From the Guidelines
When suspecting norovirus infection, the most appropriate diagnostic test is a reverse transcription-polymerase chain reaction (RT-PCR) test performed on a stool sample, as it is considered the gold standard due to its high sensitivity and specificity 1. This molecular test directly detects viral RNA and is preferred over other methods such as enzyme immunoassays (EIAs) that detect norovirus antigens in stool, which are less sensitive than PCR.
Key Considerations for Testing
- Stool samples should be collected during the acute phase of illness, ideally within the first 48-72 hours of symptom onset when viral shedding is highest.
- Whole stool specimens are preferred over rectal swabs because of the higher quantity of virus present in whole stool 1.
- Vomitus may also be collected and tested using molecular assays, although the sensitivity of these assays for vomitus is unknown.
- Each specimen should be accompanied with dates of symptom onset and specimen collection to aid in interpretation.
Importance of Testing
Testing is particularly important in healthcare settings, for immunocompromised patients, or during suspected outbreaks to guide infection control measures and public health responses. In outbreak settings, testing just a few affected individuals is usually sufficient to confirm norovirus as the causative agent. Most cases of norovirus are diagnosed clinically based on characteristic symptoms (sudden onset of vomiting, watery diarrhea, abdominal cramps, and sometimes low-grade fever) and epidemiological factors, as routine testing is not always necessary for individual cases.
From the Research
Diagnostic Tests for Norovirus
When suspecting norovirus, several diagnostic tests can be used, including:
- Real-time reverse transcription polymerase chain reaction (RT-PCR) 2, 3, 4
- Enzyme immunoassays (EIA) 2, 4
- Immunochromatographic tests, such as RIDA®QUICK Norovirus 2
- Direct RT-PCR without RNA purification 5
Characteristics of Diagnostic Tests
The characteristics of these tests vary:
- Real-time RT-PCR is considered a highly sensitive and specific method for detecting norovirus 3, 4
- Immunochromatographic tests, such as RIDA®QUICK Norovirus, are easy to perform and read, but may have lower sensitivity compared to RT-PCR 2
- EIA has reduced sensitivity and specificity compared to real-time RT-PCR 4
- Direct RT-PCR without RNA purification is a simple and sensitive method for detecting norovirus 5
Recommendations for Testing
Based on the available evidence:
- Real-time RT-PCR is a recommended method for detecting norovirus due to its high sensitivity and specificity 3, 4
- Immunochromatographic tests, such as RIDA®QUICK Norovirus, may be useful for quick screening, but a negative result should be followed up by RT-PCR 2
- EIA may not be the best choice due to its reduced sensitivity and specificity compared to real-time RT-PCR 4
- Direct RT-PCR without RNA purification may be a viable option for detecting norovirus, especially in resource-limited settings 5