The experiment that proved airborne disease transmission

https://www.jhsph.edu/covid-19/articles/the-experiment-that-proved-airborne-disease-transmission.html

by pabo • 6 years ago

171 95 6 years ago

Can ultra-high resolution, ultra-high framerate and ultra-high zoom camera's measure exhalation of virii particles out of a humans mouth?

pvg• 6 years ago

Most viruses are smaller than visible light wavelengths. The biggest are about a wavelength or two.

Edit: some sizes here, including SARS-CoV-2

https://www.news-medical.net/health/The-Size-of-SARS-CoV-2-C...

praptak• 6 years ago

Resolution of plain optics only goes up to the diffraction limit, which is not enough to see a virus.

Then there are super-resolution techniques which can go beyond that, but I don't think any of them could be adapted to scan the vicinity of the coughing human in real time.

fulafel• 6 years ago

The virus is quite small and would have to be in some unconventional state to show up optically (could make an interesting what-if xkcd).

calibas• 6 years ago

It seems the reasoning by officials is, "Yes, it's airborne, but there's not enough N95 masks for everyone so we don't want to cause panic or an N95 mask shortage for doctors and nurses by admitting it's airborne."

dboreham• 6 years ago

Also supposedly if a disease is declared airborne then hospitals have to adopt various isolation measures beyond just N95 that are very costly. This may be the reason the powers that be won't announce airborne transmission until after the pandemic is over.

shalmanese• 6 years ago

We make fun of medieval medicine but look at this shit! We're pretending that saying some magic words has an effect on a physical reality of disease spread!

Who says that saying its airborne "has" to mean that certain procedures have to be adopted? That's not a rule of the universe, it's a rule that humans came up with and agreed upon and humans have the power to fix. We distilled down a set of physical principles into a set of guidelines, forgot the underlying physical principles and now operate purely in the world of the manmade guidelines, totally oblivious to when the guidelines are no longer reflecting the physical reality.

maxerickson• 6 years ago

It's useless to say this without evidence.

endgame• 6 years ago

Not the first time we were lied to as part of this disaster:

https://www.nytimes.com/2020/09/30/world/europe/ski-party-pa...

Turns out the "don't close borders" advice was a cached thought related to a plague outbreak in India over 25 years ago, and welded in place by politics.

throwmeaway_pls• 6 years ago

This culture of deceit needs to change. I don’t blame anybody for not following the rules.

mensetmanusman2• 6 years ago

It seems leaders think “you can’t handle the truth” is a proper response to citizens.

We would have had to prepare with 10 years of 24/6 manufacturing of N95s to stop an airborne virus, which is why the most effective response is social distancing (not going to work, the 6 ft thing is bunk).

lucb1e• 6 years 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

nostromo2• 6 years 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

ISL3• 6 years ago

In the same spirit, I offer Tami Knight's Avalanche Poodle: 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".

dehrmann4• 6 years ago

Same for lab rats.

contravariant• 6 years 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.2006.0962...

- 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• 6 years 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.

feralimal• 6 years 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.

trhway• 6 years ago

ultraviolet-C disinfection technology for air purification systems that were installed in health care facilities, factories, and NASA space capsules. Today, this technology is being used in Shanghai, Moscow, and New York City to protect subway and bus passengers against SARS-CoV-2, and China is also using the technology to disinfect hospitals

Russian FSB has just arrested (on secret state security charges) on his short trip back home from China a top high voltage systems specialist who has been working for the last two decades on UV water and air cleaning system in South Korea and China. Seems it is becoming a sought after hot tech in the current situation.

thaumasiotes• 6 years ago

Any kind of air cleaning is relevant, and in demand, in China.

Unfortunately, air purifiers have embraced the situation by demanding luxury pricing.

lifeisstillgood2• 6 years ago

UV-C lights that irradiate an air duct is literally the most surprising (and in retrospect obvious) thing I learnt today.

Is this something a household HVAC could be upgraded to. Do HNers in areas that have air con think it's a "yeah people will want that" idea?

