Nearly one in two African American adults has genital herpes. Could it be you? Could it be your partner? . . . A simple blood test is the best way to know if you have it. That's the language of an advertisement that has begun running in publications and on radio stations with largely black audiences in cities including Baltimore, Detroit and Atlanta. The ad is part of a campaign by drugmaker GlaxoSmithKline to educate blacks about genital herpes, a sexually transmitted disease that is far more common among African Americans than other racial or ethnic groups. The effort has divided public health authorities and raised complicated questions about race, sex, disease and commerce. As a pharmaceutical marketing tool, it may set a new standard for candor -- and controversy.