Mistakes

Quotation from Amused Bits

Speaking of mistakes… Somehow in May 2021 I missed the article by Megan Molteni in Wired titled The 60-Year-Old Scientific Screwup That Helped Covid Kill.

Note the date for that article. SARS-CoV-2 has continued to mutate since then, so a reassuring detail toward the end of the article is no longer true. If you read the article now, bear that in mind.

But the heart of the article is worth knowing about. The study of airborne particles has traditionally belonged to engineering and physics. When the medical community applied findings about this to airborne diseases, it chose the wrong threshold. As a result, public health has gotten it wrong about handling airborne diseases ever since.

In case you don’t have a subscription to Wired, here is the essence of what happened and why it especially matters now. If you do have a subscription, I highly recommend the article. It is a fine example of teamwork and persistence eventually penetrating the The Establishment’s determination not to consider anything that contradicts dogma. In this instance, the dogma is that airborne transmission of a pathogen only happens with particles 5 microns or less in size.

In 1934, William Firth Wells and his wife Mildred Weeks Wells (a physician) conducted experiments to analyze how gravity and evaporation affected respiratory particles. They plotted a curve of their findings. The curve showed how long it would take a particle of a specified size to fall from a person’s mouth to the ground. They found that particles bigger than 100 microns fell in a matter of seconds, while smaller particles floated longer.

The scientific sleuths who dug this up found William Wells’ 1955 book Airborne Contagion and Air Hygiene which is out of print.

The sleuths also noticed that in the 1940s William Wells put air-disinfecting ultraviolet lights in schools. Fewer children came down with measles in classrooms where he put UV lamps. This was decades before measles was acknowledged as a disease with airborne transmission.

Why weren’t these findings taken on board by public health authorities?

In large part because the chief epidemiologist of the newly established USA Centers for Disease Control, Alexander Langmuir, disparaged them. He thought they were a throwback to the outdated, discredited belief that diseases spread through “miasma.” He didn’t believe airborne transmission of disease could happen.

Langmuir did some useful thinking of his own, though. Looking at other studies done in the 1940s about particles in the air in mines and factories, he concluded that the nose and mouth are good at filtering out particles bigger than 5 microns. Particles smaller than that could get past this crucial defense.

William Wells noticed those studies too. He did experiments on rabbits and guinea pigs using tuberculosis, which causes lesions if it reaches the lungs but is unable to cause trouble if it doesn’t reach lung tissue. Wells’ experiments showed that TB on particles smaller than 5 microns could travel long distances through the air and cause infection, but TB on particles larger than 5 microns couldn’t. He published the last of his findings in 1962.

Langmuir was persuaded that TB transmission was airborne. Public health about how to limit its transmission had been wrong and needed to change. To clamp down on TB, airborne transmission on particles of 5 microns or less had to be addressed.

That’s when public health made the big mistake that caused most of the world to miss the boat about how to reduce transmission of the current pandemic. Public health used 5 microns as the dividing line between airborne transmission that can waft over significant distances and droplet transmission that falls to the ground after a few feet.

Public health based its dividing line on TB, an unusual pathogen that can only infect lung tissue and gets blocked from reaching its target unless it is on tiny particles able to get past our first line of defense at the nose and mouth. Most airborne diseases are not so choosy. The dividing line shown by experiments is actually 100 microns.

Why did this decades-old scientific mistake make our current pandemic worse?

Most public health authorities persistently advised governments and populations as though we are dealing with a virus that spreads mainly through fomites (particles we pick up from surfaces) or droplets (larger particles that fall down quickly after a short distance).

If that had been correct, social distancing and so on would have been enough to greatly reduce transmission, but it isn’t correct. We are dealing with an airborne pathogen and the definition of airborne has been wrong. It doesn’t need tiny particles. It can be airborne on particles 20 times the diameter we thought it needed. We can walk into an empty room a few hours after an infected person left it and still inhale infected airborne particles they left behind. We can be much farther than six feet from an infected person and inhale infectious particles from them.

SARS-CoV-2 in particular has no difficulty infecting a person when it is on a larger particle that gets caught in the nose. When that happens, it infects the olfactory system instead of the lungs. Altered or lost sense of smell is therefore a common symptom. Unfortunately the olfactory system leads directly to the brain, so the virus often goes there where studies show it causes damage.

Science is done by humans. We make mistakes. The way science works, eventually mistakes get recognized and corrected, but all sorts of consequences can happen during the interval before the correction occurs and becomes common knowledge.

Last but not least, I mentioned that the article in Wired contains a reassuring bit that is no longer true. Here it is:

“SARS-CoV-2, like many respiratory diseases, is airborne, but not wildly so. It isn’t like measles, which is so contagious it infects 90 percent of susceptible people exposed to someone with the virus. And the evidence hasn’t shown that the coronavirus often infects people over long distances. Or in well-ventilated spaces. The virus spreads most effectively in the immediate vicinity of a contagious person, which is to say that most of the time it looks an awful lot like a textbook droplet-based pathogen.”

Public health was too slow to recognize that this disease transmits as airborne, so we allowed the virus to spread like kudzu. The general public still doesn’t understand that it’s airborne, so we’re continuing in the same vein.

The virus has taken advantage. It mutates at a furious pace, like something out of a Grade B science fiction movie. Somewhere in the Omicron lineage, its variants became a rival to measles in terms of how contagious it is.

None of the reassuring portion from the 2021 story is true any more. The virus is now wildly contagious, can infect over significant distances and doesn’t require a target to be in the immediate vicinity of an infected person.

This doesn’t make us helpless. As with most mistakes, fixing it later takes more work than doing it right in the first place would have taken, but we can still do it. Wells showed in the 1940s some of what we can do.

We know what our mistake was. We know how to correct it. Lots of ventilation, lots of air filtration, lots of sterilizing UV (and we have far-UVC now which is easier to apply to occupied spaces than what Wells had to use)… and high quality face masks until we actually wrestle this pandemic down. The question is whether we are willing to admit we messed up and fix it.