TheSpiceIsLife• 6 years ago

What magnitude of irradiance is required?

If the required power is,say, 500w continues, or more, that's going to get quite expensive to run.

For example, where I live running a 500w device 24/7 is going to add an extra $1100 a year to the power bill.

tzs• 6 years ago

Looking at germicidal bulbs at 1000bulbs.com, the highest wattage bulb they have is 65 watts [1]. Most are well under that.

Looking at random in-duct systems, it looks like they range from 1 to 10 or so bulbs with the later being for commercial buildings. Home systems seem to lean toward 1 or 2 bulbs of maybe 20ish watts or so total. This site [2] says typically $15-30 per year energy cost

[1] https://www.1000bulbs.com/product/113917/AU-LG64T5L.html

[2] https://www.pickhvac.com/faq/hvac-uv-lights/

ajsnigrutin• 6 years ago

I always wondered just how much UV-C do you need to effectively kill the virus (power vs duct diameter and air speed).... because, instead of traditional masks, you could take a small fan, blow air into a pipe with a UV-C bulb inside, and pump the sterilized air to the human... basically something like this: https://www.youtube.com/watch?v=fzGrh2io9Ds&app=desktop

Gibbon1• 6 years ago

I tried looking into that this spring. I suspect the answer is for this virus not much. Nothing to indicate that any part of it's life cycle involves hanging around latent.

Interesting bit on how UV-C works to sterilize.

https://en.wikipedia.org/wiki/Pyrimidine_dimer

Interesting thing bacteria and some viruses have DNA repair enzymes that can fix damage from UV-C. Medically you're always bedeviled by bacterial and fungal spoors.

Limitations with UV-C sterilization I think prevents wider use. Not a magic bullet. Though it probably works well for influenza, colds, and this bat virus.

dehrmann4• 6 years ago

The real question is is there a safe wavelength and low enough power where you could swap out fluorescent tubes and effectively manage the virus.

xorcist• 6 years ago

It isn't very practical, as long as you don't worry about getting the virus from the outside in, which would be an unusual thing to worry about for home owners.

Just vent it out in the open air and not on people.

treis• 6 years ago

Just vent it out in the open air and not on people

Terrible for energy efficiency

dangrossman• 6 years ago

Any HVAC company can install this for you right now, or you can buy a kit and do it yourself. A UV light bulb to install in your central air system is an off the shelf product. "Whole house UV air purifier" as a search term will pull these up.

fyfy18• 6 years ago

Are these products actually effective though? I mean the duration and intensity required to kill viruses in moving air must be quite high? Or is it just snake oil, like how a lot of hand dryers have bluish/purple LEDs (which emit no UV) that shine on your hands?

nostromo2• 6 years ago

It's important to remember that your immune system is improved by coming in contact with common viruses. This is even more important for kids.

There's evidence that people that have been exposed to previous, weaker, coronaviruses are more likely to have mild responses to Covid-19, for example.

https://science.sciencemag.org/content/370/6512/89

femto• 6 years ago

If DIYing, choose your UV wavelength wisely. UVC (around 254nm wavelength) is germicidal and doesn't produce ozone (it actually dissociates ozone). "Vacuum UV" (in the range 185nm) converts oxygen in the air to ozone, which is highly toxic.

[1] http://www.uvresources.com/blog/the-ultraviolet-germicidal-i...

dehrmann4• 6 years ago

Also the whole skin cancer thing.

apaprocki• 6 years ago

There are plenty of products for both HVAC and plumbing that use UV-C. The new hotness is 405nm because it’s safe around humans and there are already under cabinet lights for kitchens and overhead recessed lights for bathrooms, etc.

amluto• 6 years ago

Nope. I would much rather have a good filter than mechanically removes infectious particles, wildfire smoke, and particulates in general.

For a residential recirculating system, the relevant parameter is flow rate times fraction of particles removed in one pass. An AC or heater generally has a high flow rate and needs a filter to keep the heat exchanger and fan clean regardless. The added material and energy cost of a good filter is low.

