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Norovirus cases detected in Kerala: what is this virus and how dangerous is it?

The virus is capable of surviving low temperatures, and outbreaks tend to be more common during the winter and in colder countries — that is why it is sometimes referred to as "winter vomiting disease".

Norovirus-ExplainedElectron microscopic image of norovirus virions (Source: Centers for Disease Control and Prevention)

The Kerala Health Department on Monday (January 24) confirmed two cases of the gastrointestinal infection norovirus in class 1 students in Ernakulam district. The two samples were tested after 62 persons — students and their parents — developed symptoms such as diarrhoea, abdominal pain, vomiting, nausea, a high temperature, headache, and body aches.

What is norovirus and how common are infections?

Norovirus is not new; it has been circulating among humans for over 50 years and is thought to be one of the primary causes of gastroenteritis. The virus is estimated to kill 200,000 persons globally every year, with most deaths occurring among those below the age of five years and those over the age of 65 years.

The virus is capable of surviving low temperatures, and outbreaks tend to be more common during the winter and in colder countries — that is why it is sometimes referred to as “winter vomiting disease”. The reported cases of norovirus had seen a decline in the United Kingdom during the pandemic, likely due to lax surveillance, but numbers have since picked up. A 48% higher incidence of reported cases than expected was reported by the UK Health Security Agency (UKHSA) in 2022.

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A 2022 study published in the peer reviewed journal Viruses says that norovirus infections are more frequently detected in high income countries, with almost 40% cases being seen in long-term care facilities. In contrast, the cases in India have mostly been detected in settings like schools and hostels, where people share food.

And what is the incidence of infection in India?

Cases of norovirus are not as common in India as in many other places — at the same time, the recent cases in Kerala are by no means unique or one-offs. The infection has been reported in previous years as well, mainly from Southern India, and especially from Kerala.

A 2016 study by Christian Medical College-Vellore that followed a birth cohort of 373 for three years, detected 1,856 diarrhoeal episodes and 147 vomiting episodes. The study said that norovirus was detected in 11.2% of the diarrhoeal episodes and 20.4% of the vomiting episodes.

A 2021 study from Hyderabad reported that norovirus was detected in 10.3% samples of children who came in with acute gastroenteritis.

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Dr E Sreekumar, director of the Institute of Advanced Virology-Kerala, said that the reported cases of norovirus have been on the rise in recent years. “One of the reasons could well be that we were not looking for the virus previously. Now we have systems to detect not just this virus but several others.”

Dr Sreekumar said his institute follows a syndromic approach to testing patient samples — making clinical decisions based on a patient’s symptoms and signs — rather than testing for one viral infection that the treating doctor might suspect.

“We have a panel for detecting 83 different viruses. Instead of testing for, say, just Covid-19 or flu, we will test for 12 viral infections that can cause respiratory symptoms. Or, if the physician says that a person has gastrointestinal symptoms, we will run a panel for six or seven viruses. That is how we end up picking up cases of norovirus,” Dr Sreekumar said.

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If institutes started doing genomic sequencing of the samples, more viruses were likely to be detected, he added.

But why is the infection so common in Kerala, especially?

It probably has more to do with Kerala’s strengths than any weaknesses. Dr Sreekumar said that the state has a strong public health system that is capable of picking up clusters of infection and getting them tested quickly.

Can norovirus infection cause a large-scale outbreak?

No. Even though more cases of norovirus are being detected, experts say that this is unlikely to lead to a large-scale outbreak.

“Although we haven’t studied the epidemiological co-relates of these cases, what we have seen is that the norovirus cases are sporadic and found in small clusters in schools or hostels where people consume the same foods. The spread of the infection is also self-limiting. It is an individual problem, not a public health one,” Dr Sreekumar said.

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What are the symptoms and how to prevent its spread?

Norovirus leads to diarrhoea, vomiting, nausea, and abdominal pain. Being a diarrhoeal disease, it can lead to dehydration, so drinking plenty of fluids is recommended.

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The infection can be transmitted through foods contaminated with the virus, touching surfaces that are contaminated with the virus and then touching the mouth, and being in direct contact with someone with the infection like taking care of them and sharing foods and utensils with them.

Good hand hygiene is the best way to prevent infection. Wash your hands with soap and water for 20 seconds. Hands sanitisers are thought to not work too well against norovirus.

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As the infection can be transmitted by foods, it is suggested that a sick person not prepare food for others. All food items should be carefully washed and cooked at high temperatures. The norovirus can survive temperatures as high as 60 degrees Celsius.

Areas where a sick person has vomited or had diarrhoea should be cleaned using disinfectants or bleach.

First published on: 24-01-2023 at 18:03 IST
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