There are four simple concepts which will help you stay safe and avoid contracting Covid-19 as you begin to reenter society, and as things begin to open up.
- Proximity or closeness to other people outside your own household. A very safe distance is 10 feet, and adequately distance is 6 feet, and anything less than 3 feet of social distance is probably risky.
- How long you are in contact with those people. Studies of transmission suggest that a contact time of 30 minutes or more is risky, but in situations of close social distance anything more than five minutes may be risky. (If everyone is wearing a mask, safe contact times may be somewhat longer.)
- Whether the environment is confined or open, inside or outside, and if inside how large is the inside environment and is there good air circulation? Outside is almost always better than inside, and inside environments which are larger and have good air circulation are probably less risky than small and sealed environments like elevators. (Or small public restrooms.)
- Whether or not everyone is wearing a mask. Studies suggest that the use of masks can reduce transmission by 80 or 90%. That is why doctors and nurses always wear masks when treating sick Covid 19 patients. They also wear eye protection. The use of masks protects you from spreading coronavirus to other people, and also protects you from them spreading coronavirus.
When the more dangerous options among these four factors overlap, you are in peril.
For example, let’s say you decide to get a massage. The massage room is inside, very small, and the massage takes 90 minutes. This is a high-risk situation even if you and the masseuse are both wearing a mask. (And even higher risk if either is not wearing a mask.) You have close social distance, extended exposure, in a small and poorly circulated room, and perhaps the only safety factor is the wearing of masks.
In contrast, you go for a walk in your neighborhood. Other people are out walking but everyone respects at least a 6 foot social distance, and you do not stop to talk with people. Any contact is 6 feet away and lasts only a few seconds. This is a relatively safe situation regardless of the use of masks.
Let’s look at each factor separately.
Indoors versus outdoors
Japanese researchers looked at 110 people who had Covid-19. Only 12.5 percent passed the illness on if their only interactions with people were outdoors. But of those who interacted with people indoors, 75 percent infected other people. Out of the 22 people who met people indoors only six did not infect anyone else. But of the 88 people who met people only outdoors, 77 did not infect anyone. The reason for this appears to be that the tiny droplets that can infect you disperse very rapidly outside. So it appears that outdoor contact is not perfectly safe, but is six times safer than indoor contact.
Duration of contact
There is some interesting data from China and France in terms of likelihood of catching Covid-19 in various different indoor settings. The worst setting was the household where 13 percent of people contracted Covid-19 if someone in their household had it. The next most risky type of environment was public transport, which ranged from 2% to 12% depending on whether or not there was a super spreader event. (Super spreader events are those rare people that seem to be very efficient at spreading the virus.)
Particularly relevant was the finding that 7% of people who came into contact with an infected person in a restaurant dining environment contracted Covid-19. That’s pretty risky to avoid cooking at home! (Note that 85 coronavirus cases were linked on 6/28/20 to a SINGLE restaurant in Michigan, in a single week of operation! The restaurant had poor circulation, poor social distancing rules, and no air filters on ventilation.)
All the other indoor environments had about the same risk, 2%, and this included shared work or study spaces, schools, healthcare settings, and all other settings. The better the ventilation was the less likely transmission.
What about masks?
Masks are particularly helpful in high risk indoor situations, where they block the spread of droplets that can transmit Covid-19. Because the risk of infection is lower outdoors, especially if people are properly socially distancing, they may add very little benefit. But if you are in close contact with other people outdoors, masks may help significantly. This may be why in cities that had large Black Lives Matter demonstrations, there were relatively few outbreaks, as many of the protesters wore masks.
Large events are particularly problematic because of super spreader individuals. Research from China and Hong Kong showed that 80% of new infections came from about 20% of people. These are called super spreaders, and we don’t really fully understand why some people are so infectious. But being in a large event such as a sporting event or concert makes it highly likely that there will be one or many super spreader individuals. Avoid these even if they reopen. (As reported on 6/28/20, Swiss authorities had to quarantine 300 people who attended a Zurich nightclub on 6/21/20 because of a super spreader individual.)
