Mary Horman (left), a registered nurse for Clackamas County, and Liz Baca, a disease intervention specialist for the county, search for the right address in an Oregon neighborhood. Part of their job is to get information to people who may have a serious, treatable infection, yet not realize it. Kristian Foden-Vencil/OPB hide caption
A tinted transmission electron micrograph of Chlamydia trachomatis bacteria (light purple/black) inside a cell. Chlamydia is the most common sexually transmitted disease in the U.S., with more than 1.7 million reported cases in 2017. Biomedical Imaging Unit, Southampton General Hospital/Science Source hide caption
A billboard above a gas station reads "Feel The Burn," a play on 2016 presidential candidate Bernie Sanders' campaign slogan, "Feel The Bern." It's actually promoting tests for sexually transmitted diseases. Nick Ut/AP hide caption
The bacterium that causes gonorrhea, Neisseria Gonorrhoeae, has become resistant to multiple kinds of antibiotics. BSIP/UIG via Getty Images hide caption
This is a color-enhanced transmission electron micrograph image of Neisseria gonorrhoeae, the bacterium that causes gonorrhea. David M. Phillips/Science Source hide caption
The bacteria that causes gonorrhea can cause infertility in women and men. BSIP/UIG via Getty Images hide caption
A microscope image, magnified 600 times, of the bacteria that cause the sexually transmitted disease gonorrhea. BSIP/UIG via Getty Images hide caption
A public health poster from 1952 encourages Americans to get checked for sexually transmitted diseases. Gonorrhea is the second-most-common sexually transmitted disease in the U.S., with more than 300,000 cases reported in 2011. Images from the History of Medicine hide caption
In the U.S., doctors no longer have the option of treating gonorrhea with a pill. Instead, they are advised to use an injectable antibiotic, which is still effective against the bacteria. iStockphoto.com hide caption
Health officials say they're worried that one day there will be no more antibiotics left to treat gonorrhea. iStockphoto.com hide caption