Many of the early identified patients in Wuhan, China had some link to a particular
seafood and live animal market, suggesting that is where the infection may have originated.
As the number of cases grew, however, patients reported no exposure to that market,
indicating that person-to-person spread was occurring.
As with other respiratory viruses, such as influenza for instance, this person-to-person
spread happens via respiratory droplets produced when an infected person sneezes or
coughs. The droplets can land in the noses and mouths of people nearby or be inhaled,
leading to infection. Many respiratory viruses also spread by fomite exposure (an
object carrying the infectious agent) when someone touches a surface with the virus
on it, then touches their mouth, nose or eyes without washing their hands. A recent
report from the Chinese CDC (China CDC Weekly, 2020, 2(8): 123-124) indicates a potential
fecal-oral route for spread as well. This may be an additional way COVID-19 is spreading
though more research is needed to confirm.
With most respiratory viruses, people are the most contagious when they have the most
symptoms, however, there are reports of spread to a close contact from someone showing
no symptoms.
Ultimately, this is a new disease and we are still learning exactly how it spreads
and the full extent of the illness it causes.