High-risk versus low risk situations
Here’s the deal with viral particles. We still don’t really know how many Covid-19 infectious viral particles it takes to get you sick. But some experts estimate that the threshold may be about a thousand particles. A cough releases 3000 droplets and a sneeze releases about 30,000 droplets. These droplets can contain 200 million viral particles, which explains why symptomatic people can spread Covid-19 indoors so easily.
In contrast a single breath releases about 50 to 100 droplets, which fall to the ground quite quickly. Although we don’t know the exact data it’s reasonable to assume that a person breathing may release 30 viral particles per minute. Speaking may change that to 300 per minute. So, this tells you that it would take perhaps 40 minutes of someone breathing near you, or about five minutes of someone speaking with you face-to-face in order to risk infection, assuming it takes 1000 viral particles to contract coronavirus.
This is important because it tells you that if you walk by someone outside or even inside in a grocery store, your risk is low. But let’s say you see a friend of yours in the grocery store, and you spend 15 minutes talking with them. That’s pretty high risk especially if you are face-to-face and not wearing a mask.
Where have most infections occurred?
- Long-term care facilities
- Meatpacking plants
- Business networking and conferences such as the Biogen conference in Boston in late February
- With more relevance to most of us, weddings, funerals, birthday parties, family get-togethers, which make up about 10% of the early super spreading events
Most of us aren’t in prison, we don’t live in a nursing home, we don’t work in a meatpacking plant. But many people have lately been tempted to go to parties which are clearly a high risk situation.
Finally, don’t forget to wash your hands or use alcohol gel. Don’t touch your face which includes your eyes, ears, nose, or mouth. When you get home wash thoroughly, and you may want to even jump in the shower and wash your hair, as some studies in medical settings have found that hair is particularly good at holding viral particles.
Here’s a good way to think about risk. It comes from advice about sexual health. If you have sex with someone, you are being exposed not just to them but to all their prior sexual partners. In a similar way, let’s say you get together with her friend who is not part of your household. You’re not only being exposed to them, but to every person they have had contact with in the last 14 days or so. The clerk in the store who didn’t wear a mask and stepped close to them, the UPS guy who knocked on the door and asked a question from 2 feet away, all the friends that they have had contact with, the people they live with, and all the people that those people have had contact with. As you can see one of the reasons coronavirus spreads so much is that the larger our social networks are the more risk there is.
Finally, be aware that many coronavirus infections are asymptomatic meaning that the people who have coronavirus are neither coughing or sneezing. Some studies suggest that as many as half of the cases are asymptomatic. This means you can’t depend on people knowing that they might be sick. The Center for Disease Control released data on June 26, 2020 that suggests that the real number of coronavirus infections is perhaps 10 times what has been reported. As of today, there are about 2.5 million cases reported in the United States, which means we may have had 25 million cases! That is 7.5% of the US population. This sounds like a lot, but it also means that 92.5% of the United States population is still in danger of contracting the coronavirus.
And that is why I’ve been practicing virtually since early March, and will continue to do so until there is either an effective treatment or a vaccine for the coronavirus. Be safe out there, and ask yourself about each activity if it is worth the risk not only to yourself, but also to all the people you might come into contact with including older parents and grandparents. We are all in this together, and even the young and healthy can transmit coronavirus if they get sick. Yes, we all miss going to restaurants, movie theaters, bars, parties, concerts, and sporting events. But it’s not permanent. I suspect that within the next six months will have much more effective treatments, and within 12 months we will have a vaccine which will let us get back to normal.
Dr. Andrew Gottlieb is a clinical psychologist in Palo Alto, California. His practice serves the greater Silicon Valley area, including the towns of San Jose, Cupertino, Santa Clara, Sunnyvale, Mountain View, Los Altos, Menlo Park, San Carlos, Redwood City, Belmont, and San Mateo. Dr. Gottlieb specializes in treating anxiety, depression, relationship problems, OCD, and other difficulties using evidence-based Cognitive Behavioral Therapy (CBT). CBT is a modern no-drug therapy approach that is targeted, skill-based, and proven effective by many research studies. Visit his website at CambridgeTherapy.com or watch Dr. Gottlieb on YouTube. He can be reached by phone at (650) 324-2666 and email at: Dr. Gottlieb Email.