PSI Blog 20200601 Coronavirus Hates the Outdoors
Pardon
the teleology, but I just had to do a little off-topic speculation on our
current predicament. It is becoming clearer every day that air-borne viruses do
not do well in the outdoors. Mom’s advice to “get some fresh air” seems
well-taken. The energy saver’s advice to tighten up every window and door seal
might just give those little buggers plenty of time for you to breathe them in.
The advice to put on that mask when you leave the building might be
backwards—maybe you should put it on when you go inside. Instead of “sheltering
in place,” maybe we should “shelter out place.”
There
now are plenty of data showing that being inside with carriers during a
pandemic is not a good idea. The coronavirus is spread many ways, but it looks
more and more like the finest aerosols (less than 5 um) are the top culprits in
most cases. The mainstream press is finally waking up to the aerosol problem.[1]
A choir practice in Washington State was the site of a huge outbreak and offers one of the strongest pieces of evidence for airborne transmission. Satoshi-K/E+ via Getty Images
1. The first indication ignored
for far too long was the 2.5-hr Skagit County, WA choir practice in which 53 of
61 singers became infected with COVID-19 by a single carrier.[2]
The time from exposure to onset was 3 days, 12 days for hospitalization, and 14
days to death for the two that died.
2. A single carrier in Guangzhou, China
dining at a restaurant infected four at her own table along with five others at
adjoining tables.[3]
3. A single carrier in South
Korea partied at three nightclubs, infecting 54 people.[4]
4. In another incident, a “super
spreader” in South Korea infected 37 people in a church.[5]
5. After an employee got the
virus, a huge grocery in China had 8,244 shopper visits and only 2 (0.02%)
infections, while the 120 employees had 11 infections (9%), showing that
duration and closeness of contact was important.[6]
6. Two buses in China “brought
people to the same temple, where they mixed and mingled. But who was most at
risk of getting sick? Those who rode the bus with an infected person.
Twenty-four out of 67 people on that bus got sick. No one on the other bus did.”[7]
Lesson: Close quarters and duration.
Meanwhile, “in a study of 1,245 cases that occurred
across China from January 4 to February 11, only two cases were traced to
contact with an infected person out of doors.”[8]
To get infected, you only have to be exposed to
someone’s breath for less than the 15 minutes. The breath aerosol can stay in the
air for hours. Where ventilation is poor, as in a bar or bus, that aerosol
remains in the air and is replenished continually by the infected person. Six
feet of separation is not enough, particularly when the air is continually
stirred up by the motion of others in a small enclosed space. “Super-spreaders”
typically do not cough or sneeze on every one, they simply breathe, filling the
trapped air with tiny particles that take a long time to settle even when not
stirred. A runner or biker going fast past you is extremely unlikely to do
that.
Conclusion: Ventilation
Indoor air bad; outdoor air good. That is why we have many
more colds and flu in winter than in summer—it is not simply due to the
temperature—it is what the temperature makes us do to ourselves—breathe bad
indoor air. Being with a large group outside on a windy day would be much less
risky than being with the same group on a calm day. Athletics played outdoors would be much less
risky than those played indoors, etc. Voting in a well-used booth verges on
suicide, while voting at a table outside might be as safe as mailing a ballot;
teaching classes outside would be safer than teaching inside;
political demonstrations outside would be safer than those inside.
Again, the key to all this
simply is ventilation, and plenty of it. Note that in the restaurant case,
there was an exhaust fan on the left side of the room and an air conditioner on
the right (Figure). It was 79oF outside [9] and the investigators assumed the air conditioner was on even though swabs of
the conditioner and the exhaust fan indicated no virus. The infection pattern
does not support air flow from right to left. My conclusion: The air conditioner
either was turned off or was insufficient. Looks like we need more powerful ventilators before we get sick so we won't need them later.
In sum: We should avoid breathing used air.
Figure. Sketch showing arrangement of restaurant
tables and air conditioning airflow at site of outbreak of 2019 novel
coronavirus disease, Guangzhou, China, 2020. Red circles indicate seating of
future case-patients; yellow-filled red circle indicates index case-patient. Modified
from: Lu and others (2020) https://wwwnc.cdc.gov/eid/article/26/7/20-0764_article#tnF1.
UPDATE:
CDC Relents: Its Bad Air
After nearly a year of what was obvious when I wrote this Blog post, the CDC finally admitted that the Covid-19 virus spreads almost entirely via aerosol transmission: https://go.glennborchardt.com/CDC-admits-aerosols
In other words, and I repeat, it is bad air, not coughing, not hand shakes, not messy door knobs, but simply the air you breath that can get you infected. Six feet is is not enough in a crowded, unventilated room. A mask provides some protection for the wearer, but even that is insufficient:
Even N95s admit more than 5% and surgical masks admit 20 to 85%. Best to stay outside, and, then, only when the air is moving and no one with bad air is nearby.
[2] Hamner, Lea, and others, 2020, High SARS-CoV-2 Attack Rate
Following Exposure at a Choir Practice — Skagit County, Washington, March 2020:
Morbidity and Mortality Weekly Report, v. 69, no. 19, p. 606-610 [Here is the
summary: https://go.glennborchardt.com/Skagit-summary]
