health

Pandemic exposes scientific rift over proving when germs are airborne

14 Comments
By Julie Steenhuysen

The coronavirus pandemic has exposed a clash among medical experts over disease transmission that stretches back nearly a century - to the very origins of germ theory.

The Geneva-based World Health Organization acknowledged last week that the novel coronavirus can spread through tiny droplets floating in the air, a nod to more than 200 experts in aerosol science who publicly complained that the U.N. agency had failed to warn the public about this risk.

Yet the WHO still insists on more definitive proof that the novel coronavirus, which causes the respiratory disease COVID-19, can be transmitted through the air, a trait that would put it on par with measles and tuberculosis and require even more stringent measures to contain its spread.

"WHO's slow motion on this issue is unfortunately slowing the control of the pandemic," said Jose Jimenez, a University of Colorado chemist who signed the public letter urging the agency to change its guidance.

Jimenez and other experts in aerosol transmission have said the WHO is holding too dearly to the notion that germs are spread primarily though contact with a contaminated person or object. That idea was a foundation of modern medicine, and explicitly rejected the obsolete miasma theory that originated in the Middle Ages postulating that poisonous, foul-smelling vapors made up of decaying matter caused diseases such as cholera and the Black Death.

"It's part of the culture of medicine from the early 20th century. To accept something was airborne requires this very high level of proof," said Dr. Donald Milton, a University of Maryland aerobiologist and a lead author of the open letter.

Such proof could involve studies in which laboratory animals become sickened by exposure to the virus in the air, or studies showing viable virus particles in air samples - a level of proof not required for other modes of transmission such as contact with contaminated surfaces, the letter's signatories said.

For the WHO, such proof is necessary as it advises countries of every income and resource level to take more drastic measures against a pandemic that has killed more than 550,000 people globally, with more than 12 million confirmed infections.

For example, hospitals would have to provide more healthcare personnel with heavy-duty N95 respiratory masks - personal protective gear already in short supply - and businesses and schools would need to make improvements to ventilation systems and require wearing masks indoors at all times.

"It would affect our entire way of life. And that's why it's a very important question," said Dr. John Conly, a University of Calgary infectious disease expert who is part of the WHO's group of experts advising on coronavirus guidelines.

Conly said that so far the studies have not shown viable virus particles floating in the air.

"In my mind, I want to see evidence in those fine mists," Conly said.

HOW FAR CAN A DROPLET TRAVEL?

The WHO's latest guidance document, released on Thursday, called for more research on coronavirus aerosol transmission, which it said "has not been demonstrated."

The agency also repeated a firm cutoff on the size of infectious droplets expelled in coughing and sneezing, noting that most larger droplets are unlikely to travel beyond one meter (3.3 feet) - the basis for their one-meter social distancing guidelines. Milton and others have said larger particles have been shown to spread much farther.

Conly and others maintain that if the virus were truly airborne like measles, there would already be many more cases.

"Would we not be seeing, like, literally billions of cases globally? That's not the case," Conly said.

WHO spokeswoman Dr. Margaret Harris rejected the claim by critics that the agency is biased against idea of aerosol transmission, saying it recognized the possibility of airborne transmission during medical procedures from early on in the pandemic.

Harris said it is "quite possible" that aerosolization is a factor in some so-called super-spreading events in which one infected person infects many others in close quarters. Many of these events have occurred in places such as nightclubs where people are packed together and are not likely to be careful about protecting themselves or others from infection.

"Most super-spreading events have occurred in indoor places with poor ventilation, with crowding, where it's very difficult for people to socially distance," Harris said.

That is why, Harris said, the agency has called for urgent studies to figure out "what really happened in these clusters and what were the big factors."

© Thomson Reuters 2020.

©2020 GPlusMedia Inc.

14 Comments
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The article makes it seem as if there were only two opinions, that it is impossible to happen in any circumstance or that it is responsible for the majority of the cases. In reality it is not so.

The difference of opinion is only about how important this is for the current pandemic. Like every other infectious respiratory disease covid-19 has been very likely transmitted by aerosols, at least in some cases; but for the purposes of public health policy there is no evidence (yet?) that aerosols contribute to the spreading more often than just very rarely. This is important because measures against aerosols are much more costly and difficult, so recommending to do them could have a counterproductive effect.

If for example it becomes clear that 1 out of 10 infections are due to aerosols it would mean that there is no other way to control thee spreading and terribly strict measures would have to be put in place. But if evidence points out to 1 out of 10,000 cases being due to aerosols then there is no real point in spending a huge lot more of resources to stop only a few more cases.

6 ( +6 / -0 )

Even if actual airborne transmission is minimal source control is still very important because virus is primarily transmitter via respiratory droplets.

If the general population is wearing masks droplets infecting surfaces can be kept to a minimum

-4 ( +0 / -4 )

Limited resources shouldn't be used as reason to limit use of masks and other ppe if there's evidence they're useful.

Entire economies have been shut down and sacrificed because of covid19, only a tiny fraction of that is needed to ensure adequate supply.

-2 ( +0 / -2 )

Even if actual airborne transmission is minimal source control is still very important because virus is primarily transmitter via respiratory droplets.

Airborne transmission is different from transmission by droplets. Wearing a mask is enough to importantly reduce transmission by droplets, but have minimal if any effect on aerosols.

If airborne transmission is minimal it simply do not justify investing all the resources necessary to deal with it, specially because it would mean the simple and effective measures against droplets would have to be reduced. In order to prevent one extra case you would expend the resources that right now prevent a thousand of them.

Limited resources shouldn't be used as reason to limit use of masks and other ppe if there's evidence they're useful.

