Test Catalog

Test Id : LNORO

Norovirus PCR, Molecular Detection, Feces

Useful For
Suggests clinical disorders or settings where the test may be helpful

Diagnosing gastrointestinal disease (diarrhea or vomiting) caused by norovirus genogroups 1 and 2


This test should not be used as a test-of-cure.

Method Name
A short description of the method used to perform the test

Real-Time Polymerase Chain Reaction (PCR)/RNA Probe Hybridization

NY State Available
Indicates the status of NY State approval and if the test is orderable for NY State clients.


Reporting Name
Lists a shorter or abbreviated version of the Published Name for a test

Norovirus PCR, F

Lists additional common names for a test, as an aid in searching

Norwalk Virus

Specimen Type
Describes the specimen type validated for testing


Shipping Instructions

Place vial in a sealed plastic bag and ship ambient. Specimens received at other temperatures will be rejected, and testing will be canceled.

Specimen Required
Defines the optimal specimen required to perform the test and the preferred volume to complete testing

Supplies: Culture and Sensitivity Stool Transport Vial (T058)

Container/Tube: Commercially available transport system specific for recovery of enteric pathogens from fecal specimens (15 mL of non-nutritive transport medium - either Cary-Blair, Para-Pak Culture and Sensitivity Media)

Specimen Volume: Representative portion of diarrheal fecal sample, 1 gram or 5 mL

Collection Instructions:

1. Collect fresh feces and place in preservative within 1 hour of collection.

2. Visibly formed feces are not consistent with Norovirus gastrointestinal disease and should not be submitted for testing.

Reject Due To
Identifies specimen types and conditions that may cause the specimen to be rejected

Nonpreserved feces
Transport media other than Cary-Blair or C and S
Modified Cary-Blair
Fecal swabs
Visibly formed feces

Specimen Stability Information
Provides a description of the temperatures required to transport a specimen to the performing laboratory, alternate acceptable temperatures are also included

Specimen Type Temperature Time Special Container
Fecal Ambient 7 days

Useful For
Suggests clinical disorders or settings where the test may be helpful

Diagnosing gastrointestinal disease (diarrhea or vomiting) caused by norovirus genogroups 1 and 2


This test should not be used as a test-of-cure.

Clinical Information
Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Noroviruses, previously known as Norwalk-like viruses, are highly contagious RNA viruses that cause acute gastroenteritis (diarrhea, vomiting). Although 6 genogroups of norovirus have been identified, only 3 genogroups (genogroup: G1, G2, and G4) cause disease in humans. Furthermore, the majority of outbreaks have been associated with G1 and G2, with G2 being most common.(1)


Noroviruses are transmitted through close, personal contact with an infected individual or via the fecal-oral route in which the virus becomes ingested in contaminated food or water. These viruses are extremely contagious, with fewer than 20 virions being able to cause disease.(1)


Once infected, the incubation period is typically short, between 24 and 72 hours. The onset of symptoms is abrupt, with vomiting and watery nonbloody diarrhea being common. Patients may also experience a low-grade fever, as well as headache and mild body aches.(1)


The diagnosis of norovirus infection can often be made on clinical grounds, and symptoms generally resolve in 24 to 48 hours. However, in certain patients, especially those who are immunocompromised or hospitalized, laboratory testing may be indicated for infection control purposes and to limit the use of antibiotics. Testing of diarrheal feces by real-time polymerase chain reaction allows for a rapid and sensitive means of detecting and differentiating norovirus G1 and G2 in clinical stool samples.

Reference Values
Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.


Provides information to assist in interpretation of the test results

A positive result indicates that RNA from norovirus genogroups 1 and/or 2 was present in the clinical specimen.


A negative result suggests that RNA from norovirus genogroups 1 and 2 was absent in the clinical specimen.

Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

A positive result suggests that norovirus is the cause of gastrointestinal disease (diarrhea or vomiting); however, in certain patients (eg, immunocompromised hosts), norovirus may be shed for weeks to months in the absence of symptoms.(2)


This test should not be used as a test-of-cure, due to the fact that norovirus nucleic acid may be detected in patients for weeks to months following the resolution of symptoms.(2)


A negative result suggests that norovirus is not the cause of gastrointestinal disease (diarrhea or vomiting); however, viral nucleic acid may be present at a level that is below the limit of detection for this test. The results should be interpreted in the context of the patient's clinical presentation and other laboratory findings.

Supportive Data


A total of 100 clinical stool specimens submitted to Mayo between 11/2015 and 03/2016 for testing by a commercial multiplex gastrointestinal panel (that includes norovirus) were aliquoted, blinded, and tested within 24 to 48 hours of receipt using the norovirus G1/G2 real-time polymerase chain reaction (PCR) assays. Specimens yielding discordant results between the multiplex panel and the real-time PCR were submitted to an outside reference lab and the Minnesota Department of Health (MDH) for norovirus molecular testing.


Table 1. Comparison of results following discordant analysis at an outside reference laboratory and MDH



Number of samples following discordant resolution with a result of: (a,b)

Norovirus lab-developed test (LDT)













Adjusted Sensitivity (95% confidence interval [CI])=96.9% (88.8, 99.8)

Adjusted Specificity (95% CI)=100% (88.2, 100)

Adjusted Agreement (95% CI)=98% (92.6, 99.9)


a. Samples showing discordant results between the norovirus real-time PCR and FilmArray were tested by a molecular method at Focus Diagnostics and MDH.

b. Samples that showed agreement between the norovirus real-time PCR and FilmArray were not tested further.

c. Four of these 63 samples were identified as G1 by the LDT; the remaining 59 were identified as norovirus G2.

d. One of these 2 samples was positive for norovirus at Focus Diagnostics and MDH, and upon repeat testing in triplicate by the LDT, was also positive. The second sample was positive for norovirus at MDH, but negative by Focus and the LDT upon repeat testing.


