Ex, it is a mortal sin for Catholics to miss Sunday Mass.
During Mass, hundreds, sometimes thousands of people, are crowded together in one large room. Parishioners dip their fingers in a bowl of holy water and bless themselves as they enter the church. During services they turn to people on their right and left, in front of them and behind them, and offer a handshake of friendship. If they partake of Communion, the priest and everyone else drinks from the same cup. The priest's fingers touch the Host, and he places it on your tongue, often touching your face and lips as he does so. He goes from person to person doing the same thing. As parishoners leave the church they shake hands with the Priest at the door.
Catholics only miss Sunday Mass if they are gravely ill. You may only receive Communion if you are free of sin - ie, have confessed and received absolution recently and not sinned in the meantime. During the Sacrament of Confession a line of people occupy a tiny closet one at a time, speaking to the priest through a mesh screen.
Those religious traditions create a petri dish. This is no secret. I questioned it as a very young child and I was told: GOD protects you - you will never, ever get sick from holy water, or standing next to someone who has the flu in Church.
When I was caring for my father and sister, who is so frail a bad cold could kill her, this was the subject of MANY arguments when a flu or cold bug was going around.
Practicing the Catholic religion during an epidemic WILL spread the disease. PERIOD. There's no way around that.