STI Test: what are common causes?

Common causes of sexually transmitted infections (STIs) include bacteria (e.g., Chlamydia trachomatis, Neisseria gonorrhoeae, Treponema pallidum), viruses (e.g., HIV, herpes simplex virus, human papillomavirus, hepatitis B), and parasites (e.g., Trichomonas vaginalis). Transmission typically occurs through unprotected vaginal, anal, or oral sex. Many STIs are asymptomatic initially, which facilitates further spread. An STI test (e.g., urine, swab, or blood test) can detect specific pathogens. The provided context does not contain information about STI tests or their causes; this answer is based on established medical knowledge. Note: If an STI is suspected, a physician should always be consulted, as self-testing without clinical interpretation carries risks.