Testing of clinical stool samples yielded 59 specimens that were positive for norovirus G2 by the LDT; however, only 4 samples were determined to be positive for norovirus G1. In order to supplement the clinical data and increase the number of samples positive for norovirus G1, spiking studies were performed. Analyte-negative stool samples (n=26) were spiked with norovirus G1 RNA (ATCC) at 1 dilution above the defined limit of detection (LOD) (Table 2).


Table 2. Results of spiking studies for norovirus GI in stool specimens.




Concentration of target in spiked sample

Number positive/
number tested

% Positive

Mean crossing point


Norovirus G1

10 copies/mcL





Analytical Sensitivity:

The limit of detection of both the G1 and G2 assays was determined to be 5 copies/mcL (5000 copies/mL) of stool.


Analytical Specificity:

A comprehensive specificity panel, consisting of bacteria (n=16), parasites (n=5), or viruses (n=5) known to cause gastrointestinal disease was tested by the norovirus G1/G2 assays. In addition, human DNA was tested. All members of the specificity panel were negative by both the norovirus G1 and G2 assays. In addition, a BLAST (basic local alignment search tool) analysis was performed on the primer and probe sequences and did not reveal significant cross-reactivity with organisms that may be present in stool samples.

Clinical Reference
Recommendations for in-depth reading of a clinical nature

1. National Center for Immunization and Respiratory Diseases, Division of Viral Diseases: Norovirus. Center for Disease Control and Prevention; 2013. Updated February 23, 2023. Accessed March 28, 2023. Available at www.cdc.gov/norovirus/index.html

2. Echenique IA, Stosor V, Gallon L, Kaufman D, Qi C, Zembower TR: Prolonged norovirus infection after pancreas transplantation: a case report and review of chronic norovirus. Transpl Infect Dis. 2016 Feb;18(1):98-104

Method Description
Describes how the test is performed and provides a method-specific reference

This assay utilizes real-time, TaqMan-based polymerase chain reaction (PCR) technology to target the nonstructural polyprotein gene of norovirus G1 and G2. Nucleic acid is extracted from diarrheal stool samples in Cary-Blair media. Following extraction of viral RNA, reverse transcription is performed to convert norovirus genomic RNA to complementary DNA. Real-time amplification and detection are then performed. Two separate real-time PCR reactions are performed for each sample, one specific for norovirus G1 and the second targeting norovirus G2. The assay is able to accurately detect and differentiate these genogroups in clinical stool samples.(Unpublished Mayo method)

PDF Report
Indicates whether the report includes an additional document with charts, images or other enriched information


Day(s) Performed
Outlines the days the test is performed. This field reflects the day that the sample must be in the testing laboratory to begin the testing process and includes any specimen preparation and processing time before the test is performed. Some tests are listed as continuously performed, which means that assays are performed multiple times during the day.

Monday through Friday

Report Available
The interval of time (receipt of sample at Mayo Clinic Laboratories to results available) taking into account standard setup days and weekends. The first day is the time that it typically takes for a result to be available. The last day is the time it might take, accounting for any necessary repeated testing.

2 to 5 days

Specimen Retention Time
Outlines the length of time after testing that a specimen is kept in the laboratory before it is discarded

7 days

Performing Laboratory Location
Indicates the location of the laboratory that performs the test


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Test Classification
Provides information regarding the medical device classification for laboratory test kits and reagents. Tests may be classified as cleared or approved by the US Food and Drug Administration (FDA) and used per manufacturer instructions, or as products that do not undergo full FDA review and approval, and are then labeled as an Analyte Specific Reagent (ASR) product.

This test was developed, and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the US Food and Drug Administration.

CPT Code Information
Provides guidance in determining the appropriate Current Procedural Terminology (CPT) code(s) information for each test or profile. The listed CPT codes reflect Mayo Clinic Laboratories interpretation of CPT coding requirements. It is the responsibility of each laboratory to determine correct CPT codes to use for billing.

CPT codes are provided by the performing laboratory.

87798 x 2

LOINC® Information
Provides guidance in determining the Logical Observation Identifiers Names and Codes (LOINC) values for the order and results codes of this test. LOINC values are provided by the performing laboratory.

Test Id Test Order Name Order LOINC Value
LNORO Norovirus PCR, F 88701-8
Result Id Test Result Name Result LOINC Value
Applies only to results expressed in units of measure originally reported by the performing laboratory. These values do not apply to results that are converted to other units of measure.
65170 Norovirus G1 PCR 54905-5
47553 Norovirus G2 PCR 54906-3

Test Setup Resources

Setup Files
Test setup information contains test file definition details to support order and result interfacing between Mayo Clinic Laboratories and your Laboratory Information System.

Excel | Pdf

Sample Reports
Normal and Abnormal sample reports are provided as references for report appearance.

Normal Reports | Abnormal Reports

SI Sample Reports
International System (SI) of Unit reports are provided for a limited number of tests. These reports are intended for international account use and are only available through MayoLINK accounts that have been defined to receive them.

SI Normal Reports | SI Abnormal Reports