Chlamydia

Chlamydia is the most commonly reported bacterial sexually transmitted infection worldwide, caused by the bacterium Chlamydia trachomatis. Approximately 4 million new cases occur annually in the United States, with nearly two-thirds affecting young people aged 15–24. It spreads through vaginal, anal, or oral sex without condoms.

Most infected individuals—especially women—have no symptoms, making it a "silent" infection. When symptoms appear 1 week to months later, women may experience abnormal vaginal discharge, bleeding after sex or between periods, burning during urination, and lower abdominal pain. Men may notice white, cloudy, or watery penile discharge, burning or itching around the penis and testicles, and testicular pain or swelling. Rectal infection causes pain, bleeding, and discharge; throat infection may cause sore throat.

Untreated chlamydia leads to severe complications: pelvic inflammatory disease (PID), infertility, ectopic pregnancy, and chronic pelvic pain in women. Men can develop epididymitis and infertility. It increases HIV transmission risk and can cause premature delivery or newborn eye/lung infections during childbirth.

Diagnosis uses urine tests or swabs. Treatment involves antibiotics—single dose or 7 days. Partners must be treated, and sex should be avoided for 7 days. Annual screening is recommended for sexually active women under 25. Condom use prevents infection.