In cases involving a norovirus, diagnosis usually involves a physical exam and a review of the patient's medical history and symptoms. In most cases, the doctor can only diagnose a person with what is commonly called "stomach flu." There is no routine lab test used to make a norovirus diagnosis. Special tests used to identify a norovirus infection are usually only used when there is an outbreak and the specific virus causing it needs to be identified.
In order to make a norovirus diagnosis, the doctor will ask a number of questions about a person's medical history, including questions about:
- Current medical conditions
- Current medications
- Family history of any medical conditions
- Recent travel history
- Recent food and liquid consumption.
The doctor will also likely perform a physical exam, looking for signs and symptoms of norovirus.
In most cases, based on the medical history and the physical exam, the doctor will make a diagnosis of viral gastroenteritis (also known as the "stomach flu"), but will not be able to say specifically whether a norovirus infection is causing the gastroenteritis symptoms. This is because there is no routine lab test to detect norovirus.
In special cases, for example, when there is an outbreak of gastroenteritis, there is a need to identify norovirus as the cause of the illness. In these cases, norovirus can often be found in stool samples of infected persons by using special tests. Sometimes, blood tests that check for norovirus antibodies are also performed when the stool tests are inconclusive or were not done. Food handlers will often be asked for a stool sample, or even a blood sample, to help investigate the cause of an outbreak.