How does Norovirus Spread?

How does the virus spread, and for how long do people stay infected with it for?
24 February 2014

Interview with 

Lydia Drumright, Imperial College London


Lydia Drumright from Imperial College London is undertaking a new study to find out Kings Cross Station crowd controlhow the virus infects people and how long they remain infectious for. Kat Arney spoke to her.....

Lydia -   Hi, Kat.

Kat -   So, tell us a little bit about what do we know so far about kind of the life history of norovirus.  How it infects us and where it goes in populations?

Lydia -   We actually don't know a lot about that.  There's a number of studies that have been conducted, looking primarily at the strains that Ian talked about, the predominant strains in Sydney that people may have heard of recently which was last year's strain was reported on quite widely.  But one of the important factors is that we only look where people are symptomatic.  So, where people are part of an outbreak, those are who are collected into studies.  What our study will look at is not only those people, but all the people around them because we're concerned that people are becoming infected and shedding without actually being symptomatic.

Kat -   So, the main way that you get rid of virus from your system is by vomiting and diarrhoea.  How could people just shed the virus when they're not having severe symptoms?

Lydia -   So, the thing about infectious diseases that we're learning is that actually, we have what we call carriage and we have what we call infection or symptoms.  And so, you don't actually get rid of the virus by vomiting or having the diarrhoea as Ian had mentioned.  You get rid of it by an immune response.  And so, the process of shedding the virus happens whilst it's in your body and different people have different immune responses.

Kat -   So effectively, you can be not vomiting, not having diarrhoea everywhere, but you can still be dispensing virus to your family, your friends, your colleagues?

Lydia -   Exactly, secretly dispensing virus if you will.

Kat -   So, what are you trying to do with this study?  As you're studying it in people in populations, you're also trying to find out where does it hang out? As Ian said, it can hang around in the environment for up to 10 days.

Lydia -   Exactly.  So, we're using hospitals as sort of our microcosmic environment if you will and we are swabbing the ward areas. So, people have done this after there's an outbreak and they see lots and lots of norovirus.  We want to swab all year round, so we're doing weekly swabbing to see when it's there, if it's there, where it's hiding out, and also, looking at the symptomatic and asymptomatic people.

Kat -   And do you have any idea of the kind of patterns that you're looking for?

Lydia -   So, what we're looking for and we might be hoping to see is that actually, environmental swabbing will tell us when we should be expecting outbreaks in the hospital.  So in other words, we might not see any norovirus, or we might see it at a very low level, and then as that level increases, we wonder if that will lead to outbreaks or not.

Kat -   The results from that could be really powerful for hospitals trying to cut down on infections.  It surprises me that this kind of thing isn't done already?

Lydia -   I would agree with that.  I think that there's been a lot of challenges to funding environmental studies and this was the one question I think reviewers had on our study as well.  They said, "Well, I'm not sure how strong of a component the environment is, but we like the rest of the study, so go ahead and fund it."  But actually, I think the environment is very important.  We talk about it a lot for MRSA and other infections that we know about and we just don't know how it's playing a role.

Kat -   And it seems quite sobering as well that as Chris said, the advice is, once you've had norovirus, after about 48 hours, you're feeling okay again.  It's quite sobering to think that people could be infectious for much longer than that.  Do you think that that should change advice on what people should do?

Lydia -   At the moment, I would say no.  So, we do know from previous studies where they infect people, deliberately, healthy volunteers, with norovirus that the average healthy individual sheds for up to 3 weeks.  What we don't know is, how infectious that shedding is and how that contributes to the environment or further outbreaks.  So, at the moment, we should probably stick to the guidelines because we don't want healthcare workers certainly off for 3 weeks.  That would cause a huge problem for the NHS.

Kat -   Well, especially if people are feeling fine again after 2 days, I guess.  But thanks very much.  That's Lydia Drumwright from Imperial College London.


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