Specimens for norovirus testing may be:
- Whole stool or stool
- Cary Blair medium
Whole stool is the preferred clinical specimen for laboratory diagnosis of norovirus illness. During outbreak investigations, specimens should be collected from at least 5 ill people. Ideally, stool specimens should be collected during the acute phase of illness (up to 72 hours after symptoms start) while the stool is still liquid or semisolid. The greatest amount of virus is shed during the acute phase of illness.
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). The number of specimens collected should be increased if collected after the acute phase of illness or for large or protracted outbreaks.
If the specimens are shipped to a laboratory for testing, each sample should be:
- Clearly labelled with a unique identifier (such as specimen ID),
- Placed in a leak-proof plastic container and sealed in a separate bag, and
- Kept on frozen refrigerant packs in an insulated, waterproof polystyrene container.
If testing occurs within 2 to 3 days from collection for whole stool and Cary-Blair specimens, and within 2 to 3 weeks for stool specimens, samples should be refrigerated at 39°F (4°C). If testing occurs beyond these times or are to be archived, samples should be frozen ideally at -94°F (-70°C) or at -4°F (-20°C) if storage at -94°F (-70°C) is not available.
Vomitus can be collected in addition to stool specimens during an outbreak investigation. These specimens should be collected and shipped in the same way as stool specimens. Vomitus samples should always be stored frozen at -4°F (-20°C) or at -94°F (-70°C).
Serum specimens are not recommended for routine laboratory diagnosis of norovirus illness.
If feasible and warranted for special studies, acute (symptoms showing) and convalescent (recovering from symptoms)-phase serum specimens may be collected and tested for a greater than four-fold rise in IgG titer to noroviruses. Serum samples should be stored frozen at -4°F (-20°C).
- 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.
For more information on specimen collection, see 2011 MMWR: Updated Norovirus Outbreak Management and Disease Prevention Guidelines.
Food, Water, and Environmental Specimens
In principle, norovirus can be detected in water, food, and environmental specimens. However, the virus first needs to be concentrated and/or extracted from the water or food specimen. Validated methods for these techniques are available at CDC for clean water and for surface water and at U.S. Food and Drug Administration (FDA) for several food commodities including shellfish, leafy greens, and berries. Food samples 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).
If food or water is the suspected cause of a norovirus outbreak, samples should be collected as soon as possible after people were exposed and immediately refrigerated. For more information on reporting waterborne or foodborne illnesses, see CDC Waterborne Disease and Outbreak Surveillance Reporting or How to report a foodborne illness.
Swabs of objects, such as doorknobs and handrails, and hard surfaces, such as kitchen counters, can also be tested for norovirus. However, the amount of virus on surfaces is often low and detection of virus from swabs is not always possible. For information about swabbing and processing samples in the laboratory, see Swab Sampling Method for the Detection of Human Norovirus on Surfaces. Results should be interpreted with caution and in the context of the available epidemiologic evidence.
Selected resources from state health departments
- How to Collect a Stool Specimen for the Health Department
- How to Collect Your Poop for the Health Department
References for recovering microbes from water:
- Hill VR, Mull B, Jothikumar N. et al. Detection of GI and GII Noroviruses in Ground Water Using Ultrafiltration and TaqMan Real-time RT-PCR. Food Environ Virol 2, 218–224 (2010).
- Mull B, Hill VR. Recovery of diverse microbes in high turbidity surface water samples using dead-end ultrafiltration. J Microbiol Methods. 2012;91(3):429-433.
References for detection of norovirus in food, Food and Drug Administration (FDA):
- Bacteriological Analytical Manual (BAM), Chapter 26: Detection and Quantitation of Hepatitis A Virus in Shellfish by the Polymerase Chain Reaction
- Bacteriological Analytical Manual (BAM), Chapter 26B: Detection of Hepatitis A Virus in Foods
- Sampling and Testing Method Guidance for the Detection of Norovirus and Hepatitis A Virus in Soft Fruit
References for environmental sampling:
- Park, GW, Chhabra, P, Vinjé, J. Swab Sampling Method for the Detection of Human Norovirus on Surfaces. Vis. Exp.2017;(120):55205. doi:10.3791/55205