Can any of them come infected by the COVD-19?
The probability is very low. Almost all of the participants will come from areas where the presence of the COVD-19 is nil or extremely low.
By comparison, a number of passengers equivalent to three times the MWC go through the airports of Atlanta or Los Angeles, two times pass through the airports of London, Paris or Amsterdam each day, and 1.5 times through Madrid and Barcelona each day. And none of them closed so far.
The basic hygiene measures (handwashing, not sneezing or coughing to the open) and common sense are more solid and effective.
If we follow the same line of thinking (we shouldn't), we would have to close all the airports tomorrow.
edit: typo