MFF0089: Norovirus and norovirus infection


Hello and welcome to the Medical Fun Facts Podcast

This is episode 89 and it is Monday 23 October 2017

Hit the play button to listen

Tonight, I’m talking about Norovirus and norovirus infection. I’m guessing some listeners will have had first hand or second-hand knowledge of this illness. It’s really common and it can sweep through a close community really rapidly.

So, what is norovirus?

The norovirus is a very small RNA virus, it’s usually described as being about 27 nanometres in diameter. That is tiny. When you consider rotavirus is about 80 nanometres and variola virus which causes smallpox is up to 350 × 250 nanometres. Norovirus is on par with poliovirus which is about 30 nanometres in diameter.

Norovirus sits in the family Caliciviridæ which should not be confused with the word Khaleesi from the novel and TV production Game of Thrones. Where Khaleesi means the wife of the Khal. Where Khal is the Dothraki word for the warlord or commander of tens of thousands of warriors and support people. Sorry, you can tell I’m a fan of Game of Thrones.

Clinical

Infection with norovirus is usually self-limiting and mild but occasionally it can be a moderate in the sense it can be incapacitating for some patients. Infection is often associated with outbreaks in schools, child-care centres, residential aged care facilities, hospitals and on cruise ships. The usual clinical symptoms include fever, vomiting and diarrhoea. Other symptoms associated with infection include a headache, malaise, and some muscle pain along with abdominal discomfort.

Diagnosis

The diagnosis of norovirus infection in this day and age can be made with PCR but back when I was a boy, electron microscopy was occasionally used. Then there were some immunoassays were developed but those tests were never really good. Today, we can use multiplex PCR for stool specimens so that we can potentially identify the common bacterial and viral pathogens in a single stool specimen quickly and easily.

Transmission

On the subject of cruise ships, I often think of them as floating buckets of vomit and faeces. It’s so common to read reports of nasty outbreaks of influenza, rotavirus infection and norovirus infection on them. I know the management of the cruise line companies and the crew on each ship go to great lengths to encourage a safe and infection-free voyage, however, all it takes is one passenger to board with an active infection and a small breakdown in infection prevention and control measures can result in huge problems. Can you imagine being on a big boat and feeling seasick and also have passengers around you who are heaving their guts out and then developing explosive diarrhoea? What a great combination. Clearly, this podcast is not sponsored by any cruise line companies. In fact, the podcast has no sponsors at all.

When you think of all the cases of sporadic gastroenteritis in the world, norovirus infection can make up to between 9 and 24 per cent of all cases. Norovirus infection can affect all ages but is worse in the very young and very old.

Humans are the only known reservoir. The infection tends to cause pathology of the mucosal epithelium of the small intestine. The epithelial cells are not killed but damaged. Norovirus infection does not result in dysentery, i.e., blood, pus and lots of mucus in the stools.

Think about all the other infectious diseases I’ve mentioned on this podcast and think about the incubation periods. Most of the time, for most infectious diseases, the incubation period is measured in days, but for norovirus infection, it is measured in hours. It can be as little as 10 to 50 hours.

Norovirus infection is usually transmitted via the faecal-oral route which can be directly between humans or indirectly via food, water or surfaces. In some situations, if the vomit is aerosolised, an infection can be transmitted when aerosolised vomit gets in your mouth. Think about caring Mums and Dads holding sick children and getting some vomit in their faces. Norovirus can easily contaminate shellfish like oysters via contaminated water. When the contaminated shellfish are eaten, infection follows quickly.

Patients are most likely to share the infection in the early stages of the disease; however, norovirus can be found in a patient’s faeces for up to 2 to 3 weeks after the symptoms resolve. Symptoms normally last only between 1 and 3 days.

Risk groups include as I mentioned, humans >65 and <5 years as well as anyone who is immunocompromised.

Management

Patients are managed by getting them to rest and remain hydrated. It’s important not to spend time with others so isolate yourself so you don’t risk sharing the infection. Hand washing is really important especially after using the toilet for either voiding urine or opening your bowels. Don’t shake someone else’s hand and if you find yourself in the midst of an outbreak, don’t shake hands, always wash your hands before touching your mouth or eating and try to be very careful about what you eat.

Questions for readers and listeners

Have you ever had viral gastroenteritis?

Do you know if you’ve ever specifically suffered from Norovirus infection?

Have you taken a voyage on a cruise ship?

Did you get ill?

Did other people get ill?

Did it smell of antiseptic to cover the smell of vomit and faeces?

Please leave your answers in the comments section of the show notes or on the Facebook page or on YouTube.

That’s episode 89 in the can.

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Medical Fun Facts is available in Anchor, the Apple Podcasts app, and in Stitcher. You’ll find the links in the show notes.

If you have any questions or comments please let me know. If I’ve said anything incorrect I welcome correction.

I’ll catch you next week for episode 90. Something beginning with the letter O. Send me suggestions.

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Thank you, and good night.

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