Children caught measles after entering a consulting room that an infected child had already left. Which property of droplet nuclei explains this?

1. Droplet nuclei are the dried residue of droplets and measure less than five microns. 2. Unlike droplets, which fall to the ground within a few feet, nuclei remain suspended in the air for long periods. 3. Measles virus therefore lingered in the room after the infected child left, and infected the next children to enter. 4. If nuclei fell quickly, the room would be safe once the infected child had gone, so the first option would rule out the event described. 5. Growth inside a vehicle happens with agents such as botulinum toxin in canned food, not with airborne particles. 6. Airborne transmission needs no vector, which is exactly why an empty room stayed infectious. _Source: CDC Principles of Epidemiology in Public Health Practice, 3rd Edition, section Modes of Transmission_