What to look for: Chlamydia is known as the "silent epidemic because as many as 85 percent of infected women and 40 percent of infected men with chlamydial infections report no symptoms, according to the CDC. If not adequately treated, 20 to 40 percent of women with chlamydia develop pelvic inflammatory disease (PID), which in turn causes problems such as infertility, ectopic pregnancy, and chron