According to
Emily Landon, medical director of antimicrobial stewardship and infection control at the University of Chicago Medicine, the hospital’s guidelines for influenza define exposure as being within six feet of an infected person for 10 minutes or longer.
“Time and distance matters,” Landon says.
Respiratory illnesses can also be spread through the surfaces upon which the droplets land—like airplane seats and tray tables. How long those droplets last depends both on the droplet and the surface—mucus or saliva, porous or non-porous, for example. Viruses can vary dramatically in how long they last on surfaces, from hours to months.
There’s also evidence that respiratory viruses can be transmitted through the air in tiny, dry particles known as aerosols. But, according to Arnold Monto, professor of epidemiology and global public health at the University of Michigan, it’s not the major mechanism of transmission.