COVID-19 is a zoonotic, which means that it can be passed from animal to humans. Although not confirmed, there is strong suspicion that a person contracted it at a “wet” market where perishable items are for sale like fresh meats, poultry, fish, and produce. Rapid spread between people happens in the form of respiratory droplets from sneezing, coughing, or speaking. These invisible droplets land in the air, on surfaces, or on another person. When droplets land on the other person’s mouth, nose or eyes, or they touch a surface where droplets have landed and then touch their face, that next person (or people) can easily catch COVID-19. That’s why spreading is enhanced by proximity — closeness — between people and why masks can protect transmission from one person to the next.
COVID-19 spreads rapidly from person to person because of the Ro number or R-naught. Ro reflects the number of people that one individual can infect through contact. If the Ro for a virus is less than 1.0 (as it was for MERS), spreading can stop on its own. The Ro for COVID-19 is thought to be between 2 and 3. Meaning, for each individual carrying COVID-19, s/he can infect 2 or 3 of their contacts. That’s why the virus spreads rapidly or, as many experts describe, exponentially: 1-> 2-> 4-> 8-> 16-> 32-> 64-> 128 and so on.