Sentinel surveillance of rectal chlamydia and gonorrhea among males--San Francisco, 2005-2008.

Rectal gonorrhea cases among males remained stable in San Francisco during 2005-2008, but rectal chlamydia increased 38 percent. While testing increased, rectal gonorrhea positivity declined at the STD clinic, and both infections remained stable elsewhere. Sentinel surveillance provides a better understanding of disease trends than case reporting alone.