ST. LOUIS • The jukebox blared and disco balls flashed at the public health clinic Wednesday night inside Rehab lounge on Chouteau Avenue.

Once or twice a week, educators and disease investigators from the St. Louis city health department and community groups head to bars, restaurants and social events to talk about sexually transmitted diseases, pass out condoms and offer free testing.

New cases of chlamydia, gonorrhea and syphilis increased in 2010 in St. Louis, especially among young adults, according to an annual report released Thursday by the U.S. Centers for Disease Control and Prevention.

The city ranks second, third and 20th for its rates of the three diseases, respectively, among independent cities and counties nationally. The most common infection - chlamydia - was diagnosed in more than 4,500 residents in 2010, an increase of about 125 from the year before.

Since more than two-thirds of the new STDs are diagnosed in people younger than 30, public health workers increasingly go to their hangouts and use social media networks to reach them. Last year, the city helped offer more than 6,000 STD tests in nontraditional settings.

Health workers target happy hours and weekend nights in different areas of the city - gay bars in the Grove neighborhood, Latino dance clubs and other hot spots on Washington Avenue. One worker wore tight jeans, a leather jacket and a Cardinals hat, blending in with the crowd as he passed out condoms attached to bead necklaces. The workers start conversations about safe sex and offer free HIV swabs and syphilis blood tests.

"When we're out here we put a regular face on public health, we're not walking around in white lab coats," said Kevin Sanders, a disease investigator for the city's health department.

The casual approach helps reduce the stigma and embarrassment of going to a doctor's office or clinic, the public health workers said. One drawback of the mobile outreach is the workers don't always have access to a bathroom for gonorrhea and chlamydia urine tests.

Kea Thompson of St. Louis said she'd been meaning to get tested for HIV but hadn't gotten around to it before she spotted the health workers in Rehab. They gave her a cheek swab test that takes three minutes to complete. The results come back in about a week, and the person is notified.

"Everybody thinks it's a shame thing," said Thompson, 28. "I'd rather do it out in the open instead of being afraid and not getting tested."

The street team walked along the sidewalks of Manchester Avenue, stopping to visit the traditionally gay bars along the way. At some bigger events such as the annual PrideFest, they test hundreds of people. During the happy hour outings they might reach a few dozen.

"We know when people go out they don't want to hear about HIV," said Rochelle Turner, a program manager for the health department. "We try to do it in a way that's not threatening."

For syphilis, health workers have focused on reaching gay men, who make up the majority of new cases. Health officials attribute that in part to anecdotal knowledge that some HIV-positive men who have sex with other HIV-positive men feel like they can forgo condoms.

Bartenders said they welcomed the opportunity to provide free health services to their customers.

"It's a bad topic but it's something that has to be talked about," said Rob George, who poured drinks Wednesday at Rehab. "It doesn't affect the mood of the crowd."

Sexually transmitted diseases disproportionately affect African-Americans, who account for more than nine out of 10 of the city's reported chlamydia and gonorrhea cases. Public health officials say the disparity is partly explained by a lack of access to health care. They also think the targeted testing and education has helped identify more disease.

The city health department provides STD education to every high school in the city, the juvenile detention center and boys and girls clubs.

For the last year, health providers in Missouri have also had another tool to fight STDs. Expedited partner therapy, passed by the Legislature in 2010, allows doctors to dispense multiple dosages of antibiotics to patients testing positive for chlamydia or gonorrhea so they can pass the medicine along to their sexual partners. The diseases can lead to infertility if untreated.

Disease investigators in St. Louis County have increasingly turned to social media to track down the sexual partners who may be at risk.

When they interview a person who has been diagnosed with an STD, health workers armed with tablet computers ask for help identifying partners on Facebook or Twitter. The workers send private messages to the partners, alerting them that they may have been exposed to an STD and they should contact the health department for testing and treatment.

"The challenge for us as public health and health care providers is to craft those messages to suit the population subcultures that we're dealing with," said Dr. Faisal Khan, director of communicable disease control for the St. Louis County health department. "It's very hard for government agencies to plug themselves into those networks."