WASHINGTON (Reuters) -- Young women risk being infected with chlamydia more than once, researchers reported on Tuesday in a series of studies showing just how vulnerable younger women are to the disease.

But other studies presented at the Centers for Disease Control and Prevention conference showed that screening people can reduce the rate of infection across entire communities.

The findings may also show that younger women are more susceptible to and do not understand the risks of not only chlamydia, but other sexually transmitted diseases, the researchers told the conference being held in Jacksonville, Florida.

Chlamydia is the most common STD among women and, in 70 percent of cases, causes no symptoms. The bacterial infection can lead to pelvic inflammatory disease, ectopic pregnancy and infertility. It can also make a woman more likely to be infected with or to pass on the AIDS virus.

New York City Department of Health researchers Ellen Klingler and colleagues tested nearly 40,000 women in two studies, one in 2000 and another from 2003 to 2004.

One in eight women diagnosed with chlamydia citywide had a repeat infection within a year and a third of three happened within three months.

The women aged under 19 were much more likely to have been infected repeatedly than women over 25, they found.

A study of 400,000 women making routine doctor visits in California found similar rates, with one in 10 women infected with chlamydia becoming infected again within six months.

"These findings tell us that many young women who are treated for chlamydia are likely being reinfected by husbands who are not being diagnosed and treated," said Dr. Ronald Valdiserri, director of the National Center for HIV, Sexually Transmitted Diseases and Tuberculosis Prevention.