As we begin to reopen, what are the high risk activities?

Yesterday, my friend Lucinda posted a well written article by Dr. Erin Bromage: The Risks - Know Them - Avoid Them.  I have some issues with some of his statements, but I strongly agree with his main thesis:  There's a certain number of viral particles someone needs to take in for them to be infected with COVID and you can either get them from one big burst (like someone coughing in your face) or in smaller doses over time (like having a 50 minute conversation with someone who never coughs or sneezes).  The result is that some activities, like shopping, may be less hazardous than you imagine and others, like eating in a half empty restaurant, may be much more hazardous.

Rather than just rehashing Erin's well-crafted explanation of this concept,  I encourage you to spend a few minutes reading it before I get into the implications of viral loads.


 All finished?  Great!  Let's dig in...

Implications Of Asymptomatic Carriers. 
By now,  everyone has probably heard of the large number of people who have tested positive for COVID but never experienced any symptoms -- if they hadn't been tested, they'd have no idea they had it.  There's a big question about whether these people can pass on the virus.  If they can, then it means that the strategy of self-quarantining people with COVID symptoms won't much slow the pandemic because of the many people who would have no known reasons to self quarantine that could continue to infect others.  For a long time, I didn't think this was a big factor because the original case tracking in Wuhan found very few, if any, cases that couldn't be connected with a know person with symptoms -- there were few if any cases where someone got the virus and nobody could identify someone with symptoms who could have given it to them.  The second reason is that if you're not coughing and sneezing,  how much viral material can you really be passing on to others.

How many people have been infected with COVID by asymptomatic transmission is still up to question, but the research cited in Erin's article shows that virus droplets can be passed just through breathing, talking, and other basic behaviors ( the research was on other diseases like the flu and tuberculosis, but it's reasonable to expect its also true of  COVID.  The transmission is at much lower amounts, though, so you're unlikely to get COVID just by making short contact with an asymptomatic, but if you spend a few hours (or share a home) with them,  your chances could be good.

Quantity May Affect Severity
It's been found in other viruses like the flu that the amount of the virus you initially take in effects the severity of your illness.  It hasn't been confirmed if this is the case with COVID, but the number of very light and asymptomatic cases makes it a plausible hypothesis.  Someone with a more severe COVID case would have a bad cough and other symptoms that could transmit a lot of virus in a brief time, but they would also (hopefully) self-quarantine soon after they started experiencing the symptoms so there wouldn't be many opportunities to infect others.  On the other hand, someone with little or no symptoms with potentially be in contact with more people over more time, but would be distributing much lower volumes of virus particles. From the articles example,  a single cough could potentially deliver many times the minimum dose to infect someone but it might take a 50 minute conversation with someone with a light case to get infected.  My suspicion is that those who have light or asymptomatic cases most often got the minimal dose for an infection from other asymptomatics, who barely gave them enough of the virus to be infected.

To be clear, there hasn't been enough studies to prove this suspicion, and I'm stacking one unknown (does amount of virus effect whether someone is asymptomatic) on another unknown (do asymptomatics infect others).   I should also point out that research has found that people tend to have the highest quantity of viral particles right around the time they start experiencing symptoms so most people with COVID could be infecting others with lower doses before they start coughing and sneezing.

If we believe that masks are effective at trapping most of the viral particles an infected person has (I haven't seen a study confirming it, but it makes intuitive sense), then wearing masks while around others would be a game changer in terms of reducing the amount of particles others are absorbing while around you.  While non N-95 masks may not filter something as small as a COVID particle, even if it trapped half the particles it would mean it would take 100 minutes of conversation with someone infected to become infected instead of 50 minutes.

I should also note that just because someone isn't coughing or sneezing doesn't mean they can't deliver a high-volume of virus particles to someone else.  If you are in the same home with someone else, you have hours and hours to infect them -- potentially at high levels.  That's what happened with measles.  Typically, one child would have a casual contact with someone infected and bring a light case of measles home with them. Then their family would experience more severe cases from longer exposure to that child.

If it turns out that people with light or no-symptom cases of COVID tend to infect others with similarly mild cases, it could be very good news because it may mean that COVID is self-inoculating -- along with the visible severe cases, it even more quickly spreads light cases that can lead to group immunity. For this scenario to happen, people with light cases would have to develop COVID immunity -- something that also hasn't been determined yet.

