When antibiotic treatments were introduced in the late 1940s, the STD rates in the U.S. declined very dramatically. However, after the drastic cut of governmental prevention programs, the infection rates rose once more. By the early 1970s, they had risen to new heights. How easily STDs can spread, is illustrated by the diagram on the left, taken from a 1972 popular magazine. Shown here is the spread of syphilis in one American high school. Each figure represents at least one sexual contact. Some 40% of the students exposed did not become infected. How many of those treated preventively may have been infected is unknown. Please, note that syphilis is spread by both hetero- and homosexual contact. In the diagram, the total number of individuals is 63. Of these, 44 had only heterosexual contact, 16 had only homosexual contact, and 3 had both heterosexual and homosexual contact.