Considering important airborne transmission would precisely mean to limit the use of mask and other ppe, because it would have no effect on it. Economies would have to shut down much more strictly and for longer time because isolation is the only measure that would actually be effective, and a much larger fraction of resources would be necessary to obtain the much higher degree of complexity for the ppe that is actually effective against aerosols.

For example instead of being able to buy 200 reusable coverall suits at $5, hospitals would need to buy one single hermetic and pressurized suit at $1000. That is why it is necessary to carefully determine if the transmission is by aerosols or by droplets.

2 ( +3 / -1 )

Even if actual airborne transmission is minimal source control is still very important because virus is primarily transmitter via respiratory droplets.

Airborne transmission is different from transmission by droplets. Wearing a mask is enough to importantly reduce transmission by droplets, but have minimal if any effect on aerosols.

Yes, that's why I don't understand bthe reluctance ofvthe WHO to prescribe use of masks and actually discourage it given viadroplets is significant mode of transmission

-3 ( +0 / -3 )

I understand the great additional cost of having to use additional and much more complex /higher rated ppe, my contention is it should no longer be an issue now that more drastic and costly measures ie business lockdowns are routinely and immediately implemented by governments.

The limiter should be production capacity, not cost anymore.

-2 ( +0 / -2 )

Quite agree there needs to be more research to determine if and to what degree there may be transmission by aerosol.

Knee jerk reaction is not helpful and can be actually damaging.

0 ( +0 / -0 )

Too late for that. The usual knee jerk reaction now is the most costly of all, lockdowns, reaction of course due to the many uncertainties about the virus.

Transmission by droplets is not one of those uncertainties though

-1 ( +0 / -1 )

Yes, that's why I don't understand bthe reluctance ofvthe WHO to prescribe use of masks and actually discourage it given viadroplets is significant mode of transmission

You don't understand because it is not true, the WHO has been recommending the use of masks even if the person is completely asymptomatic.

it should no longer be an issue now that more drastic and costly measures ie business lockdowns are routinely and immediately implemented by governments.

Lockdowns would also become more strict and longer lasting. even escencial business like supermarkets would become unacceptably dangerous if aerosols are an important form of transmission. What you have not yet understood is that It would not mean changing one drastic measure on some parts and the same in another, it would mean a more strict way to do things all around, from personal protection to economic lockdown.

The usual knee jerk reaction now is the most costly of all, lockdowns, reaction of course due to the many uncertainties about the virus.

You would need data to be able to qualify as knee jerk reaction something that proved extremely useful at interrupting transmission, so much that in many places it is being considered again. That still applies without aerosol transmission.

1 ( +1 / -0 )

> Yes, that's why I don't understand bthe reluctance ofvthe WHO to prescribe use of masks and actually discourage it given viadroplets is significant mode of transmission

You don't understand because it is not true, the WHO has been recommending the use of masks even if the person is completely asymptomatic.

I was referring to the recommendation before, when use for general population was discouraged. Im not even sure if that has changed already

-2 ( +0 / -2 )

And I don't know what data you need to qualify knee jerk reaction. To qualify that a lockdown is not very useful? I wasn't aware that knee jerk reaction needs to be that to be considered nor I dispute that lockdowns aren't effective at controlling infection.

-2 ( +0 / -2 )

Anyway my concern primarily is about the use of masks to control droplets, I think that's clear enough from my initial post.

And why cost shouldn't be a concern considering it seems to be ok to use much more costly interventions.

Thanks for the explanations though I've learned a lot

-2 ( +0 / -2 )

Correct me if I am wrong:

Our understanding so far is that airborne transmission is predominantly, though not exclusively, limited by proximity. That is why social distancing and masks are so important.

Also, of prime concern is transmission by physical contact, which is why gloves, social distancing, and hand washing are so important.

The question about airborne transmission over longer distances seems to be that it is possible, but less likely outdoors than indoors.

As for testing and quarantine measures, they also are and should be part of the tool kit for response.

Last but not least, the wonderful efforts made by hospital staffs to save lives.

2 ( +2 / -0 )

I was referring to the recommendation before, when use for general population was discouraged. Im not even sure if that has changed already

It has, from a long time ago, that is why I am telling you you are wrong. You know knowing something available on the news for anybody only explains why you are wrong.

And I don't know what data you need to qualify knee jerk reaction. To qualify that a lockdown is not very useful? I wasn't aware that knee jerk reaction needs to be that to be considered nor I dispute that lockdowns aren't effective at controlling infection.

Yes it is necessary, the expression is meant for a reaction done without thinking, without considering anything like evidence or rational steps. Lockdowns were carefully considered and had the expected results when done properly and strictly, just as the scientific data behind that decision predicted.

Let me be more clear, reacting quickly is not equal to a knee jerk reaction.

Anyway my concern primarily is about the use of masks to control droplets, I think that's clear enough from my initial post.

And why cost shouldn't be a concern considering it seems to be ok to use much more costly interventions.

Its the contrary, if aerosols are the main part of the problem the mask are much less useful than considered, so the control of droplets falls to a secondary concern. Cost are exactly why it is important to determine exactly how important this mechanism is, because that is what determines how to spend the limited resources in the best possible way.

Our understanding so far is that airborne transmission is predominantly, though not exclusively, limited by proximity. That is why social distancing and masks are so important.

Yes, but if aerosols are as important as some people are trying to demonstrate, social distancing and mask as done right now would simply not be enough. For example right now it is considered you can safely ride an elevator if you take care of not contaminating your hand when pressing buttons, wear a mask, ride in small number of people and don't talk. But if aerosols are more important than what we think now that elevator would still be extremely dangerous and you should not ride one until it has been extensively ventilated after every use and you change your mask for a perfect-fit N95 respirator (those that actually make breathing quite more difficult). Many places would have no real safe way to function, from offices to supermarkets and hospitals.

1 ( +1 / -0 )

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