A 30-year-old male presents with small, painless ulcers on his penis. He reports that they appeared about three weeks after he had unprotected sex. What might be the cause, and what are the next steps?
The painless ulcers this patient is describing are suggestive of primary syphilis, caused by the bacterium Treponema pallidum. However, other STIs such as herpes could present similarly, although herpes sores are typically painful. A dark-field microscopy examination of a sample from the ulcer could confirm the diagnosis of syphilis. If positive, he should be treated with penicillin, and his sexual partners should be informed, tested, and treated if necessary.