6 ms·

TL;DR: the actual experiment: > they constructed an air-tight closed ventilation system that connected a six-room tuberculosis ward to an exposure chamber with

by lucb1e 6y ago

TL;DR: the actual experiment: > they constructed an air-tight closed ventilation system that connected a six-room tuberculosis ward to an exposure chamber with 150 guinea pigs. (Among rodent animal models, only guinea pigs could cough and sneeze, making them ideal for studying how respiratory diseases spread.) The guinea pigs were exposed to the infected air over a four-year period. A second group of 150 guinea pigs acted as controls: their air ducts were irradiated with UV-C lamps to kill TB bacilli. Results: > an average of three guinea pigs per month contracted TB, while no controls were infected. The experiment [also] quantified how many TB infections could be expected to result from exposure to a given number of patients over a defined interval. Relevance to COVID-19: > Riley’s research points to wearing masks and disinfecting air in enclosed spaces as two of the most effective tools for fighting COVID-19

nostromo 6y ago
Today I learned: > The animals were used so frequently as model organisms in the 19th and 20th centuries that the epithet guinea pig came into use to describe a human test subject. https://en.wikipedia.org/wiki/Guinea_pig https://en.wikipedia.org/wiki/Guinea_pig
- ISL 6y ago
  In the same spirit, I offer Tami Knight's Avalanche Poodle: https://www.snowmediazone.com/the_zone/data/500/medium/Avi_poodle.jpg https://www.snowmediazone.com/the_zone/data/500/medium/Avi_p... Among my friends, to go first in an uncertain situation is sometimes called, "poodling it".
- dehrmann 6y ago
  Same for lab rats.
contravariant 6y ago
Some things worth pointing out about the linked article (not by Riley), regarding masks and disinfecting air: https://ajph.aphapublications.org/doi/10.2105/AJPH.2006.096214 https://ajph.aphapublications.org/doi/10.2105/AJPH.2006.0962... - It contains no experimental data, it's a review of possible methods. - It's not about Covid-19, although that's to be expected. - The masks it talks about are N95 and N100 respirators (which it notes aren't in adequate supply). Some interesting quotes: > If one assumes that influenza is transmitted by respiratory droplets [..] rather than by aerosols [..], the supposition may be that keeping a safe distance may obviate the need for a mask. It is stated that the range of such droplets is generally no more than 3 ft. We are unable to locate the basic science behind that assertion. > Whether contagious as a respiratory droplet, aerosol, or both, there have been no controlled studies to investigate the efficacy of respirators in preventing the transmission of influenza A > there is a theoretical problem in the logic underlying N–95 respirators. Assume an N–95 mask functions better than its rating and at a sedentary inhalation rate blocks 98% of the bioaerosols that it is confronted with. We are still left with the 2% that penetrate through the filter, to be inhaled by the wearer. Whether discussing tuberculosis, influenza, measles, or smallpox, we do not know the concentration of pathogenic bioaerosols in the environment, nor do we know the minimum infectious dose for these pathogens. Anyway I don't think anyone disagrees with their conclusion that having everyone wear N100 masks is a good idea, but I'm not sure if any of their proposed methods are feasible. And the most important conclusion of their research is perhaps that we know way too little about possible countermeasures.
- neilwilson 6y ago
  The logic is short in other terms. It requires you wear the mask at all times. And that you change it regularly by removing folding inwards and disposing securely. Otherwise you may pick up an infection and then put a mask on afterwards which necessarily means that much of the shedding caught in the mask will be breathed back in - From mouth to nose and vice versa. Or put the mask back on backwards or wave it around in the air, put it on surfaces and the like. All of which amplify the current infection you have making you more infectious when you take the mask off. And may explain why at a local Covid secure school they all went down with the usual back to school viral cold far more rapidly this year than they normally do. What we don’t know - because we’re not hamsters permanently in cages - is what the network effects are.
  - dehrmann 6y ago
    For all the talk about how much masks help, I haven't seen great studies that aren't in vitro, not specifically in health care settings, and not specifically around someone known to have it. I found this which is at least a natural experiment: https://www.healthaffairs.org/doi/pdf/10.1377/hlthaff.2020.00818 https://www.healthaffairs.org/doi/pdf/10.1377/hlthaff.2020.0... > Mandating face mask use in public is associated with a decline in the daily COVID-19 growth rate by 0.9, 1.1,1.4, 1.7, and 2.0 percentage points in 1–5, 6–10, 11–15, 16–20, and 21 or more days after state face mask orders were signed, respectively. I'm trying to sort of if those percentages are absolute or relative. I think they're absolute because some of the graphs are labeled "percentage point change," but using absolute percentage point changes for an analysis like this is seriously flawed because a 2% reduction could range anywhere from a miracle to statistically significant, but negligible. It's also not clear if people feel safer wearing face masks, so they engage in riskier activities. My guess is they're not as effective as claimed because while the Bay Area has pretty high compliance, if masks were systemically very effective, we'd see case rates drop a lot faster, not still be above mid-June numbers. That said, whatever the Bay Area is doing right now is working.
deleted 6y ago
[deleted]
feralimal 6y ago
From this experiment you might say something about disinfecting air, but the guinea pigs weren't wearing masks. What you are testing, if anything, is the efficacy of "UV-C lamps to kill TB bacilli". Wearing masks is an entirely different thing, and would need an entirely different test. Even the original experiment leaves questions for me. How does one diagnose TB in guinea pigs? What health state were the guinea pigs in? Was there a familial predisposition to respiratory illnesses for some of these? What conditions were they kept in? Etc.