On the other hand, if you are moving air from one space to another and don’t want to contaminate the space you’re moving air to, the absolute filter / sterilizer efficiency may matter. Things like HEPA may be useful here.

I would be surprised if a UV lamp is cost effective for new installation. For retrofit in a system that can’t handle a better filter, maybe.

31337• 6 years ago

Germicidal irradiation via UV light on HVAC is just not possible. Due to the amount of energy it requires to be effective is ridiculously high.

https://www.climask.com.tr is interesting. Like a face mask on AC unit. Nano-silver is effective against bacterias and viruses. And having a filter with nano-silver coated surface is just a simple yet an effective approach. Cost-wise changing a good quality air filter every 2-3 months is much cheaper than having a UVGI installed and paying higher electricity bill every month.

ajb2• 6 years ago

Ok, dumb idea time: suppose that everyone in an office sits on a chair that raises their body to X volts. At the same time a collector mesh is provided at each desk, at -X volts, but shielded so that you can't touch it and shock yourself.

What X is large enough to ensure that all the virus particles you cough out end up at the collector? Is it possible to do this without electrocuting everyone?

vimax• 6 years ago

that sounds kind of like what an ionized air purifier does

imposterr• 6 years ago

Free electrons tend to distribute themselves on an object as to minimize the repulsive forces between them. This usually means that they distribute evenly on the surface of objects.

Humans are a bit more complicated in structure than say a metal ball, but my guess would be that there would be a similar situation where all the free electrons would just build up on the skin. Therefore, I don't think the particles one would cough up would be negatively charged.

enchiridion• 6 years ago

Would the particles get charged as they pass through the later of electrons?

curryst• 6 years ago

Alveoli are basically small air sacs in your lungs, so they're a surface (it's just an inverted ball, a hollow sphere in a not-so-solid object).

No idea how that influences where the electrons go.

I wonder how the nervous system would interact with that as synapses fire. I'm curious if they would build up, or if the synapses all over the body firing would make them bounce around constantly.

computator• 6 years ago

This seems to assume that virus particles are charged. If they are neutral, they wouldn't be driven in any direction by an electric field. Am I missing something? Is it known that virus particles have a charge?

nkurz• 6 years ago

I think you are missing the OP's assumption that by raising the subject's entire body to +X Volts, any virus particles they breath out will start out with this same positive charge. I'm not sure this assumption is true, but it seems plausible.

R0b0t12• 6 years ago

Particles in the air respond to charges. https://en.wikipedia.org/wiki/Electrostatic_precipitator

ISL3• 6 years ago

X depends upon the distance between people. (and upon the propensity for the exhaled particles to be neutralized)

saalweachter3• 6 years ago

The mass difference between humans and viruses is something like 10^19.

So if you take the naive approach -- which is wrong, because charges live on surfaces, not in volumes -- you would want the person to have about a coulumb of charge to ensure that 1 extra electron was allocated to each virus particle.

Whether or not 1 electron per virus is enough is a separate question, but that gives you a lower bound -- if you are allocating, say, 0.1 electrons, only 10% of your virus particles will have a charge.

Edit: so, given the capacitance of humans as 200 pF, that would be 5 gigavolts?

Apofis• 6 years ago

Somebody get Elon on the horn, we have the world to save!

ajb2• 6 years ago

Wow, okay - that explains why we're not doing this already!

I'm curious as to why this logic doesn't apply to the electrostatic precipitator. Or maybe it does and we just have too much capacitance?

https://en.m.wikipedia.org/wiki/Electrostatic_precipitator

ETA: the EP causes Corona discharge, which doesn't sound like it would be too pleasant if you were the electrode.

Aerroon• 6 years ago

I'm actually curious: how many 'virus particles' does a person need to be exposed to on average to contract the virus?

heavenlyblue• 6 years ago

Wouldn’t viruses fly away so your 0.1 electrons is only true for the first batch of viruses to depart?

