So, why exactly are airports such effective facilitators for the spread of disease-causing pathogens? Well, between the mixing of individuals from around the world, the close proximity of areas like security and a lack of focus on personal hygiene, there are plenty of factors to choose from. And of course, all of those factors are exponentially more significant for the world’s busiest aviation hubs.

“These are airports that are super-spreaders themselves,” says Nicolaides. “They have a lot of outgoing traffic, and they are well-connected with other international destinations that span the whole geography, for example [New York] JFK or London Heathrow.”

While hand-washing rates at airports will have climbed significantly in the era of Covid – where airports are still open, at least – in normal conditions, hand hygiene practices leave something to be desired for most passengers.

“I went through some statistics,” says Nicolaides. “If you do some back-of-envelope calculations, you will find that if you go to any airport around the world at any given moment, and you measure how many people have clean hands, you will find that only one in five have clean hands.”

With an average hand-washing rate of around 20% in most scenarios, what would be the effect of increasing this rate on limiting the spread of infectious diseases? This is exactly what Nicolaides and his colleagues set out to model in their study, and the findings are striking.

“If you go to all airports in the world and increase the level of hand-cleanliness from 20% to 30%, this will slow down potential disease spread by about 24% [in the early stages of an outbreak],” says Nicolaides. This means a 24% reduction of new cases worldwide, which would have an immense impact on the early spread of a highly contagious disease.

Changing public behaviour is challenging under any circumstances, but Nicolaides acknowledges that bumping the hand-washing rate from 20% to 30% at all 3,500 airports worldwide would be “quite impossible”. So the team also modelled the potential impact of making the same increase across ten of the world’s key air hubs – the super-spreaders of the aviation world. These comprise London Heathrow, LAX, JFK, Paris Charles De Gaulle, Dubai, Frankfurt, Hong Kong, Beijing, San Francisco and Amsterdam Schiphol.

Even making hand hygiene improvements at these ten airports would have a significant impact according to Nicolaides and his team, with potential disease spread reduced by 8%, and as much as 37%, while the range for all airports worldwide spans from 24% to 69%. In the event of an outbreak like the one we are experiencing now, those percentages could equate to thousands of lives saved.

Of course, improving the rate of hand-washing at airports even by a modest 10% is no mean feat, especially after the residual shock of the Covid-19 outbreak has worn off.

At all airports in the world, the only place that offers some personal hygiene [to passengers] is inside the restrooms,” Nicolaides says. “That’s not enough to facilitate personal hygiene for individual travellers. You [also] have to make people understand that washing your hands with water and soap for at least 15-20 seconds is important for our health and the health of others around us. These are the two barriers – one is capacity, and the other is educating individuals.”

Although the Risk Analysis study was a statistical effort rather than a social study, Nicolaides cites studies noting that prominent signage in corridors and outside toilets reminding people to wash their hands can be helpful in medical settings, although these measures may be less effective in the airport environment.

Amid the Covid-19 crisis, some have called for hand hygiene to become a core part of airport security, with hand sanitising stations installed for passengers to use as they move through checkpoints. Conor Friedersdorf, writing in The Atlantic, argued that at US airports, security staff should “let travellers leave their shoes on if they wash their hands for the 15 to 20 seconds that doctors recommend”, adding that “we go to far more trouble at airports for measures that are more intrusive and burdensome and that save far fewer lives”.

Nicolaides, however, sees effective communication and building capacity in hand-washing stations as a better solution, in the long term, than heavy-handed requirements at airport security, which would bring “longer lines and frustration” for passengers.

“I would like to see, for example, hand-washing happening outside the restroom as well, so you have hand-washing stations around the airport,” he says. “Also I would like to see some communication messages making people aware that this is right for themselves and right for their surroundings. I don’t believe in making requirements for people – maybe now it’s a measure that many governments are taking, but in the future, I don’t believe that this is the right way to do it. The best way is to make people want to clean their hands, and at the same time [building] the capacity to facilitate that.”

Whatever the means employed to achieve it, the study by Nicolaides and his colleagues provides statistical evidence showing the value of better hand-hygiene engagement at airports when it comes to major outbreaks like Covid-19. Governments are now trying to slow the spread of the virus through social distancing, and a cleaner airport environment could buy precious days to help slow down future contagions.

“Enhanced hand-washing and other sanitisation methods inside airports and aeroplanes will make things a little bit better, and may allow airports to operate for a little longer,” Nicolaides says. “I’m not saying these kinds of measures are in any way going to kill off the disease. These kinds of measures, and all of the measures that we see all over the world, are methods to slow the spread of the disease. Even if you close 90% of the airports and flight routes, things are still going to spread. Maybe they will spread slower, but they are definitely going to spread. This kind of measure could save some extra days for the air transportation network.”