The 60-Year-Old Scientific Screwup That Helped Covid Kill
“According to the medical canon, nearly all respiratory infections transmit through coughs or sneezes: Whenever a sick person hacks, bacteria and viruses spray out like bullets from a gun, quickly falling and sticking to any surface within a blast radius of 3 to 6 feet. If these droplets alight on a nose or mouth (or on a hand that then touches the face), they can cause an infection. Only a few diseases were thought to break this droplet rule. Measles and tuberculosis transmit a different way; they’re described as “airborne.” Those pathogens travel inside aerosols, microscopic particles that can stay suspended for hours and travel longer distances. They can spread when contagious people simply breathe.
The distinction between droplet and airborne transmission has enormous consequences. To combat droplets, a leading precaution is to wash hands frequently with soap and water. To fight infectious aerosols, the air itself is the enemy. In hospitals, that means expensive isolation wards and N95 masks for all medical staff.
….The books Marr flipped through drew the line between droplets and aerosols at 5 microns. A micron is a unit of measurement equal to one-millionth of a meter. By this definition, any infectious particle smaller than 5 microns in diameter is an aerosol; anything bigger is a droplet. The more she looked, the more she found that number. The WHO and the US Centers for Disease Control and Prevention also listed 5 microns as the fulcrum on which the droplet-aerosol dichotomy toggled.
There was just one literally tiny problem: “The physics of it is all wrong,” Marr says. That much seemed obvious to her from everything she knew about how things move through air. Reality is far messier, with particles much larger than 5 microns staying afloat and behaving like aerosols, depending on heat, humidity, and airspeed. “I’d see the wrong number over and over again, and I just found that disturbing,” she says. The error meant that the medical community had a distorted picture of how people might get sick.
Epidemiologists have long observed that most respiratory bugs require close contact to spread. Yet in that small space, a lot can happen. A sick person might cough droplets onto your face, emit small aerosols that you inhale, or shake your hand, which you then use to rub your nose. Any one of those mechanisms might transmit the virus. “Technically, it’s very hard to separate them and see which one is causing the infection,” Marr says. For long-distance infections, only the smallest particles could be to blame. Up close, though, particles of all sizes were in play. Yet, for decades, droplets were seen as the main culprit.”
The article then goes on to brilliantly capture the stubbornness of researchers in their pursuit of the truth. From Lindsey Marr, it pans to a graduate student brought in to help trace the history of the 5 micron rule as she was good at this particular form of forensics. “Randall had studied citation tracking, a type of scholastic detective work where the clues aren’t blood sprays and stray fibers but buried references to long-ago studies, reports, and other records.”
Almost a year after tweeting “FACT: #COVID19 is NOT airborne”, the WHO changed its stance, rather quietly:
“ON FRIDAY, APRIL 30, the WHO quietly updated a page on its website. In a section on how the coronavirus gets transmitted, the text now states that the virus can spread via aerosols as well as larger droplets. As Zeynep Tufekci noted in The New York Times, perhaps the biggest news of the pandemic passed with no news conference, no big declaration. If you weren’t paying attention, it was easy to miss.”