R0b0t12• 6 years ago

You don't need to raise the person's potential for this to work, though it could make it more effective. https://en.wikipedia.org/wiki/Electrostatic_precipitator

Places like hospitals filter the air internally to reduce infection.

praveen9920• 6 years ago

Can we "mutate" a virus to use radioactive isotope of carbon (c-14? something that is not harmful for humans) so that we can observe how viral a virus is?

Not an expert on radio isotopes or spectrography or viruses.

Note: I know, radioactive virus at this point might freakout people a little.

koeng• 6 years ago

AFAIK there aren’t methods to do that in vivo, unfortunately.

ISL3• 6 years ago

No need. It mutates itself. The propagation of genetic strains of Covid-19 can be viewed here:

https://nextstrain.org/ncov/global

Our ability to do this for every single Covid-19 case in the universe is, I imagine, limited only by funding/infrastructure/training.

globular-toast2• 6 years ago

Where would it get the carbon-14 from? Virus particles (virions) are made by and from their host. So you'd need a human made from carbon-14 first.

Jabbles3• 6 years ago

We basically already know how viral viruses are because they undergo mutations, and we can trace which strain people have and where they caught it from by sequencing their DNA (technically RNA) and looking for the virus's "ancestors".

See for example https://www.eurekalert.org/pub_releases/2020-10/du-gt100120....

Also you wouldn't mutate a virus with C14 or similar radiactive isotope, because that can't be encoded in its genetics, and such a virus would use any old Carbon atom (most likely normal C12) to replicate.

Finally, mutating a virus and releasing it seems ethically dubious in the middle of a pandemic...

lootsauce• 6 years ago

Ok dumb question why don’t we settle the question by conducting the experiment for covid19?

hurrynot• 6 years ago

The article says the TB experiment ran for four years. It isn't clear that you need four years to prove airborne transmission, but it is likely that you need a lot of time.

RogerKamben• 6 years ago

It's pretty much settled also for sars-cov2. A study in China found the virus in air samples taken inside the central air-condition system, far away from any patients (see bottom). Another found correlation between infected and where they were sitting vs AC duct outlets.

Also the fact that mandatory masks have had zero effect on the R value in any country, same as for influenza and other "flu" viruses. If it was spread by droplets/surfaces then masks should at least have some effect to slow or contain the spread, like make a dent in the curves.

Yes there are masks that prevent TB transmission but this bacteria is more than 10x larger than typical respiratory viruses. They look like duck beaks, are very uncomfortable and require training to use properly. I haven't seen these anywhere during this pandemic and they wouldn't help either as they are designed to prevent aerosols down to about 2um size. There is plenty of space for ~0.1um viruses even in 0.5um droplets. Some researchers even claim the virus can stay potent a while after the droplet evaporates and float around like dust.

CDC meta study showing medical masks had no effect neither as PPE or source control: https://wwwnc.cdc.gov/eid/article/26/5/19-0994_article Study comparing medical masks and N95 masks found no difference in transmission of influenza: https://pubmed.ncbi.nlm.nih.gov/31479137/ More links and summaries collected here: https://swprs.org/face-masks-evidence/ This Time article has lots of links and info (but the argument for masks is complete fail): https://time.com/5883081/covid-19-transmitted-aerosols/

It's funny how some claim we didn't need masks before, but now we need them since it's spread by aerosols?? The truth is in fact the opposite and don't get me started on cloth masks...it's absurd. This seems more like covering their asses than following the science.

Most of these studies involve health personell, with high-end masks, the general public will of course do much much worse. This survey of studies and history of mask use in dentistry is also informative (why was it taken down?): https://archive.is/My2jr

The WHO reversal on mask use is also revealing: On July 12, Deborah Cohen, the medical correspondent of BBC2’s Newsnight, revealed on Twitter that: ‘We had been told by various sources [that the] WHO committee reviewing the evidence had not backed masks but they recommended them due to political lobbying.’ She said the BBC had then put this to the WHO, which did not deny it. In March, the WHO had said: ‘There is currently no evidence that wearing a mask (whether medical or other types) by healthy persons in the wider community setting, including universal community masking, can protect them from infection with respiratory viruses, including Covid-19.’

