April 16 (HealthDay News) -- A nationwide assessment of screening data finds that while rates of testing for sexually transmitted chlamydia have risen since 2000, more than 50 percent of young, sexually active U.S. women still do not get screened.

Researchers at the U.S. Centers for Disease Control and Prevention combed through 2000-07 data reported by commercial and Medicaid health plans to the Healthcare Effectiveness Data and Information Set.

They found that chlamydia screening has charted a general rise -- from 25.3 percent of sexually active women aged 16 to 25 in 2000, to 43.6 percent in 2006. Data from 2007 showed a slight decrease in screening, to 41.6 percent.

While screening rates rose in all regions of the country, testing was most common in the Northeast (45.5 percent) and least common in the South (37.3 percent), the CDC reported. Hawaii reported the highest rate of chlamydia screening (57.8 percent), while Utah reported the lowest (20.8 percent).

In 2007, an estimated 1.1 million cases of chlamydia were reported to the CDC, and more than half of those cases involved females aged 15 to 25 years old, the report said.

The findings were published in the April 17 issue of the CDC's Morbidity and Mortality Weekly Report.

According to the CDC, Chlamydia trachomatis infection remains the most common bacterial infection transmitted via sexual contact in the United States, with an estimated 2.8 million cases reported annually. Chlamydia infection typically has no symptoms, but if untreated can lead to pelvic inflammatory disease, chronic pelvic pain, ectopic pregnancy and infertility.

The CDC noted that the data only included young women who were covered by some form of health insurance, but "18.4 percent of females aged 16-20 and 28.2 percent aged 21-25 were uninsured in 2007." These women are even less likely than insured women to be able to access STD screening, the agency said.

SOURCE: April 17, 2009, Morbidity and Mortality Weekly Report, U.S. Centers for Disease Control and Prevention, Atlanta