Here’s an Inconvenient Truth: Disease Is in the Air

Science writer Carl Zimmer’s latest book is a brilliant history of medicine that takes us from Louis Pasteur’s germ theory of the 19th century to present day. Along the way, it offers an anthropological study of medical culture — a culture capable of ignoring science when it wants to. That culture cost the lives of millions early in the pandemic, and here in British Columbia that culture remains strong. Zimmer’s book demonstrates that even when we understand the science of disease, governments often reject science on purely political grounds.

When Pasteur demonstrated the germ theory of disease in the late 19th century, it was a dramatic leap forward for medicine.

It was also a dramatic defeat for two competing theories of illness. One was the centuries-old belief that diseases arose in “miasmas,” or poisoned air that somehow infected and killed some people while leaving others unharmed. The other theory, promoted by Pasteur’s contemporary Rudolf Virchow, argued that poverty and ignorance (what we now call the social determinants of health) promoted disease.

Miasmas were consigned to history. Virchow’s social determinants were ignored because acting on them would require a social revolution.

The consequences of Pasteur’s triumph have reverberated since then, all the way to the hospitals and classrooms of British Columbia — not always in a good way.

Pasteur set off the hunt for disease-causing microbes that could be eliminated by clean water, drugs and vaccines.

Researchers looked for microbes in the air as well; Pasteur himself climbed a mountain to capture air above a glacier, and others demonstrated that tuberculosis could travel through the air impelled by a cough or sneeze. That led to the invention of the “mouth bandage,” a mask that could block bacteria.

But something in medical culture didn’t like the idea of airborne disease. It seemed too close to miasma theory.

In the early 1900s, a leading American doctor argued that medical masks were pointless because bacteria could survive only in droplets that would fall harmlessly to the ground. (Zimmer calls this the “soggy raisin” theory.)

A fringe science

Thereafter, airborne infection became a kind of fringe field. Plant biologists looked for, and found, evidence that plant diseases like wheat rust could travel hundreds of kilometres and still destroy wheat crops. Researchers used balloons and planes (sometimes piloted by Charles Lindbergh or Amelia Earhart) to capture bacteria and spores at high altitudes.

But “aerobiology” remained stubbornly fringe. The husband-and-wife team of William Firth Wells and Mildred Wells showed that tuberculosis could travel by air from a tuberculosis ward to a laboratory where it could infect guinea pigs, and also found evidence that ultraviolet lamps could help reduce the spread of measles in classrooms.

But the Wellses were known by their contemporaries as “difficult” people who didn’t get along with their colleagues or each other. William was a notoriously bad teacher, and no better as a writer: after years of work on a major book about airborne transmission, it needed massive editing — and still had no impact on medical science.

Even in the late 1930s, though, the U.S. military was thinking seriously about airborne transmission of dangerous microbes. When the U.S. entered the Second World War, the army recruited Theodor Rosebury, a professor of dentistry at Columbia University. Rosebury had studied oral bacteria and then moved on to more dangerous varieties.

Once in the army, Rosebury soon identified psittacosis (parrot fever) and anthrax as potential weapons of biological warfare. Both could be transmitted by air, and when Rosebury recovered from his own case of psittacosis he determined how he’d become infected: a leaky capsule had dripped onto the palm of his hand, and the resulting tiny splash had sent micro-droplets into the air. Some had risen high enough for him to inhale them.

During the war, Rosebury had tripled the lethality of anthrax. After the war, he tried to alert the public to the hazards of biowarfare, and got into serious political trouble for it.

Effectively blacklisted for his left-wing politics, Rosebury went back to research oral bacteria. And that led, in turn, to his discovery of the human microbiome — the trillions of bacteria, fungi and viruses that live in our bodies and help us function.

The U.S. government, meanwhile, was determined to be prepared for any potential biowar attack.

In one case, a U.S. naval submarine sprayed a harmless bacteria into the air above San Francisco Bay, and then found those bacteria in Bay Area residents.

Biowar attacks that never came

Postwar public health developed largely as a defensive measure against biowarfare. Alexander Langmuir, an old foe of the Wellses, became head of what eventually became the Centers for Disease Control and Prevention. Skeptical about airborne transmission, Langmuir made an exception for biological weapons, and devoted much of his time to building defences against silent biological attacks.

