Sex Parasite Is Most Common in Women Older Than 40, Study Finds

A sex disease that’s more prevalent than gonorrhea and chlamydia, and less well-known, is suffered by 13 percent of women aged 50 and older, a study found.

The sexually transmitted parasite Trichomonas vaginalis causes urogenital infection, and can raise susceptibility to HIV. A study, reported at the International Society for STD Research in Quebec City, found the infection is twice as prevalent in those over 40 than in younger women because it isn’t adequately screened for. Women in their 40s had an 11 percent infection rate, according to the data.

Most STDs are more common in young people, said the study’s senior author, Charlotte Gaydos, a professor at Johns Hopkins University School of Medicine. Instances of syphilis, gonorrhea and chlamydia must be reported by doctors to state and federal health officials. There’s no mandate to do that for Trichomonas even though an estimated 7.4 million new cases occur every year.

“It’s not a reportable disease, although it’s more prevalent than chlamydia and gonorrhea combined,” Gaydos said in a telephone interview. “Maybe we should make this reportable and get good data.”

The study, of 7,593 U.S. women aged 18 to 89 in 28 states, showed an 8.3 percent overall infection rate among women. Testing is needed because most infected people show no symptoms, according to the study.

In men, the parasite is usually asymptomatic, according the U.S. Centers for Disease Control and Prevention in Atlanta. In women, infection can also cause pelvic inflammatory disease, vaginal discharge and low birth weight babies.

Single-Cell Protozoan

For a long time it was difficult to test for Trichomonas, because doctors had to grow the parasite in culture or see it in a sample. The organism, a single-cell protozoan, doesn’t survive well outside the body, so those tests were inaccurate about half the time, Gaydos said.

Gen-Probe Inc. (GPRO) of San Diego manufactures a test for the disease now, she said. She was involved in the clinical trials for the test’s regulatory approval. The test was approved April 20 by the U.S. Food and Drug Administration.

Gen-Probe provided tests but did not fund the study, Gaydos said.

To contact the reporter on this story: Elizabeth Lopatto in New York at

To contact the editor responsible for this story: Reg Gale at

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