Chlamydia, a potentially dangerous sexually transmitted infection, is the most commonly reported infectious disease in the U.S., according to the CDC. But only 38 percent of sexually active women ages 15 to 25 report they’ve been tested for it during the past year.

That’s the bad news delivered Tuesday afternoon by the CDC in a press release about data presented today at the National STD Prevention Conference in Minneapolis.

Sexually active women under 25 are supposed to be screened annually for chlamydia, and those who test positive and administered antibiotics are supposed to be re-checked after 3 months to make sure the medicine has done its job. But the report found that re-testing rates were very low, too.

The good news is that testing rates are highest among populations who are at elevated risk of chlamydia infection: African-American women, those who had multiple sex partners, and those who received public insurance or were uninsured, according to the release.

Untreated, chlamydia can cause serious long-term health problems such as chronic pelvic pain, potentially fatal ectopic pregnancy and infertility, according to the CDC.