48 hours after ingestion of the virus, but they can appear as early as 12 hours after exposure. There are many different strains of norovirus, which makes it difficult for a person’s body to develop long-lasting immunity Norovirus illness can recur throughout a person’s lifetime Some people are more likely to become infected and develop more severe illness than others due to genetic factors. – People of O blood group are at greatest risk for severe infection. Diagnosis l Norovirus can often be found in stool samples of infected persons by using special tests. – l l best made from stool specimens taken within 48 to 72 hours after onset of symptoms Blood tests looking for antibodies against norovirus are also performed, when the stool tests are inconclusive or were not done. Sequencing of noroviruses found in clinical samples has helped in conducting epidemiologic investigations by linking cases to each other and to a common source and by differentiating outbreaks that were mistakenly connected. Treatment l l l l No antiviral medication that works against norovirus No vaccine to prevent infection Norovirus infection cannot be treated with antibiotics. Treatment is supportive with fluids for dehydration (oral or intravenous) Prognosis l l l l l Usually not serious, although people may feel very sick and vomit many times a day Most people get better within 1 or 2 days No long-term health effects related to their illness. Can become dehydrated and may need medical attention No evidence to suggest that an infected person can become a long-term carrier of norovirus. Prevention l Resistant to environmental challenge. – They are able to survive freezing, and temperatures as high as 60°C, – Have even been associated with illness after being steamed in shellfish. – Can survive in up to 10 ppm chlorine, well in excess of levels routinely present in public water systems. Prevention l l l l l Frequently wash your hands, especially after toilet visits and changing diapers and before eating or preparing food. Carefully wash fruits and vegetables, and steam oysters before eating them. Thoroughly clean and disinfect contaminated surfaces immediately after an episode of illness by using a bleach-based household cleaner. Immediately remove and wash clothing or linens that may be contaminated with virus after an episode of illness (use hot water and soap). Flush or discard any vomitus and/or stool in the toilet and make sure that the surrounding area is kept clean. Prevention (Food Handlers) l l l Persons who are infected with norovirus should not prepare food while they have symptoms and for 3 days after they recover from their illness Food and drinks can very easily become contaminated with norovirus because the virus is so small and because it probably takes fewer than 100 norovirus particles to make a person sick Some foods can be contaminated with norovirus before being delivered to a restaurant or store. – – Several outbreaks have been caused by the consumption of oysters harvested from contaminated waters. Other produce such as salads and frozen fruit may also be contaminated at source. Surveillance l l l CDC currently does not conduct active surveillance to monitor outbreaks of gastroenteritis caused by noroviruses. Outbreaks are reported to CDC’s Viral Gastroenteritis Section, Respiratory and Enteric Viruses Branch, Division of Viral and Rickettsial Diseases, National Center for Infectious Diseases (NCID) CaliciNet is a database of norovirus sequences identified from outbreaks of norovirus that can then help to determine links between outbreaks. Cruise Ship Outbreaks l CDC investigated 21 reports of gastroenteritis aboard 17 cruise ships beginning January 1 through December 2, 2002. – – – l 9 were confirmed to be associated with noroviruses 3 were attributable to bacterial agents 9 were unknown etiology For comparison, in 2002, CDC confirmed 26 landbased outbreaks of gastroenteritis attributable to norovirus Vessel Sanitation Program l l Currently, over 140 cruise ships participate in the program. The inspection focuses on the following: – – – – – – – l l The ship's water supply The ship's spas and pools The ship's food The potential for contamination of food and water The practices and personal hygiene of employees The general cleanliness and physical condition of the ship The ship's training programs in general environmental and public health practices Inspection scores and reports are published on the VSP website www2.cdc.gov/nceh/vsp/vspmain.asp. Scores are also published every month in the Summary of Sanitation Inspections of International Cruise Ships, commonly referred to as the green sheet.