New research from the University of California, Davis and the Icahn School of Medicine at Mt. Sinai, provides evidence that the influenza virus can spread through airborne virus transport on microscopic particles called “aerosolized fomites.” The findings were published August 18, 2020, in Nature Communications.
“It’s really shocking to most virologists and epidemiologists that airborne dust, rather than expiratory droplets, can carry influenza virus capable of infecting animals,” said Professor William Ristenpart of the UC Davis Department of Chemical Engineering, who helped lead the research.
“The implicit assumption is always that airborne transmission occurs because of respiratory droplets emitted by coughing, sneezing or talking. Transmission via dust opens up whole new areas of investigation and has profound implications for how we interpret laboratory experiments as well as epidemiological investigations of outbreaks.”
The precise mode of transmission of the influenza virus has been a matter of debate for many years, however, there is broad agreement about the possible modes of transmission between humans. Obvious routes of transmission include droplets exhaled from the respiratory tract or on secondary objects such as door handles or used tissues.
These secondary objects are called fomites.So basically, what we have are direct and indirect routes of transmission, meaning the inhaling of virus droplets from an infected individual or direct transmission, and indirect transmission via fomites. But according to the researchers, little is known about which routes are the most important.
The researchers figured the answer may be different for different strains of influenza virus or for other respiratory viruses, including coronaviruses such as SARS-CoV-2. So using guinea pigs, the team used tiny, nonrespiratory particles they call “aerosolized fomites” to see if the fomites could carry influenza virus between guinea pigs.
Using an automated particle sizer to count airborne particles, they found that uninfected guinea pigs give off spikes of up to 1,000 particles per second as they move around the cage. Particles given off by the animals’ breathing were at a constant, much lower rate.
Immune guinea pigs with influenza virus painted on their fur could transmit the virus through the air to other, susceptible guinea pigs, showing that the virus did not have to come directly from the respiratory tract to be infectious.
The researchers also innoculated tissues with the influenza virus, let them get completely dry and then crumbled them up in front of the particle sizer. They were also able to infect cells from these particles released from the virus-contaminated paper tissues.
In conclusion the researchers wrote: “To our knowledge, no experimental evidence exists to establish that the airborne transmission of influenza viruses between experimental animals, or even between humans, occurs entirely via exhaled respiratory particles, as is commonly presumed. Our experimental data confirm that influenza virus transmission by aerosolized fomites is, at a minimum, biologically plausible.”
The study also noted that during the COVID-19 pandemic in China, air sampling in various hospital locations found the highest airborne genome counts of SARS-CoV-2 in rooms where health care workers doffed their personal protective equipment (PPE), hinting that virus was possibly being aerosolized from contaminated clothing as it was removed.
This is important information that requires further scientific consideration and rigorous investigation, especially in light of the COVID-19 pandemic.