-Van Doremalen N, Bushmaker T, Morris DH, Holbrook MG, Gamble A, Williamson BN, et al. Aerosol and surface stability of SARS-CoV-2 as compared with SARS-CoV-1. N Engl J Med. 2020;382:1564-7. -Fears AC, Klimstra WB, Duprex P, Weaver SC, Plante JA, Aguilar PV, et al. Persistence of Severe Acute Respiratory Syndrome Coronavirus 2 in Aerosol Suspensions. Emerg Infect Dis 2020;26(9). -Chia PY, for the Singapore Novel Coronavirus Outbreak Research T, Coleman KK, Tan YK, Ong SWX, Gum M, et al. Detection of air and surface contamination by SARS-CoV-2 in hospital rooms of infected patients. Nat Comm. 2020;11(1). -Guo Z-D, Wang Z-Y, Zhang S-F, Li X, Li L, Li C, et al. Aerosol and Surface Distribution of Severe Acute Respiratory Syndrome Coronavirus 2 in Hospital Wards, Wuhan, China, 2020. Emerg Infect Dis. 2020;26(7). -Santarpia JL, Rivera DN, Herrera V, Morwitzer MJ, Creager H, Santarpia GW, et al. Transmission potential of SARS-CoV-2 in viral shedding observed at the University of Nebraska Medical Center (pre-print). MedRxiv. 2020 doi: 10.1101/2020.03.23.20039446. -Zhou J, Otter J, Price JR, Cimpeanu C, Garcia DM, Kinross J, et al. Investigating SARS-CoV-2 surface and air contamination in an acute healthcare setting during the peak of the COVID-19 pandemic in London (pre-print). MedRxiv. 2020 doi: 10.1101/2020.05.24.20110346. -Liu Y, Ning Z, Chen Y, Guo M, Liu Y, Gali NK, et al. Aerodynamic analysis of SARS-CoV-2 in two Wuhan hospitals. Nature. 2020;582:557-60. -Ma J, Qi X, Chen H, Li X, Zhan Z, Wang H, et al. Exhaled breath is a significant source of SARS-CoV-2 emission (pre-print). MedRxiv. 2020 doi: 10.1101/2020.05.31.20115154. -https://pubmed.ncbi.nlm.nih.gov/19797474/ -https://pubmed.ncbi.nlm.nih.gov/19216002/

Jabbles3• 6 years ago

The meta study does not "[show] medical masks had no effect", it shows that we have limited evidence for it:

"Most studies were underpowered because of limited sample size, and some studies also reported suboptimal adherence in the face mask group"

https://wwwnc.cdc.gov/eid/article/26/5/19-0994_article

And indeed you can sympathise with them that it would be hard to perform such an experiment.

But the whole point of science is that it allows us to make predictions based on theories. And the current scientific consensus is that wearing masks is beneficial.

mensetmanusman2• 6 years ago

Scientists have already published work confirming the virus is airborne stable and viable for many hours.

I don’t know why there hasn’t been more discussions about the consequences of this though.

For example, with airborne transmission, 6 ft distance is not enough, you need > 30 ft, e.g. if you are inside with poor airflow for a long time with someone who is infected, good luck (unless you have a good N95).

dmix• 6 years ago

This quote from the report should be top of the list of the lesson-learned from this COVID pandemic:

The current guidance from numerous international and national bodies focuses on hand washing, maintaining social distancing, and droplet precautions. Most public health organizations, including the World Health Organization (WHO) [16], do not recognize airborne transmission except for aerosol-generating procedures performed in healthcare settings. Hand washing and social distancing are appropriate but, in our view, insufficient to provide protection from virus-carrying respiratory microdroplets released into the air by infected people. This problem is especially acute in indoor or enclosed environments, particularly those that are crowded and have inadequate ventilation [17] relative to the number of occupants and extended exposure periods (as graphically depicted in Figure 1). For example, airborne transmission appears to be the only plausible explanation for several superspreading events investigated that occurred under such conditions [10], and others where recommended precautions related to direct droplet transmissions were followed.

