What is Norovirus: Causes, Symptoms and Treatment
November 24, 2021
November 24, 2021
Another day, another virus and another outbreak. Scary, isn’t it? Not if we know all about it, the dos and don’ts, the must-have habits and everything we need to keep it under control. Learn about Norovirus and how is it turning into an epidemic?
Norovirus, also referred to as Norwalk viruses, is a group of highly contagious viruses that causes chronic gastroenteritis and other foodborne diseases. These are small, round, structured, non-enveloped viruses belonging to the Caliciviridae family. Norovirus causes extensive vomiting and diarrhoea. Globally, rotaviruses (RVs) followed by noroviruses (NoVs) are the most common causes of severe acute gastroenteritis (AGE) in children less than five years of age. Both diseases are characterised by vomiting and diarrhoea.
Studies show that Norovirus is the primary cause of AGE hospitalization in children. It is mostly in countries with the widespread use of the RV vaccine. However, in community-based studies, the clinical disease by Norovirus is milder than RV disease. It is because Norovirus also has different strains. Therefore, one can get affected multiple times by different strains.
Norovirus is classified into five groups GI-GIV. Though it can affect a broad spectrum of mammalian species, human noroviruses belong to GI, GII and GIV. GI and GII genomes cause the most infections. Severe infections can be fatal. Thus early detection is essential.
A myth around Norovirus is that it is “food poisoning,” “stomach flu,” or “stomach bug.” Although Norovirus is the leading cause of foodborne illness, other germs and chemicals can also cause foodborne illness. Remember, Norovirus is not related to the flu caused by the influenza virus.
Although the elderly and the younger ones are more likely to be infected, Norovirus can infect everyone. People who have a weak immune system are particularly more vulnerable to noroviruses. In addition, individuals with pre-existing medical conditions like diabetes and blood pressure issues are prone to severe infection.
Surveillance through collaborative networks like NoroNet and CaliciNet has provided vital insights into how different human norovirus strains correspond to outbreak settings and modes of transmission. For example, over the past 13 years, GII.4 genotype strain resulted in 70-80% of all reported cases. It means that the GII.4 strain is more responsible for person-to-person transmission than other transmission methods. At the same time, non-GII genotypes like GI.3, GI.6, GI.7, GII.12, GII.6 and GII.3 are associated with foodborne transmissions.
The surveillance also observed that genotype GI strain is more often linked with waterborne transmission than GII. It means that GI strains have higher stability in water.
To simplify the above, intake of infected food or water may result in infection after 12-72 hours. Contaminated water can also introduce the virus to your everyday water-based drinks, ice, vegetables, fruits, and sauces. Cooked foods may also be contaminated if handled by an infected individual. The virus quickly spreads when one comes into contact with infected individuals or from any surfaces they have touched recently.
Norovirus outbreaks have been reported in many areas. However, as per trends, the most common areas are Healthcare facilities. For example, half of all norovirus outbreaks in the US were from long term care facilities. Similarly, half the norovirus cases caused by food transmission in the US were from restaurants and catering events. The other two major outbreak areas were schools and cruise ships. It means that the various strains of Norovirus can spread through food, water, people carrying food or person-to-person contact. In addition, the readily contagious nature of the virus increases the risk of the outbreak turning into an epidemic.
The past year taught us a couple of things about immunity and the extent of damage a tiny virus can do. Norovirus causes inflammation in the stomach lining and intestine. The initial symptoms include:
Other common symptoms are:
Like Coronavirus, a real-time reverse transcription-polymerase chain reaction (RT-PCR) test helps detect Norovirus. The symptoms subside in 12 to 48 hours in a mild infection. However, the virus may spread through the faeces and vomit of the infected person for the next two weeks or more.
When we are finally getting used to the new normal, another virus outbreak has already made its way into the country. As per reports, 13 veterinary college students at Pookode in the Wayanad district of Kerala have been infected with Norovirus. The virus outbreak got noticed first among the students living in the hostel outside the campus.
As the norovirus spreads through contaminated water, food and surfaces, the chances of mass transmission among the students are likely. It happens mainly in a confined space like a dormitory or hostel.
As per reports, the officials have put the city of Mysuru on high alert after Norovirus’ outbreak in Kerala. The Health Department officials in border areas have decided to continue the screening for Covid-19 and Norovirus symptoms at the Bavali checkpoint until further orders from the district administration. In addition, an awareness drive has also been initiated to make people aware of the Norovirus.
Norovirus transmits by contaminated food, vomit, and person-to-person contact. The leading cause of non-bacterial acute gastroenteritis, Norovirus, is primarily characterised by a short incubation period, vomiting, nausea and diarrhoea. The illness is generally mild and self-limiting. However, diagnostic procedures aim to avoid nosocomial infections and unnecessary antibiotic treatment. Therefore, norovirus diagnosis depends on clinical suspicion in a patient with typical symptoms.
Primarily, Norovirus is diagnosed by detecting the virus in stool samples by transmission electron microscopy, polymerase chain reaction (PCR), or antigen ELISA. As per a study, PCR has the highest sensitivity (94.1%), followed by TEM (58.3%), and ELISA (31.3%), while specificity was highest for TEM (98.0%), followed by ELISA (94.9%), and PCR (92.4%).
All three methods tested (TEM, ELISA and PCR) are useful for epidemiological investigations in gastroenteritis outbreaks. However, to maximise diagnostic validity for individual cases, laboratories should combine at least two methods to maximise diagnostic validity for individual patients.
Currently, there are no vaccines available for norovirus. Although according to WHO, some vaccines are in the preclinical and human trial stage.
Norovirus is a viral infection and not bacterial. Therefore, antibacterial medications are ineffective against norovirus. The symptoms need treatment individually. Incorporating fluids in the diet keep the patient from dehydration. Hydration is an essential aspect of the treatment approach. As per reports, in severe cases, fluids are intravenously administered.
Since there is no definitive treatment, our best bet is to practice precautions.
Be watchful and aware of the outbreak. Becoming healthy enough to fight off the virus and adapting to the new normal are significant takeaways from the current scenario.