The new Wuhan Coronavirus outbreak (which has officially been named Covid-19) has renewed interest in pandemics, the risk of having one, and how to prevent them. As is often the case, people tend to focus their attention suboptimally, based largely on fear or availability, not on hard numbers. There is talk of closing borders, and no story about the Coronavirus is complete without a picture of many people wearing surgical masks. What we should be showing is a picture of someone washing their hands.
A new study looks at the epidemiology of pandemics – worldwide spread of a contagious disease – and the impact of improving handwashing at airports, especially key travel hubs. The results reinforce the importance of hand-hygiene in preventing disease spread.
Only about 70% of people, for example, wash their hands after using a public restroom. Of those, only about half wash with soap and water for the requisite 15 seconds minimum. The study authors estimate that at any given time only about 20% of people moving through an airport have clean hands. The rest are at risk for carrying pathogens, as they operate kiosks, use handrails, touch the arms of chairs, and elsewhere. The risk for spread of disease is therefore immense.
They further identified the 120 airports around the world that are most influential in spreading disease. These include the most trafficked, but that was not the only criterion. Having a position between different regions, and therefore serving as a gateway, is also important. Connecting to large international hubs is also a factor. They conducted simulations of disease spread involving these airports. To drill down a bit further, they identified the 10 most important airports to a hypothetical outbreak location. They then examined the impact of even modest increases in handwashing at those 10 airports.
First, by increasing “traveler engagement” with hand hygiene at all airports, the risk of an outbreak turning into a pandemic can be reduced by 24-69%. By focusing just on the 10 most important airports for a particular outbreak, the risk of spreading to a pandemic can be reduced by up to 37% – that’s with just increasing hand-hygiene messaging for passengers at 10 airports.
The results suggest that handwashing is likely the single most effective method for reducing the spread of flu-like viral illness. This should not only focus on airports, although they are the most important for global spread. Any public location is a potential risk for the spread of viruses, and being careful what you touch, plus practicing good hand-hygiene while in public, is an important safety measure.
What about those masks? The bottom line (for basic surgical masks) is that they block large particles and droplets, but not small particles. This does reduce the spread of respiratory pathogens from a sick wearer. So if you are sick and you are going into public (which you probably should not do), wearing the mask will partially protect others. If you are not sick and want to protect yourself from getting a pathogen, the mask modestly reduces your risk – if they are worn properly and consistently. But this benefit is only measurable if you are in the middle of a disease outbreak.
So, for example, if you are in China there may be some benefit to wearing a mask (tightly and consistently) if you are going out into public. Outside of China, in the US, for example, there is no reason to wear a mask and it will likely be of no benefit. In other words, there is no evidence for routine preventive use, only for use during an outbreak.
What about travel restrictions? These make intuitive sense – a contagion is spread internationally largely through air-travel, so restrictions should help. However, the evidence does no support travel restrictions as a policy solution. A 2014 systematic review of travel restriction for influenza outbreak found that it only delayed, but did not prevent, international spread. A 2020 review for non-influenza viruses, which would include Coronaviruses like SARS, MERS, and the current Wuhan strain, found minimal evidence for effectiveness. This is not the same as concluding it doesn’t work, and the authors called for more research.
The evidence is mixed, however. A 2006 study found a substantial role for airline travel in the spread of influenza virus. Another study from 2006 found benefit to reduce the spread of a moderately contagious disease by restricting regional travel >50 km. I think the bottom line is that travel restrictions are not as effective as we thought, but we need more research to understand its impact better.
Meanwhile, there is also evidence for major downsides to travel restrictions. They reduce information sharing, and the availability of resources in hard-hit areas. This may paradoxically increase a local outbreak, feeding into an epidemic and even pandemic, while only delaying the inevitable.
Combined with this evidence, the current study suggests that our efforts might be best focused on increasing hand hygiene at airports, especially those that are vital hubs to the outbreak region, rather than restricting travel. Masks in targeted areas, with proper instruction on use, may also have a benefit, but probably not as much as handwashing.
The latest numbers (which will be out of date by the time you read this) as of 2/11/2020 is that >40,000 cases have been confirmed in China, with >1,000 deaths. The numbers are still increasing geometrically, and we don’t appear to be close to the end of this epidemic, which has a high risk of turning into an official pandemic. These numbers are still dwarfed by an average flu season, to put things into perspective. There have been 13 million flu cases so far this season, with >6,000 deaths. The death rate from the novel Covid-19 Coronavirus is greater, but so far the total cases are lower by orders of magnitude. Only time will tell how big this epidemic will get.
