TUESDAY, July 12 (HealthDay News) -- The sexually transmitted disease trichomoniasis may be much more common among older women than those in their 20s, and researchers are recommending routine screening for sexually active women aged 40 and older.

"We usually think of STDs as more prevalent in young people, but our study results clearly show that with [trichomoniasis], while too many young people have it, even more, older women are infected," said the study's senior study investigator, Charlotte Gaydos, professor at the Johns Hopkins University School of Medicine, in a university news release.

Trichomoniasis (commonly known as "trich") is caused by the parasite Trichomonas vaginalis. It is the most common sexually transmitted disease in the United States, according to the Centers for Disease Control and Prevention (CDC). The World Health Organization estimates that 173 million people worldwide become infected every year.

The study, slated for presentation Tuesday at the annual meeting of the International Society for STD Research in Quebec City, Canada, also revealed that black women were more than three times as likely to be infected as whites (20 percent vs. 5.7 percent). The study authors speculated that differences in income, education and employment could explain this disparity.

The infection is easily cleared up with antibiotics. If left untreated, however, trichomoniasis can lead to severe health problems, such as pelvic inflammatory disease or complications during pregnancy, such as premature labor.

In studying 7,593 U.S. women 18 to 89 years old across 28 states, the researchers found that 8.7 percent tested positive for trichomoniasis, but the STD was more prevalent among older women. Thirteen percent of women 50 and older had the parasite, and women in their 40s trailed closely behind with an 11 percent infection rate, the study found.

Women in their 20s, on the other hand, had an infection rate of 8.3 percent.

"Trichomonas infections are quite treatable with antibiotics," said Gaydos. "And these high numbers really warrant older women getting screened by their family physicians and gynecologists during routine check-ups to make sure they are not infected and are not inadvertently spreading it to others."

Infected people may not experience symptoms, which typically include liquid discharge from the vagina or penis, irritation while urinating and genital itching.

"What we are really witnessing with trichomonas, especially in older women, is that no one ever looked, no one ever tested and diagnosed, and no one is really getting treated, so the infection persists year after year," said Gaydos. The study authors added that federal agencies should require that trichomoniasis be reported to the CDC like other STDs, such as chlamydia and gonorrhea, so that public health officials can better track and prevent the condition.

Men should also be tested and treated for trichomoniasis to reduce the risk of re-infection, particularly in situations involving multiple sex partners, the authors said.

Experts note that research presented at meetings is considered preliminary because it has not been subjected to the rigorous scrutiny required for publication in a peer-reviewed medical journal.

More information

The U.S. Centers for Disease Control and Prevention provides more information on trichomoniasis vaginalis.