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Patogeni Emergenti: Norovirus

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Patogeni Emergenti: Norovirus
(Last Updated On: 13 agosto 2013)

 

Dalla prima pagina della crociera dei Norovirus molto tempo è passato ma soprattutto molto è stato fatto in termini informativi e preventivi dalle Istituzioni Internazionali. Tra le tossinfezioni alimentari sono entrate nel mirino di CDC e EDEC le epidemie da norovirus. Il motivo è presto detto: sono considerate la prima causa di enteriti nelle comunità e il gold standard della prevenzione è sempre il lavaggio delle mani. Il CDC ha dedicato un intero settore al problema con ampio spazio alla documentazione divulgativa (http://www.cdc.gov/hicpac/pdf/norovirus).

 Anche in europa con l’ECDC si è affrontato l’argomento con il tecnical report “Prevention of norovirus infection in schools and childcare facilities”.

Metodi Diagnostici sono basati su identificazione di RNA virale o antigeni (forniamo un report CDC based)

RT-qPCR Assays real-time reverse transcription-polymerase chain reaction (RT-qPCR) assays è il test d’elezione (These assays are very sensitive and can detect as few as 10 to 100 norovirus copies per reaction. They use different primers to differentiate genogroup I and genogroup II norovirus. RT-qPCR assays are also quantitative and can provide estimates of viral load. The assays may be used to detect norovirus in stool, vomitus, foods, water, and environmental specimens).

Conventional RT-PCR Assays for Genotyping Conventional RT-PCR followed by sequence analysis of the RT-PCR products is used for norovirus genotyping. Typically, a partial region of the capsid gene, such as region D, is used by laboratories participating in CaliciNet, a national laboratory surveillance network for norovirus outbreaks coordinated by CDC.

Enzyme Immunoassays Rapid commercial assays, such as enzyme immunoassays (EIAs), that detect norovirus antigen have recently been developed. However, these kits have poor sensitivity (50%) and are not recommended for diagnosing norovirus infection in sporadic cases of gastroenteritis. The RIDASCREEN Norovirus 3rd Generation EIA was recently cleared by Food and Drug Administration for preliminary identification of norovirus when testing multiple specimens during outbreaks. However, samples that test negative should be confirmed by a second technique, such as RT-qPCR. Thus, EIA kits should not replace molecular methods during outbreak investigations.

Stool Whole stool is the preferred clinical specimen for laboratory diagnosis of norovirus. Ideally, specimens should be collected during the acute phase of illness (within 48 to 72 hours after symptoms start) while stools are still liquid or semisolid. Virus is excreted in the greatest amount during this time. Norovirus can sometimes be detected in stool specimens that are collected later in the illness or after the symptoms have resolved (up to 7 to 10 days after onset). Whole stool specimens should be kept refrigerated at 39°F (4°C) if testing is done within 2 to 3 weeks. If the specimens are shipped to a laboratory for testing, each sample should be

  • sealed in a separate bag, and
  • kept on frozen refrigerant packs in an insulated, waterproof polystyrene container.

If testing will be done more than 3 weeks after the specimens are collected, they should be frozen at -4°F (-20°C) or -94°F (-70°C). When the specimens are stored in this way, norovirus can be detected after at least 5 years.

Vomitus: can be collected to supplement stool specimens during an investigation. These specimens should be collected, stored, and shipped in the same way as stool specimens.

Serum: specimens are not recommended for routine laboratory diagnosis of NV. If feasible and warranted for special studies, acute- and convalescent-phase serum specimens may be collected and tested for a greater than fourfold rise in IgG titer to noroviruses.

  • Acute-phase serum specimens should be collected during the first 5 days after the symptoms start.
  • Convalescent-phase specimens should be collected during the third to fourth week after the symptoms start.

Food and Water Specimens

  • In principle, norovirus can be detected in water, food, and environmental specimens. However, the virus first needs to be concentrated or extracted or both from the specimen. Validated methods for these techniques are available only for water (at CDC) and shellfish [at the Gulf Coast Seafood Laboratory, Food and Drug Administration (FDA)].
  • If food or water is the suspected cause of a norovirus outbreak, samples should be collected as soon as possible after people were exposed.
  • Food specimens should be stored frozen at -4°F (-20°C).
  •  Water can be tested for norovirus by processing large volumes (up to 100L) through specially designed filters. Water samples should be stored refrigerated or chilled on ice at 39°F (4°C).

Environmental Specimens

  • Norovirus RNA has been detected in swabs of environmental surfaces collected in specific outbreak settings. However, obtaining virus from swabs is highly variable. Results should be interpreted with caution and in the context of the available epidemiologic evidence.

All’estero i Norovirus sono quindi ampiamente monitorati, ma da noi?

   In allegato la Documentazione relativa in formato PDF

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Giovanni Casiraghi

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