Despite recommendations that sexually active women 25 and younger be screened annually for chlamydia, less than half are tested that frequently, according to estimates from the Centers for Disease Control and Prevention.

Data from a national survey on chlamydia testing showed that just 38% of girls and young women ages 15 to 25 had been tested in the previous year.

The CDC estimates that there are 19 million new sexually transmitted infections in the U.S. each year - totaling $17 billion in healthcare costs - and chlamydia is the most commonly-reported infectious disease, with about 1.3 million cases reported in 2010. But, the agency estimates, the actual number is closer to 2.8 million because so many cases go unreported.

The new numbers, released Tuesday at the National STD Prevention Conference in Minneapolis, are cause for concern, according to the CDC, because untreated chlamydia can lead to chronic pelvic pain, potentially fatal ectopic pregnancy, and infertility.

Undiagnosed STDs lead to infertility in more than 24,000 American women each year, according to the CDC.

“This new research makes it clear that we are missing too many opportunities to protect young women from health consequences that can last a lifetime,” Kevin Fenton, MD, director of the CDC’s National Center for HIV/AIDS, Viral Hepatitis, STD and TB Prevention said in a press release.

“Annual chlamydia screening can protect young women’s reproductive health now and safeguard it for the future,” Fenton said.

The CDC also recommends that anyone diagnosed with chlamydia be retested three months after initial treatment in case of re-infection. Additional data presented at the conference showed that retesting rates are also low and many re-infections are likely missed.

Researchers examined data on 60,000 men and women who tested positive for chlamydia between 2007 and 2009 at healthcare facilities in New York, New Jersey, and the U.S. Virgin Islands and found that just 11% of men and 21% of women were retested for chlamydia within 30 to 180 days.

Of those who were retested, 25% of men and 16% of women tested positive again.

“It is critical that healthcare providers are not only aware of the importance of testing sexually active young women every year for chlamydia infections, but also of retesting anyone who is diagnosed,” wrote Gail Bolan, MD, director of CDC’s Division of STD Prevention in the press release.

“Chlamydia can be easily treated and cured with antibiotics, and retesting plays a vital role in preventing serious future health consequences,” Bolan said.

Bolan told MedPage Today that primary care doctors can play an important role in preventing the spread of chlamydia by asking young female patients about their sexual activity, and by routinely screening for chlamydia.

She said some clinics in areas that have successfully lowered chlamydia rates have trained registration clerks to offer a urine test or blood test to young women who come in to refill a birth control prescription and often to young women who come in for other reasons.

The CDC did find some good news: certain high-risk groups, including African American women, those who had multiple sex partners, and those who received public insurance or were uninsured, were the most likely groups to undergo chlamydia screening.

The researchers focused on testing rates in women because there’s no evidence that population-based screening for men is an effective strategy to reduce chlamydia, Bolan told MedPage Today. However, she noted, antibiotics are recommended for male sexual partners of women diagnosed with chlamydia.

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By Emily P. Walker, Washington Correspondent, MedPage Today