The Streptococcus bacteria that causes strep throat can be found on the skin and in the throat of people all over the world. The presence of the bacteria sometimes causes no infection at all, but if an individual’s immune system is weakened and the bacteria is not kept in check, infections can occur.
The Streptococcus bacteria is spread by person to person contact with either an infected wound or discharge from an infected nose or throat. The bacteria can be passed person to person if no infection is present but it is much less likely to cause an infection. In other words, infections of Streptococcus bacteria create more contagious situations.
According the eNotes Reference page on Streptococcal Infection (referenced below) Streptococcus bacteria is not only responsible for causing strep throat, but also puerperal sepsis, Streptococcal tonsillitis, rheumatic fever, and scarlet fever; all of which has caused severe public health risks in the past.