by lucb1e 6y ago

nostromo 6y ago

Today I learned: > The animals were used so frequently as model organisms in the 19th and 20th centuries that the epithet guinea pig came into use to describe a human test subject. https://en.wikipedia.org/wiki/Guinea_pig https://en.wikipedia.org/wiki/Guinea_pig

ISL 6y ago
In the same spirit, I offer Tami Knight's Avalanche Poodle: https://www.snowmediazone.com/the_zone/data/500/medium/Avi_poodle.jpg https://www.snowmediazone.com/the_zone/data/500/medium/Avi_p... Among my friends, to go first in an uncertain situation is sometimes called, "poodling it".
dehrmann 6y ago
Same for lab rats.

contravariant 6y ago

Some things worth pointing out about the linked article (not by Riley), regarding masks and disinfecting air: https://ajph.aphapublications.org/doi/10.2105/AJPH.2006.096214 https://ajph.aphapublications.org/doi/10.2105/AJPH.2006.0962... - It contains no experimental data, it's a review of possible methods. - It's not about Covid-19, although that's to be expected. - The masks it talks about are N95 and N100 respirators (which it notes aren't in adequate supply). Some interesting quotes: > If one assumes that influenza is transmitted by respiratory droplets [..] rather than by aerosols [..], the supposition may be that keeping a safe distance may obviate the need for a mask. It is stated that the range of such droplets is generally no more than 3 ft. We are unable to locate the basic science behind that assertion. > Whether contagious as a respiratory droplet, aerosol, or both, there have been no controlled studies to investigate the efficacy of respirators in preventing the transmission of influenza A > there is a theoretical problem in the logic underlying N–95 respirators. Assume an N–95 mask functions better than its rating and at a sedentary inhalation rate blocks 98% of the bioaerosols that it is confronted with. We are still left with the 2% that penetrate through the filter, to be inhaled by the wearer. Whether discussing tuberculosis, influenza, measles, or smallpox, we do not know the concentration of pathogenic bioaerosols in the environment, nor do we know the minimum infectious dose for these pathogens. Anyway I don't think anyone disagrees with their conclusion that having everyone wear N100 masks is a good idea, but I'm not sure if any of their proposed methods are feasible. And the most important conclusion of their research is perhaps that we know way too little about possible countermeasures.

neilwilson 6y ago
The logic is short in other terms. It requires you wear the mask at all times. And that you change it regularly by removing folding inwards and disposing securely. Otherwise you may pick up an infection and then put a mask on afterwards which necessarily means that much of the shedding caught in the mask will be breathed back in - From mouth to nose and vice versa. Or put the mask back on backwards or wave it around in the air, put it on surfaces and the like. All of which amplify the current infection you have making you more infectious when you take the mask off. And may explain why at a local Covid secure school they all went down with the usual back to school viral cold far more rapidly this year than they normally do. What we don’t know - because we’re not hamsters permanently in cages - is what the network effects are.
- dehrmann 6y ago
  For all the talk about how much masks help, I haven't seen great studies that aren't in vitro, not specifically in health care settings, and not specifically around someone known to have it. I found this which is at least a natural experiment: https://www.healthaffairs.org/doi/pdf/10.1377/hlthaff.2020.00818 https://www.healthaffairs.org/doi/pdf/10.1377/hlthaff.2020.0... > Mandating face mask use in public is associated with a decline in the daily COVID-19 growth rate by 0.9, 1.1,1.4, 1.7, and 2.0 percentage points in 1–5, 6–10, 11–15, 16–20, and 21 or more days after state face mask orders were signed, respectively. I'm trying to sort of if those percentages are absolute or relative. I think they're absolute because some of the graphs are labeled "percentage point change," but using absolute percentage point changes for an analysis like this is seriously flawed because a 2% reduction could range anywhere from a miracle to statistically significant, but negligible. It's also not clear if people feel safer wearing face masks, so they engage in riskier activities. My guess is they're not as effective as claimed because while the Bay Area has pretty high compliance, if masks were systemically very effective, we'd see case rates drop a lot faster, not still be above mid-June numbers. That said, whatever the Bay Area is doing right now is working.

deleted 6y ago

[deleted]

feralimal 6y ago

From this experiment you might say something about disinfecting air, but the guinea pigs weren't wearing masks. What you are testing, if anything, is the efficacy of "UV-C lamps to kill TB bacilli". Wearing masks is an entirely different thing, and would need an entirely different test. Even the original experiment leaves questions for me. How does one diagnose TB in guinea pigs? What health state were the guinea pigs in? Was there a familial predisposition to respiratory illnesses for some of these? What conditions were they kept in? Etc.