Chicago ? At least one in four teenage American girls has a sexually transmitted disease, suggests a first-of-its-kind federal study that startled some adolescent-health experts.

Some doctors said the numbers might be a reflection of both abstinence-only sex education and teens’ own sense of invulnerability. Because some infections can cause infertility and cancer, U.S. health officials called for better screening, vaccination and prevention.

The overall STD rate among the 838 girls in the study was 26 percent, which translates to more than 3 million girls nationwide, researchers with the U.S. Centers for Disease Control and Prevention found. They released the results Tuesday at an STD prevention conference in Chicago.

The teens were tested for four infections: human papillomavirus, which can cause cervical cancer and affected 18 percent of girls; chlamydia, 4 percent; trichomoniasis, 2.5 percent; and genital herpes, 2 percent.

Disease rates were significantly higher among black girls. Nearly half had at least one STD, versus 20 percent among both whites and Mexican-Americans.