Indoor contact, proper veneration, etc causing super-spreader events.

Meanwhile here in Canada they waited until late May to even recommend wearing a mask in such situations (other countries like the US had similar time frames and Dr Fauci openly admitted they withheld this recommendation for the benefit of healthcare workers).

https://www.ctvnews.ca/politics/it-s-now-recommended-that-ca...

Much like drug prohibition and other grand social control experiments, I'm not convinced the value of being vague or simply straight up not recommending masks in order to keep supply chain available for healthcare workers was ultimately worth the downside.

If supply chains was the issue then spend the government law enforcement power controlling and directing the supply chain for medical quality masks. This 4 month experiment (and I'm being generous there) where Feb, Mar, Apr and most of May they spent creating confusion and not recommending masks ultimately did more harm than good.

Now pundits and online commenters love to attack these anti-mask people when for much of the year expert sources were far from making masks the recommended choice. Including gov-delivered misinformation about their utility in order to explain themselves.

If the pro-social control (ie, lying the public) group thinks it was really stopping the wealthy and connected from completely ignoring these guidelines, then they are lying to themselves. As always with these gov poppet-mastery policies the only losers were the lowest common denominator poor people. Plenty of which still don't funny trust masks.

I would have rather spent four+ months explaining the virtues of masks and explaining the supply problem honestly. Than playing catch up last minute.

The fact Asia who had adopted masks, and never spent any time lying or dodging their public on their utility, have done better than western countries is no surprise. Asian countries had masks well before COVID.

The older I get the more cynical I become about government and intelligentsia 'we know whats best', that includes withholding information (something extra popular in healthcare). All information should be as transparent as possible, regardless of fantasies of controlling it.

tech6• 6 years ago

I have an ozone vegetable washer. Is it dangerous to be in same room when this vegetable washer is running ? I can smell the odour of ozone near the vegetable washer

ficklepickle• 6 years ago

The odour detection threshold is 0.005-0.02 PPM. OSHA says less than 0.1 PPM over an 8-hour period.

So you can smell ozone well before it is in the harmful range. Some air circulation wouldn't hurt while the device operates, but napkin math says you are OK.

pbreit• 6 years ago

Was there any doubt?

globular-toast2• 6 years ago

Yes. A very quick, less than a minute, skim of the article would tell you that.

pa7x1• 6 years ago

The idea of respiratory viruses not being airborne sounds silly. What's the viral charge supposed to do, not jump into droplets smaller than certain size?

Of course they are present in the smallest droplets! They are present in the mucous secretions of the infected individual and they will get expelled through the big and the small droplets.

The distinction shouldn't be a qualitative one, airborne vs not airborne. It's a quantitative one, sufficiently infectious viruses may pose a risk at much smaller doses, the kind that you may be exposed by the smallest droplets expelled that simply stay afloat.

It's also worth noting that human immune response is a complicated beast, what may not be infectious for an average healthy individual may put down someone with a weakened immune response. So even supposedly "not airborne" viruses that are very unlikely to infect the average healthy individual at very small doses may pose an "airborne" risk for individuals with a weakened immune response.

There are more factors in all of this, atmospheric conditions may play a role. For example, cold temperatures may be more suitable for the virus to remain infectious outside of a host, thus increasing the likelihood of "airborne" propagation.

TL;DR: The distinction between airborne and not airborne viruses is an artificial one. That only makes sense statistically for an average individual at certain atmospheric conditions for a concrete strain of the virus. But as any real-world statistical distribution there are tails and you will find "airborne" qualities for pretty much any respiratory virus in those tails.

The experiment that proved airborne disease transmission

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