Besides severity and asymtomatic carriers, there are many more implications of Erin's essay I'd like to explore:

Air Conditioning:  It seems likely (and early research supports) that once outside the body, COVID does much better in dry cool air (and electric light)  than it does in warm humid air and sunlight.  I've pointed out that tropical countries have had much milder COVID experiences than northern ones (see Graph), but Singapore has recently had some concerning COVID growth.  Singapore's founder practically build the country on Air Conditioning while the other countries in Southeast Asia still operate largely without it (though they're increasing adoption).  I ran a comparison of AC use and COVID Cases and saw what at least looks like a correlation:

Note that the US has lower AC use per capita than Singapore because of the winter season, but during that time, we are also in cooler, dryer spaces.  If AC is a factor in COVID spread,  then some of the less effected states, like NC, may see a spike in July/August where people tend to retreat indoors to air conditioned spaces.

Affect on different businesses:
If the guesses above are right,  it leads to a few principles on what's (relatively) low risk and what's high risk:

LOWER RISK

• Staying Home (if you know those at home are not infected)
• Short Interactions with strangers
• Interactions outdoors with fresh air (and better yet Sun)
• Locations where most or all are wearing masks

HIGHER RISK

• Extended Time Indoors with the same strangers
• Venues where many people are talking
• Air Conditioned spaces with many others and recirculated air
• Places where groups are largely not masked
• Working in a place that has a lot of interactions with potentially infected people

So what does that suggest about the prospects of different places reopening? 

• Most shopping venues are relatively safe (for the shoppers), especially if masks are required in the shop. The shop clerks are at higher risk because of the number of potentially infected people they encounter.  The plexiglass screens should significantly reduce their exposure, though, because most of the particles will fall downwards when a person breathes. 
• Restaurants will be hard.  You can't wear masks while eating, so you would potentially have a lot of unfiltered particles.  Servers can't stand behind plexiglass and may have trouble wearing a mask since many people will have a hard time understanding them.  Outdoor seating, even on hot days, should be safer.  Shorter dining times should help for the patrons.  
• Bars, particularly indoor ones, involve a lot of people close together, unmasked, and potentially with impaired judgement. People can spend much longer at a bar than at a restaurant as well, increasing their exposure to anyone infected in the space.  Bartenders will have an even harder time.
• Hair and beauty places seem relatively safe (for the patrons) for procedures that are an hour or less.  Those working there are at higher risk.  
• Movie Theaters -- Air conditioned spaces with a number of strangers. If people can get comfortable wearing a mask for 2 hours, it be reasonably safe. Comedies and horror movies that provoke a lot of laughter and screams from the audience would make their situations riskier.  There will have to be a way to clean all the surfaces in a theater between shows, which will reduce the number of shows a movie can provide.  Also for seating,  groups who are already exposed to each other will be clustered, but away from other groups.  This could require a smart seating reservation system that automatically blocks out seats to space groups who book together. 
• Churches -- the higher risk time would be when everyone is singing together.  Singing normally involves taking deeper breaths and expelling more air than talking.  It would also be harder to do through masks.  Churches opening in the next couple weeks should consider playing recorded music and asking the participants to join silently in their hearts.   Communion and offerings could also be tricky because it normally involves people handing a basket or elements from one end of the row to the other, which doesn't leave room for cleaning surfaces. 
• Sporting Events -- outdoor events where there is air circulation and (sometimes) warm air and sunlight are less risky than indoor ones.  Masks should be worn, and teams should be working to provide something fun with team colors that can be given away at the door (and paid for through higher ticket prices). Several companies have already produced Banditos (or tube scarves) and you can expect Nike, Adidas, Under-Armor, and others to jump on this train quickly.  The high risk time here seems to be in an enclosed air-conditioned space roaring with fans.  Extended fan noise is like singing -- everyone expelling more from their lungs and taking deep breaths.  
• Office spaces --  workspaces will move more towards social distancing --less community tables and more cubicles and offices.  The increased space per worker may be offset by having workers rotate between the office and home.  Traditional air conditioned spaces with no open windows will seem less safe.  Closed meeting rooms is where the real focus will come because you will have people grouped together and all talking.  Buildings may need to focus on the air handling of these conference rooms to constantly move fresh air into the space while keeping the temperature comfortable.  
• Schools -- There was a promising report recently that looked at COVID contact tracing from several studies and found there wasn't a single case of a child under ten passing on the illness to an adult.  The study also reinforced that children tend to get much milder cases when they do contract COVID.  If the research holds up, it could make schools safer for students and teachers than was feared. On the other hand, some school districts are already proposing removing PE, Choir, Band, and other large group programs from schools.  

Clearly from these examples,  reopening plans will be complicated and almost every industry will have different challenges.  Eventually, vaccines, group immunity, and therapies to reduce the severity of COVID will reduce the risks and make all activities safer, but you can expect it to be slow moving and with many mistakes.  Best to be patient, considerate, and thoughtful about what risk you take in the meantime.