The CDC reports that as many 1 in 20 teenage girls and women and more than 2 percent of the general population in America are infected with chlamydia. Why is this important?

Approximately 30 percent of women will go on and develop pelvic inflammatory disease if left untreated. PID is a risk factor for infertility.

Contrary to popular belief, those infected with chlamydia are often asymptommatic. That is why the USPSTF encourages screening young women for this disease with an A recommendation:

The U.S. Preventive Services Task Force (USPSTF) strongly recommends that clinicians routinely screen all sexually active women aged 25 years and younger, and other asymptomatic women at increased risk for infection, for chlamydial infection.

The USPSTF found good evidence that screening women at risk for chlamydial infection reduces the incidence of pelvic inflammatory disease and fair evidence that community-based screening reduces prevalence of chlamydial infection. The USPSTF concludes that the benefits of screening substantially outweigh the potential harms.

Screening can be done during a pelvic exam or using a urine sample. ("High rate of chlamydia found among U.S. teens", Reuters/MSNBC, Jul.13)