One positive result of his fears was the creation of the first epidemic intelligence service, which helped local authorities to identify and deal with disease outbreaks. Langmuir’s agents soon moved overseas as well. Zimmer tells us: “Some of the epidemiologists Langmuir trained would go on to help eradicate smallpox.”

But they never spotted any evidence of a Soviet biowarfare attack.

Zimmer moves through the rest of the book from outbreak to outbreak: the Hong Kong flu pandemic of 1957, H5N1 in Hong Kong in 1997 and all over the world since then; SARS-CoV-1 in 2003; H1N1 in 2009; Middle East Respiratory Syndrome in 2012.

Every outbreak brought more evidence of airborne transmission. A civil engineer found that a serious outbreak of H5N1 in a Hong Kong apartment building was aided by the building’s design: an air well carried both air and viruses from leaky plumbing on a lower floor into upstairs residents’ windows — and noses.

More religion than science

Still, public health authorities remained very reluctant to abandon the “soggy raisin” theory. David Milton, a researcher who learned to pull viral DNA out of the air, found few others interested in what he found. “The prevailing belief,” Zimmer writes, “was that respiratory infections didn’t spread by droplet nuclei; short-range droplets and fomites were largely responsible. ‘You grow up with this in medicine,’ Milton said. ‘It’s more religion than science, I would say.’”

And when SARS-CoV-2 erupted out of Wuhan early in 2020, no one wanted to think that it could be airborne. The economic and political consequences would have been intolerable.

True, the World Health Organization suggested early in the pandemic that the virus was airborne, but as Zimmer describes it, WHO Director-General Tedros Adhanom Ghebreyesus, known as Dr. Tedros, almost immediately walked that statement back:

“Sorry. I used the military word airborne. It means to spread via droplets or respiratory transmission” Dr. Tedros explained at a press conference that Zimmer describes in the book. “Please take it that way, not the military language.”

After this confusing explanation, Zimmer tells us, WHO went back to declaring COVID-19 was transmitted “via droplets and fomites during close, unprotected contact between an infector and infectee.”

If COVID-19 spread in droplets, then it was worthwhile to keep people two metres apart, to put up plexiglas barriers around checkout stands, and make supermarket aisles one-way. Sanitizing countertops could break the chain of infection.

But if COVID-19 was airborne, all those measures were pointless. The air in every workplace would be a soup of viruses; even outdoors, a single COVID-19 case in a big-enough crowd could spread infection in minutes. Masking, air purification and ultraviolet lamps could mitigate spread in confined spaces like classrooms and hospital wards, but could not eradicate the threat.

A tempest in a teapot?

Here in B.C., Dr. Bonnie Henry, our chief medical officer of health, stated in 2020 that the controversy over how COVID-19 was spread was a “tempest in a teapot.” In the first year of the pandemic, she maintained that SARS-CoV-2 spread via droplets. Not until December 2021 did she say that new COVID variants like Omicron could be airborne.

It’s now clear that official downplaying of COVID-19’s means of transmission helped to save the economy, but at a heavy cost. Supporters of public health, including health-care workers and medical scientists, lost their trust in health agencies. So did a large part of the public, who thought masks and then vaccines were attacks on their personal freedom.

Since then, a few people still mask and build Corsi-Rosenthal boxes to purify air in their homes or schools, but most of us, including politicians, prefer to think of the pandemic as over.

Carl Zimmer concludes his excellent book by showing how research has found microbes can go airborne with the crash of every wave on a beach, and from every wildfire. Microbes thrive in clouds, and form the nuclei of countless raindrops. We breathe them in and out, and most do us no harm at all.

But air pollution alone kills an estimated 8.1 million people yearly, before we even consider airborne infectious diseases like COVID-19, tuberculosis, measles and flu.

In the self-styled “advanced” nations, clean water is considered essential, but we tolerate foul air in our homes, workplaces and classrooms, despite a century of evidence that it is harming ourselves and our children.

And it isn’t likely we’ll purify the air we breathe until yet another airborne pandemic, perhaps H5N1 bird flu, kills yet more of us.