Aerosol transmission indoors - Printable Version
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Aerosol transmission indoors - M T - 04-25-2020
I recently wrote:
Quote:The report on the restaurant infections showed people being infected apparently by the breeze from an air conditioner and its return flow, across a 6 meter room. The conclusion was that the particles had traveled up to 9 meters (about 30') in the breeze of the AC, and been concentrated enough to infect a person. That led me to wonder just how long it took for that air to flow that far, and how long do the droplets in a cough float.
A new study has gone to that restaurant and conducted experiments to measure airflow in the (larger) room (in the presence of warmed mannequins) on a similar day (external warmth & sunshine) and use tracer gas to measure a simulated flow of exhalation of the index patient in the room. With those results, they simulated the fluid dynamics of the air flows.
The study concluded that aerosolized virus (fine particles) from the exhaled breath of the index patient can explain the spread throughout that area (and not in the other areas of the larger room). Key components are that there was little mixing of air with other sources (only the infrequent opening of the door at the other end of the large room) resulted in poor circulation and long duration exposure. A group that was only exposed for 18 minutes did not get sick. The waiters that came sporadically into the area did not get sick.
They did not say the size of the droplet nuclei that they used in their simulation.
This bodes well for my concern about being a few seconds behind someone on the street that coughs. Those are bigger droplets with more virus so you still want to avoid them, but maybe a single pass through such a cloud of virus might not be sufficient for infection.
RE: Aerosol transmission indoors - stupac2 - 04-25-2020
(04-25-2020, 10:57 AM)M T Wrote: This bodes well for my concern about being a few seconds behind someone on the street that coughs. Those are bigger droplets with more virus so you still want to avoid them, but maybe a single pass through such a cloud of virus might not be sufficient for infection.
Yeah, this is good confirmation but I think that we should have expected this to be the case just from infection numbers. If it were that easy to get it, we'd all have it by now.
RE: Aerosol transmission indoors - Snorlax94 - 04-25-2020
(04-25-2020, 11:32 AM)stupac2 Wrote:Yes, but I have found the data from these restaurant studies to be brobdingnagian. It emphasizes sustained contact with smaller droplets vs shorter exposure with larger droplets (as long as contact is not intimate, like hugging at a New Rochelle wedding or shaking hands at a Biogen conference). And it blows up the 6 foot rule.(04-25-2020, 10:57 AM)M T Wrote: This bodes well for my concern about being a few seconds behind someone on the street that coughs. Those are bigger droplets with more virus so you still want to avoid them, but maybe a single pass through such a cloud of virus might not be sufficient for infection.
Yeah, this is good confirmation but I think that we should have expected this to be the case just from infection numbers. If it were that easy to get it, we'd all have it by now.
It could provide a lot of guidance of how and what we should reopen. Maybe outdoor restaurant seating is key and indoor dining is surprisingly risky. Maybe many stores are reasonably safe (because the contact is not sustained, like for those waiters). When I can get a haircut (and cannot arrange for my stylist to cut my hair in my backyard), maybe I should pay full price but skip the shampoo to get in and out as fast as possible (again, more like a waiter instead of like a diner). Maybe all shops and restaurants should consider their airflows and we should shift cash registers outside as much as possible. Maybe workplaces like telemarketing firms and phone support with a bunch of workers packed together on the phone needs to be singled out as particularly dangerous. Maybe we’ve been emphasizing the wrong things, and less is spread via quick trips to shops and malls and more is spread via prolonged contact — business offices, meat processing plants, movie theaters, gyms, assembly lines, and garment shops. If sustained contact is key, it will be critical for counties and states to incorporate this into what can open, and how essential businesses like assembly lines need to change their operations.
RE: Aerosol transmission indoors - dabigv13 - 04-25-2020
You have to remember that these studies are feasible because they're trackable instances of transmission. If you catch it from a random jogger, you probably won't show up in a scientific study.
I do think that it's true that prolonged close contact is going to significantly increase transmission risk. That's how most respiratory viruses work too though, so no surprise.
RE: Aerosol transmission indoors - BostonCard - 04-25-2020
Another thing that bodes well for your theory is this paper.
https://www.medrxiv.org/content/10.1101/2020.04.04.20053058v1
They looked at 318 transmissions, and almost all happened at home or on transport. Only one chain, involving two cases, happened outdoor.
I haven’t had a lot of time to read the article in depth, but if true, you could pretty safely relax restrictions on outdoor activities, which Teejers sure would celebrate.
BC
RE: Aerosol transmission indoors - stupac2 - 04-25-2020
(04-25-2020, 04:46 PM)BostonCard Wrote: Another thing that bodes well for your theory is this paper.
https://www.medrxiv.org/content/10.1101/2020.04.04.20053058v1
They looked at 318 transmissions, and almost all happened at home or on transport. Only one chain, involving two cases, happened outdoor.
I haven’t had a lot of time to read the article in depth, but if true, you could pretty safely relax restrictions on outdoor activities, which Teejers sure would celebrate.
BC
At least around here restrictions on outdoor activities without shared equipment are already pretty loose. What's the research like around sharing something like a frisbee or golf cart? (Genuine question, I haven't seen any, and am skeptical that there's much transfer that way.) I'm also curious about, say, playground equipment (this is relevant to my interests, my kid doesn't usually want to use any of it but telling him to keep off when he does can cause headaches).
RE: Aerosol transmission indoors - M T - 04-25-2020
Another study: relating to outdoor exposure
Quote:Less attention has been paid to the spread of respiratory droplets in outdoor environments under microclimatologic turbulent wind...
[Simulation] Results show the spread of respiratory droplets is characterized by the dynamics of two groups of droplets of different sizes: larger droplets (400 – 900 μm) are spread between 2–5 m during 2.3 s while smaller (100 – 200 μm) droplets are transported a larger range between 8–11 m by the action of the turbulent wind in 14.1 s average.
I think the whole concept of "community transmission" is based on the transmissions that you can't find & track. We've had that in Santa Clara County since January apparently. So, just because you can say, "Here's 318 cases we can track" doesn't mean there aren't 5 or 500 cases you can't track, maybe because they were from shopping cart handles, the cough on the street, animal vectors, or what not.
I'm a bit disappointed we haven't seen more/better tracking of cases while we are in shelter in place. Just where are these cases coming from?
(or, maybe like deaths from COVID-19, we just have to wait longer for them to be researched & written)
Related to potential exposure rates:
A study about when were you last out of the house, and how close were you to others, associated by age.
Quote:About 52 percent of the adult United States population went out of their home the previous day. On average, adults had close contact with 1.9 non-household members. We find that having at least one COVID-19 symptom (fever, dry cough, or shortness of breath) increased the likelihood of going out the previous day and having additional close contacts with non-household members; however, the estimates were not statistically significant. When disaggregating our analysis by COVID 19 symptoms, we find no strong evidence of greater social distancing by people with a fever or cough in the last two weeks, but we do find that those who experienced shortness of breath have fewer close contacts, with an incidence rate ratio of 0.49 . Having other flu-like symptoms reduces the odds of going out by 0.32 and the incidence rate of having close contacts by 42 percent. We find that older people are just as likely to leave their homes as younger people, but people over the age of 50 had less than half the predicted number of close contacts than those who were younger than 30.Self-selection & other biases are noted.
And related to the above, California announced Friday that it would pay for delivery of restaurant meals to qualifying seniors "Restaurants Deliver: Home Meals for Seniors"