Update September 2008
The condition: The acute gastroenteritis (“gastro”) of adults is usually caused by members of the small, round, Norwalk-like virus (“NLV”) group (= Norovirus) of the Caliciviridae family. After an incubation of 12-60 h, typical symptoms are nausea, projectile vomiting and diarrhoea lasting for 25-72 h. When administered to volunteers, 82% become infected and 68% show symptoms. Faecal virus shedding lasts for up to two weeks (considerably longer than traditionally advised). Viral content in vomit and stool is high, being about 106/mL. With fewer than 100 viral particles needed for infection, it is highly infectious.
Initial Infection: This is usually by faecal-oral transmission through contaminated water, foods (especially cold, hand-prepared foods such as sandwiches, deli ham and salads), also vomit droplets, and body contact (as between North American footballers).
Environmental spread: In an Hotel setting with an ongoing outbreak, spread was assumed to be from dispersed virus in the environment. Two carpet categories sampled were 75% and 62% virus positive early in the outbreak. Toilet rims &/or seats were 73% positive, supported by a later study. Since direct skin contact is with toilet seats and not with carpet, the former may be the more important for the spread.
When a dye was placed in a toilet bowl and the toilet flushed, the dye appeared on the upper seat surface, indicating the potential for raw sewage to contaminate the skin contact surface. This result may be influenced by water pressure, design, bowl content and chance. There is a risk for direct skin transfer.
Cleaning & Disinfection: Dry NLV survival may be up to 28 days. Cleaning of carpets etc. with detergent and subsequent vacuum cleaning is considered inadequate. Traditional surface disinfection is with strong oxidizing solutions, such are sodium hypochlorite (which releases chlorine, for which NLV may have resistance, and that some find unpleasant) and peroxide (which releases oxygen, is colourless and odourless). Quaternary ammonium compounds (“Quats”) can kill some viruses, but not the Norwalk group. Cleaning with Quats may disperse the virus and place the cleaner at risk. Heat, as by cooking of oysters, is unreliable. Steam cleaning of carpets is suggested.
Prevention: The faecal/vomit-to-oral route must be broken. Hand washing by food preparation staff is obligatory (+/- alcoholic/disinfectant handrub) and intact gloves should be worn. Areas contaminated by faecal material and vomit must be adequately cleaned and disinfected, with the cleaners using gloves, aprons and masks.
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