http://www.pitt.edu/~super1/lecture/lec13881/index.htm,

http://www.pitt.edu/~super1/lecture/lec13491/index.htm,

http://www.pitt.edu/~super1/lecture/lec13211/index.htm,

http://www.pitt.edu/~super1/lecture/lec2401/index.htm, and

http://www.pitt.edu/~super1/lecture/lec2411/001.htm on syphilis and STDs in the US.