Bacterial STIs include chlamydia, gonorrhea, and syphilis.
Chlamydia is the most common STI in the United States and is most common among teens and young adults. For more information on chlamydia, visit the CDC's chlamydia page, and this Chlamydia Fact Sheet (pdf).
Anyone who is sexually active is susceptible to gonorrhea. Gonorrhea is especially common among young people between the ages of 15 and 24. For more information on chlamydia, visit the CDC's gonorrhea page, and this Gonorrhea Fact Sheet (pdf)
Syphilis infection is divided into four distinct stages: primary, secondary, latent, and tertiary, and there are different signs and symptoms with each stage of illness. For more information, refer to the Syphilis Fact Sheet (pdf) and visits the CDC's syphilis page