Epidemiologists have long observed that most respiratory bacteria need close contact to spread. Yet in that small space, a lot can happen. A sick person may cough droplets on your face, emit small aerosols that you inhale, or shake your hand, which you then use to rub your nose. Any of these mechanisms could transmit the virus. “Technically, it’s very difficult to separate them and see what the cause of the infection is,” Marr says. For long-distance infections, only the smallest particles could be to blame. Up close, however, particles of all sizes were in play. Yet, for decades, droplets have been seen as the main culprit.
Marr decided to collect some data of his own. By installing air samples in places like day care and airplanes, he often found the flu virus where manuals say it shouldn’t be – hidden in the air, most often in particles small enough to stay in place. another hour. And it was enough to make people sick.
In 2011, it was supposed to be big news. However, major medical journals have rejected his manuscript. Even while he did new experiments that added evidence to the idea that the flu infected people via aerosols, only a niche editor, In Journal of the Royal Society Interface, was consistent in his work. In the silent world of academia, aerosol had always been the domain of engineers and physicists, and pathogens were purely a medical concern; Marr was one of the few people who tried to ride in the division. “I was definitely a fringe,” she says.
Thinking it might help overcome this resistance, I would occasionally try to figure out where the 5 micron defective figure was coming from. But it has always been blocked. Medicine manuals are simply stated as facts, without a quote, as if they were pulled from the air itself. In the end she gets tired of trying, her search and her life are over, and the 5 micron mystery vanishes deep. Until, that is, December 2019, when a newspaper ran through his desk from Yuguo Li’s lab.
Researchers inside the University of Hong Kong, Li had made a name for himself during the first outbreak of SARS, in 2003. His investigation into a fire in the Amoy Gardens apartment complex provided the strongest evidence that a coronavirus could be in the air. But in the intervening decades, he had also struggled to convince the public health community that his risk calculation was disabled. Finally, he decided to work on the math. Li’s elegant simulations showed that when a person coughed or sneezed, heavy droplets were too few and the targets – an open mouth, nostrils, eyes – were too small to explain many infections. Li’s team had concluded, therefore, that the public health facility had pushed him back and that most colds, flu and other respiratory illnesses should spread through the aerosol.
Their findings, they argued, exposed the fallacy of the 5 micron boundary. And they had taken it a step further, tracing the number in a decade-long document the CDC had released for hospitals. Marr couldn’t help but feel a source of excitement. A reporter had asked her to review Li’s diary, and she did not mask her feelings while writing her response. On 22 January 2020, he wrote: “This work is very important to challenge the existing dogma on how infectious disease is transmitted in droplets and aerosols.”
Even as she composed her note, the implications of Li’s work were far from theoretical. Hours later, Chinese government officials cut off all travel outside the city of Wuhan, in a desperate attempt to contain a respiratory disease that has not yet been reported burning for the 11 million-strong megalopolis. When the pandemic closed country after country, the WHO and the CDC told people to wash their hands, wash surfaces, and maintain social distance. They didn’t say anything about masks or the dangers of being at home.