There are very few ways to entirely eliminate norovirus. Alcohol-based hand sanitizers, used by a number of cruise lines and recommended by hospital-based practices, need a minimum of 15-30 seconds of contact time to be effective and should not be considered a substitute for aggressive handwashing and mechanical drying. In addition, sanitizing the finger tips and under the finger nails with alcohol hand gels is difficult, and this may be another factor in their relative ineffectiveness in comparison to handwashing with soap and water. Because norovirus is an unencapsulated virus, alcohol-containing products are less effective and require higher concentrations of alcohol. Several popular commercially available products containing 62-70% alcohol demonstrate varying results, on average a log reduction between 2 and 4. Testing methodology and surrogates vary among the studies.
Alcohol-based hand gels are relatively ineffective in the disinfection and/or removal of norovirus from the hands. The recent increase in norovirus infection in acute care hospitals may be the result of the increased availability of alcohol-based hand gels, and the possible resultant reduction in the frequency of staff handwashing with soap and water and drying with a paper towel.
During an outbreak on board a cruise ship, most surfaces that can be safely disinfected are treated with sodium hypochlorite (bleach), with a concentration of 1000 ppm, freshly constituted (higher concentrations quoted are not freshly constituted and may have varying efficacy). A 1-minute contact time is required, and a >4.0 log reduction is anticipated. However, this concentration is not approved for food handling surfaces and cannot be used on fabrics and many other surfaces.
Steam cleaning to >70o C is recommended for carpets and certain furnishings.
Benzethonium chloride is a synthetic quaternary ammonium, surfactant, antiseptic, and anti-infective compound used as a topical antimicrobial agent and in antibacterial moist towelettes and wipes. While many of these compounds have limited efficacy for unencapsulated viruses, newer products seem more effective. However, studies show a contact time of >10 minutes may be required.
Accelerated and stabilized hydrogen peroxide is another product used for virucidal disinfecting. It requires a 5-minute contact time. It can be expensive, and, currently, no hand wipes are available.
Phenolic-based products have been used with some success in the past, but concerns about toxicity and their mucosal irritation when "fogged" have meant most cruise lines have moved away from their primary use in mitigating norovirus.
Oil of thyme, which has bactericidal and virucidal properties, is another hand wipe alternative.
Numerous new products are always becoming available, and objective third-party evaluations are critical in the decision-making processes.
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Hektoen enteric agar with Escherichia coli colonies. Different growth media are necessary for identifying different enteric pathogens, suppressing the growth of nonpathogens, and allowing for chemical reactions to assist in identification. The appearance results from the organism's ability to ferment lactose placed in the medium. This results in the production of acid, which lowers the pH and causes a change in the pH indicator placed in the medium. Salmonella and Shigella organisms do not ferment lactose.
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Example of Salmonella on Hektoen enteric agar. The medium also contains ferric ammonium citrate, which indicates the production of hydrogen sulfide by the appearance of a black precipitate.
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The MacConkey medium is commonly used and differentiates lactose fermenters, which produce acid, decrease the pH, and cause the neutral red indicator to give the colonies a pink-to-red color.
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The Christensen method is used to determine if an organism produces the enzyme urease (Yersinia) or not (Salmonella, Shigella, Vibrio). Hydrolysis of urea produces ammonia and carbon dioxide, alkalinizing the medium and turning the phenol red from light orange to magenta (pink).
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Often, a combination of methods may be used for identification. The tube on the left is triple sugar iron (TSI) agar. The alkaline slant and acid butt (K/A) indicates an organism that ferments glucose only (not lactose or sucrose). The middle tube is indole positive, as indicated by the pink ring, and indicates the organism's ability to split tryptophan to form indole. The tube on the right is urease negative. Taken together, these tests indicate the organism is likely Shigella.
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Gram stain may be helpful in identifying an etiologic agent. This stain shows gram-negative bacilli, which could be Salmonella or Shigella with 2 polymorphonucleocyte cells (PMNs).
