How come I have pneumonia, but nobody else in the family has it?

Pneumonia. There are relatively few causes of pneumonia which are readily transmitted person to person. Atypical pneumonia due to mycoplasma may occur in families but the illnesses are often weeks apart because of the slow transmission rate of this bug.
Huh? It's an infection. Everyone around you doesn't have to get the same infection. If someone gets a cold or a skin infection, do you always get it too?