Norovirus GI & GII, or Norwalk virus, is the most common cause of non-bacterial gastroenteritis in the world. It is widely known for causing the stomach flu on cruise ships. Three genotypes of this diverse virus, GI, GII, and GIV, can infect humans. Genotype group II, genotype 4 (GII.4) is the most common and accounts for the majority of outbreaks around the world. Norovirus, which can have a sudden or gradual onset, typically develops 24-48 hours after contact with an infected person or ingestion of contaminated food or water.
Norovirus, which can have a sudden or gradual onset, typically develops 24-48 hours after contact with an infected person or ingestion of contaminated food or water.
Norovirus is generally short-lived, lasting about 24-72 hours but it is highly contagious due to its stability in the environment and resistance to heat, cold, and disinfectant solutions. It can survive on hard surfaces for weeks and up to 12 days on contaminated fabrics. Infection affects the microvilli of the small intestine, not the colon. Those infected can spread the virus for up to two weeks after recovery. Noroviruses are the most common cause of sporadic diarrhea in community settings and cause up to half of all outbreaks of gastroenteritis.
Symptoms can include the following:
– Nausea and vomiting,
– Diarrhea,
– Abdominal cramps,
– Lowgrade fever,
– Muscle aches,
– Fatigue,
– And Headache.
Treatments for norovirus include hydration and electrolytes primarily, and in some cases antiemetic drugs for nausea and vomiting, and analgesics for pain and headache. Intravenous fluid and electrolytes may be needed in extreme cases. PCR is a highly sensitive and specific method for detection of norovirus.
Source: Norovirus GI/II – Lab Results explained | HealthMatters.io
RT-qPCR Assays
RT-qPCR assays are the preferred method to detect norovirus. RT-qPCR assays are very sensitive and specific. They can detect as few as 10 to 100 norovirus copies. They use different oligonucleotide primer sets to detect genogroup I, genogroup II, genogroup VIII and GIX noroviruses. RT-qPCR assays can also provide estimates of viral load.
TaqMan-based RT-qPCR assays detect the RNA of the virus. They can be used to test the following for norovirus:
Recently, several commercial platforms for detection of multiple gastrointestinal pathogens have become available. They include genogroup I and genogroup II norovirus. The sensitivity of these assays for norovirus is in the same range as RT-qPCR.
Rapid commercial enzyme immunoassays (EIAs) that detect norovirus antigen in stool samples are also available. However, these kits have poor sensitivity (50% to 75%) and are generally not recommended for testing single samples from sporadic cases of gastroenteritis.
These assays can be used for preliminary identification of norovirus when testing multiple specimens during outbreaks. However, samples that test negative should be confirmed by a second technique, such as RT-qPCR. Thus, EIA kits should not replace RT-qPCR during outbreak investigations.
Genetic characterization of noroviruses detected in stool and environmental samples can be very useful in epidemiologic investigations by:
Norovirus can be genotyped by sequence analysis of a RT-PCR product amplified from a partial region of both the polymerase gene (region B) and capsid gene (region C) in a single reaction for either genogroup I or genogroup II viruses.
All laboratories participating in CaliciNet use dual typing for norovirus. The sequences obtained are compared to CaliciNet reference sequences for typing. An example of dual typing nomenclature is the GII.4 Sydney[P16] norovirus strain; it has caused the majority of all norovirus outbreaks in the United States in recent years.
Healthcare providers should report all outbreaks of acute gastroenteritis, including suspected outbreaks of norovirus, to the appropriate health department.
Health departments are encouraged to report all suspected and confirmed norovirus outbreaks through the National Outbreak Reporting System (NORS) and CaliciNet.
Norovirus Reporting and Surveillance
