Anyone in contact with a secretion (such as phlegm) from the respiratory passages of an infected person risks contracting the mycoplasma organism. However, close contact is required for transmission, so the virus is more commonly found among members of the same family and in schools and day-care institutions. There is little point in isolating someone infected with the virus since some people carry the infection without feeling ill.

Mycoplasma infections are most common in the 5 to 20 age range, though the disease is usually more dangerous among the middle-aged and elderly. An epidemic occurs every three to five years.