The "South" has the highest concentration per 100,00 of chlamydia, gonorrhea, and syphilis while its AIDS rate is just shy the Northeast. The "South" though includes Maryland and the District of Columbia. While this different cultural appendage compared to the South does add to the South's numbers, it is undeniable that sexual diseases have found elements of poorer Southern culture, in a sense long in rebellion against mainstream southern Christian cultural norms, rich territory to infect.
The Midwest has the second highest rates of Chlamydia and gonorrhea. However, its syphilis and especially AIDS rate are the lowest in the country. The split between the two groups of diseases is who gets them. Chlamydia is the widest spread STD in the United States. Gonorrhea is the second most common STD but only at a forth of chlamydia's level. The other two diseases, syphilis and AIDS, are much less widespread though deadlier. These two diseases are primarily homosexual diseases with 72% of syphilis cases being from male-male sex while the Center for Disease Control says 63% of new AIDS cases are homosexual males. Either the Midwest's homosexual population has healthier sexual culture or the Midwest simply has less homosexuals compared to the rest of the United States. Which explanation is true I do not know.
The full chart with more information is available by clicking or downloading the image below.