A good dose of fresh air and sunshine is what we all need right now. Relaxed pandemic measures, reopening of parks, and pleasant weather makes it tempting – not to mention essential for our sanity – to enjoy the outdoors with friends and family. But meeting outside doesn’t mean that we should be cavalier about the spread of SARS-CoV-2, especially because there are still no vaccines or treatments available.
COIVD-19 transmission indoors vs. outdoors
Effective COVID-19 spreading occurs in one of two ways. The first is through direct transmission, which is when an infected person talks, sneezes and coughs and their respiratory droplets fly through the air, and a person in close contact inhales them. The second is when infected droplets end up on a surface that is touched by someone else who then touches their nose, eyes or mouth. Fortunately, these transmission routes are less problematic when you’re outdoors because there are wide-open spaces for you to keep the needed distance and fewer communal surfaces to touch. But we still don’t know the risks of outdoor COVID-19 spread.
And while most of us have read the basics, sometimes it’s good to review: The SARS-CoV-2 virus is about 0.1 microns in diameter, which means that an infected person through breathing, talking and coughing will produce 1-10 micron aerosol droplets that may contain many thousand live viruses. Even though aerosol is not the primary transmission mode of SARS-CoV-2, it is still a possible route of infection.
When indoors, an infected person who releases virus in their droplets may increase the risk of direct transmission to others based on the size of the room, ventilation and air circulation. The higher the density of infected droplets in the air, the more likely the spread to one and probably more people.
Outdoors, it’s generally safer. Typically, infectious materials carried in the air, or airborne contagions, seem less worrisome. But there are several unanswered questions about this coronavirus and the risk of outdoor transmission, because this virus is new and the science is still being developed.
For instance, we don’t know whether the virus remains viable in the air or how long it is infectious. We also don’t know how many are needed to infect another person. There are early reports that live virus is in the air in crowded public places. But when people are at least 1.5-2 meters away from each other, there is less of a chance for transmission because the virus needs to enter your upper throat or respiratory tract or land on your hands, which you then would use to touch your face. And being outside allows for easier social distancing without being anti-social.
There are other questions: If the virus is viable outdoors, then what are the effects of sunshine, for example, or wind, rain, temperature, and humidity on its degradation, infectivity, and spread? Other viruses degrade with high heat and moisture, and direct sunlight. But there is still limited information about SARS-CoV-2. So far, testing has revealed little impact of high temperatures and high humidity, and no clear answer about whether it will go away during a hot summer.
There is hope, however, when it comes to sunshine and the virus. UV light appears to decrease SARS-CoV-2 viability on surfaces. Most of us know about UVA and UVB in sunlight, but we know less about UVC, which is the best UV light for destroying viruses. High dose UVC is a sterilization method in hospitals and can kill most viruses, including SARS-CoV-2. But while there may be some destruction of this coronavirus on surfaces left out in the sun, it isn’t a reliable method for disinfection, because we don’t know what strength of UVC is necessary and how long it takes for it to work.
Planning outdoor gatherings
So the good news is, we can now meet up with family and friends. But there are still a few things that you should do to reduce the risk of COVID-19 infection.
First of all no hugs and no handshakes – these gestures we love will have to wait. In fact it’s best not to get any closer than 1.5 meters, and to limit the group to a maximum of 10 people. It’s also probably best for everyone to bring a mask to wear to protect others – use you good judgment on when – and have a stash of disinfectant and hand sanitizer.
Second, pick the place and time carefully. Ideally, it’s best to find an area without large crowds, or at least a time when fewer people are around, like between meals for a snack or a drink. Try to cordon off the area with extra picnic blankets or empty carry crates, to set up a space that allows for social distancing between groups of friends and family who are not quarantined together. Best also to choose a place that’s not too far from home to avoid having to use public toilets.
If it’s a picnic, all the guests should bring their own picnic blankets or garden chairs, their own food and drink, utensils, glasses, plates, and cutlery. The less passed around the better.
So at least for now, playing it safe means continuing to maintain that social distancing we all wish we could do without; it means washing your hands or using hand sanitizer. And it still means wearing masks, even when socializing outdoors.
Some day when this is all over, these will be the stories we will tell our grandchildren, who will think we’re making them up. But at least we’ll be there to laugh about it.