Norovirus infection laboratory findings
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Laboratory findings of norovirus infection include elevated concentration of inflammatory markers, hypokalemia, and chloride-sensitive metabolic alkalosis. Signs of dehydration may be present, such as relative polycythemia, elevated BUN, and elevated creatinine (pre-renal acute kidney injury). RT-PCR assay is the optimal test for the diagnosis of norovirus infection. Enzyme immunoassays to detect norovirus have been developed but are less useful due to low sensitivity. Norovirus is not usually grown on culture.
Laboratory Findings
- Lab findings of norovirus infection are usually related to the degree of dehydration. Lab findings include:[1][2]
- WBC count may be normal or elevated
- Elevated concentration of inflammatory markers (e.g. CRP or ESR)
- Chloride-sensitive metabolic alkalosis and electrolyte derangement (commonly hypokalemia)
- Relative polycythemia
- Elevated concentration of BUN
- Elevated creatinine is suggestive of pre-renal acute kidney injury in severe dehydration
Diagnostic Methods
The following methods is used for diagnosis of norovirus infection. [3][4][5]
RT-PCR Assays
- RT-PCR assays are the preferred laboratory method for detecting norovirus.
- 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-PCR 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.[6]
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.[6]
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.
- Samples that test negative should be confirmed by a second technique, such as RT-PCR.
- EIA kits should not replace molecular methods during outbreak investigations.[6]
Culture
- Human noroviruses cannot be grown in cell culture.
- Diagnostic methods focus on detecting viral RNA or antigen.[6]
Specimen Collection
Specimen collection for norovirus is carried out as explained below.[7][8]
Clinical Specimens
- Stool: Whole stool is that 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 within the greatest amount during this point. Norovirus can sometimes be detected in stool specimens that are collected later within 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 finished within 2 to three weeks. If the specimens are shipped to a laboratory for testing, each sample should be sealed in a very separate bag, and kept on frozen refrigerant packs in an insulated, waterproof polystyrene container. If testing are done over 3 weeks after the specimens are collected, they must be frozen at -4°F (-20°C) or -94°F (-70°C). When the specimens are stored during this way, norovirus is detected after a minimum of 5 years.
- Vomitus: 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: Serum specimens are not recommended for routine laboratory diagnosis of norovirus. 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, Water, and Environmental Specimens
- Food and Water Specimens: In theory, norovirus will be detected in water, food, and environmental specimens. However, the virus first has to be concentrated or extracted or both from the specimen. Validated methods for these techniques are available just for water (at CDC) and shellfish [at the seacoast Seafood Laboratory, Food and Drug Administration (FDA)]. If food or water are suspected to be contaminated, samples should be collected as soon as possible before people exposure. Food specimens should be stored frozen at -4°F (-20°C). Water will 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.
References
- ↑ Kawada J, Arai N, Nishimura N, Suzuki M, Ohta R, Ozaki T; et al. (2012). "Clinical characteristics of norovirus gastroenteritis among hospitalized children in Japan". Microbiol Immunol. 56 (11): 756–9. doi:10.1111/j.1348-0421.2012.00498.x. PMID 22889384.
- ↑ https://www.cdc.gov/norovirus/lab/index.html
- ↑ Rabenau HF, Stürmer M, Buxbaum S, Walczok A, Preiser W, Doerr HW (2003). "Laboratory diagnosis of norovirus: which method is the best?". Intervirology. 46 (4): 232–8. doi:10.1159/000072433. PMID 12931032.
- ↑ Marshall JA, Bruggink LD (2006). "Laboratory diagnosis of norovirus". Clin Lab. 52 (11–12): 571–81. PMID 17175887.
- ↑ Fisman DN, Greer AL, Brouhanski G, Drews SJ (2009). "Of gastro and the gold standard: evaluation and policy implications of norovirus test performance for outbreak detection". J Transl Med. 7: 23. doi:10.1186/1479-5876-7-23. PMC 2667494. PMID 19323808.
- ↑ 6.0 6.1 6.2 6.3 Centers for Disease Control and Prevention (2015). Norovirus: Diagnostic Methods. Accessed on December 8, 2015 http://www.cdc.gov/norovirus/lab-testing/diagnostic.html
- ↑ https://www.cdc.gov/norovirus/lab/specimen-collection.html
- ↑ Plantenga MS, Shiferaw B, Keene WE, Biggs C, Terry JM, Grenz L; et al. (2011). "Specimen collection and confirmation of norovirus outbreaks". Emerg Infect Dis. 17 (8): 1553–5. doi:10.3201/eid1708.101815. PMC 3381577. PMID 21801649.