Whodunnit?

There is a story about an actress named Gene Tierney. Nope, this is not about a film featuring her. 

She performed one time in Hollywood Canteen and came down with German measles. Normally, rubella is not a serious illness except that Gene was pregnant. As a result, her child was born with certain deformities.

Years later, a fan came up to her and said that even though she was down with rubella, she chose to attend one of Gene's performance. At Hollywood Canteen. Poor Gene promptly fell into depression.

Normally, this would be an open and shut case except that it isn't. There was no proof that Gene contacted it from the fan. Nor could we even say that Gene's depression was due to the fan's admission.

This is the problem with contagious diseases. You can get it in the least expected ways. The infectious patient can take more care but it takes one moment of carelessness to spread it. 

It is even worse when the patient is not seriously ill. Then more people will want him or her to be working or active. 

The message is extremely relevant in the Covid19 outbreak. And no, I don't have an answer for this problem.