Shelby is a 28-year-old cisgender man who presents to your primary care clinic to establish care. He recently completed a rehabilitation program for substance use. His social history is notable for prior injection drug use and previously trading sex for shelter. He is currently sexually active with both men and women. He reports oral, insertive anal, insertive vaginal, and receptive anal sex. He reports using condoms consistently with all sexual activities. He completed recent HIV and viral hepatitis screening at his rehabilitation program, which showed no evidence of hepatitis B, hepatitis C, or HIV infection. He feels well with no symptoms. His physical exam is normal. In addition to syphilis testing, what additional tests do you recommend?