Are aeroplanes spreading diseases?

By air, you can travel around the globe in much less than 80 days, which means any infectious nasties you caught on holiday could spread easily and rapidly around the world. What is the risk? Infectious disease expert Steven Riley, from Imperial College London, spoke to Kat Arney about whether planes really are spreading disease...

Steven - I think from some of the recent high profile outbreaks - if we go back to SARS or the 2009 pandemic and even the recent Ebola epidemic - I think we can be pretty confident that those long range, the initial long range, infection events are coming on aeroplanes.

Kat - How do we know that they actually are? How do you pin them down instead of just going, "They must be. It's popped up here, it's popped up there. It must have come on a plane?"

Steven - So, there's a few different ways that it's been looked at. Particularly, with some of these infections that when almost everybody that gets infected turns out to have symptoms. We have a lot of case-based data. We can trace the original roots of the SARS epidemics through particular hotels in Hong Kong and then flights that went out to Canada. So, even that traditional epidemiology can trace a lot of these events back. And then beyond that, when the number start to get a little bit bigger, we can do some fairly straightforward calculations and from the airline data, we know where people travel. So, we can make predictions about where the cases are likely to pop up and when they're likely to pop up. And generally, they work pretty well.

Kat - Are there any diseases that are more or less likely to spread? I mean, we heard so much about the Ebola outbreak. But you've mentioned SARS as being more of a problem. Are there particular diseases that really like to get on a plane and go?

Steven -   There's quite a bit of evidence out there about influenza and that it does spread around the world on planes, that it does also manage to infect people whilst they're actually on the plane. There is some good work on some of the bacterial pathogens as well. But it's difficult to know because it's so subject to what scientists choose to study.

Kat - And the key thing is really - I go on planes occasionally, lots and lots of our listeners I'm sure do travel by air - how much of a risk is it that diseases or even major outbreaks will be spread? What can we do to prevent/protect ourselves?

Steven - There's a lot of good evidence from those early stages. So, that is when diseases will spread, but that's not going to affect most of us the vast majority of the time. Public health authorities recommend the standard procedures for protecting yourself from respiratory infections. So, regular effective hand washing and things like that. So, the really difficult question is, how much more risky is it to be on a plane on any given day than to do some other activity in your life? And that is a very difficult question to answer.

Kat - So, is it more dangerous to be on a plane than say, on the London underground tube? I mean, London is a huge melting pot for the world.

Steven - That's right and these are the types of questions that we are trying to get into now. It boils down to some really interesting stuff about routes of transmission. It's very disease specific but again, for influenza, how much of it is really aerosol? If someone sneezes in a tube train, do you really have a risk of getting 'flu from that person or is it that they don't use a handkerchief properly and it goes via the door to your office. Those are the questions. There's a lot of work going in to trying to answer that so that we can think about quantifying those specific risks.

Kat - We've only had these kind of means of travel for a few hundred years and before that there were ships and people traveling around the world. But really, in terms of human history, we've not been super mobile and suddenly, we're spreading these viruses and pathogens all over the place. Should we be concerned about this?

Steven - I think there's lots of evidence all the way back through human history that as we live in more dense populations and as we become more connected that we do enable the spread of disease. There's great evidence from archaeological findings and careful analysis how smallpox originated in kind of northern Africa and then into Europe and didn't actually reach the Americas until the Europeans started going over there regularly. So, these things have been happening throughout history and we don't know that maybe we've been through all the bad ones or most of the bad ones. So, it's not clear that it's definitely a negative, but there's lots of examples of how the increasing density with which we live, which are designed with a better connectivity, does allow new things then.

Kat - One of the things that my friends and I sometimes joke about is, if we go on a plane, we always feel a bit grotty afterwards. We call it plane 'flu. Is there actually anything intrinsically unhealthy about being locked up in an airplane cabin? Is this true that people do tend to get sick after flying?

Steven - I'm not sure how good the evidence is that you get a much higher risk. I think if someone around you has just become infectious with the respiratory pathogen and they're coughing a lot then there's good evidence that you don't want to be in the two seats very close to them - sharing a row or sharing two rows is not so great either. Further away than that is a little bit better. So, there's some noise about that, but I mean, it's not entirely my area, but I'm sure just being in a lower pressure and getting a bit dehydrated and feeling a bit dried out probably makes us all feel a bit grotty after a very long flight.