They call it a hidden epidemic because most people who carry the disease don't show symptoms.

But chlamydia, the most common communicable disease in Stanislaus County, will no longer be a secret syndrome if the Health Services Agency has its way.

County health officials will soon launch a prevention and awareness program, aimed at sexually active women who are most at risk. A $16,000 grant from the state will pay for brochures that will be distributed at presentations, clinics and health fairs.

Dr. Don Zweig, an emergency specialist at the county's Urgent Care Center in Modesto, said chlamydia is most often found in young women who have sex with multiple partners and do not use condoms. "It's mainly a problem for women," Zweig said. "And it's one of the leading causes of infertility."

Symptoms include painful urination or unusual vaginal bleeding in women, and inflammation of the testicles in men. If left untreated, chlamydia can cause infertility in women, or complications during pregnancy. Chlamydia is on the rise across the state, but has dropped somewhat in Stanislaus County, according to the Health Services Agency.

The county reported 953 cases in 1998, 80 percent of them in women. That's down from 1,058 cases in 1991, according to the agency's statistics.

Despite the decline, the county's rate of infection -- about 220 cases per 100,000 residents -- is not far below the statewide average, which is about 235 cases per 100,000 residents.

Jean Yokotobi, the county's HIV/STD coordinator, said the disease is still a critical public health concern.

"It's gone down a little bit, but not significantly," she said.

The grant program, which recently doled out money to all counties, was started by the California Department of Health Services, the California Health Care Foundation and the University of California at San Francisco to reduce chlamydia by 50 percent by 2004.

Elaine Batchlor, vice president of the Oakland-based California Health Care Foundation, said the group effort was prompted by rising infection rates and the belief that many cases go undetected.

"It's been around for a long time," Batchlor said of the disease. "It's just reached epidemic proportions."

The good news is that chlamydia can be cured with antibiotics, if detected early.

Screening consists of a vaginal swab or a urinalysis.

Phyllis Franklin, a spokeswoman for Planned Parenthood offices in Modesto, Manteca, Stockton and Tracy, said such testing is on the rise.

"We're offering it more often to women who come in for other things," she said.

Zweig reminded that prevention is easy.

"The best way to prevent it is to use condoms," he said. "But it's amazingly difficult to get people to do that."