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Sexually transmitted infections (STIs) are common and an important cause of morbidity for sexually active young men. The Centers for Disease Control and Prevention (CDC) estimates that half of the 20 million new STIs that occur each year in the United States affect youth between the ages of 15 and 24 years.1 Globally, the burden of STIs is also high, with 357 million cases annually of syphilis, gonorrhea, chlamydia, and trichomoniasis alone.2 Aside from chlamydia and trichomoniasis, rates of most STIs are higher among men who have sex with men (MSM) than among men who have sex with women (MSW).

STIs are preventable. A clinical assessment of behavior and risk is essential to identify individuals in need of screening, evaluation, and treatment. Use open-ended questions, with nonjudgmental language. The five Ps strategy may be used to ascertain the 5 aspects of sexual history that are important in developing prevention and treatment strategies:

  • Partners (recent and past sex partners)

  • Practices (kind of sex performed, both recently and in the past)

  • Protection (protective measures used: e.g., condoms, preexposure prophylaxis [PrEP])

  • Past history of STIs (patient and partners)

  • Prevention of pregnancy (for MSW and women)

Here, we review the manifestations, diagnosis, treatment, and prevention of common infections solely or predominantly spread through sexual contact, including syphilis, gonorrhea, chlamydia, herpes simplex virus (HSV), and human papillomavirus (HPV). However, many other infections not classically considered STIs can be spread by sexual contact. Among these infections are gastrointestinal pathogens (e.g., Shigella, amebiasis), viral hepatitis (e.g., hepatitis A, B, and C), and methicillin-resistant Staphylococcus aureus. In addition, most of the 37 million people worldwide who are living with human immunodeficiency virus (HIV) acquired the infection sexually. The diagnosis, clinical presentations, and management of these infections are beyond the scope of this chapter.


Syphilis is a multisystem, potentially chronic infection caused by the spirochete Treponema pallidum. The number of syphilis diagnoses in the United States has risen substantially in recent years, and more than half of all new early-stage syphilis infections in the United States occur in MSM.3 In 2017, men accounted for almost 90% of early syphilis cases in the United States, and MSM accounted for 68.2%. Early syphilis rates among MSM have also continued to increase annually between 2000 and 2017. Syphilis is strongly linked to HIV acquisition. In a study of MSM at high risk for STIs, those with new syphilis infections had nearly 3 times the odds of subsequently acquiring HIV as those without syphilis.4 Infection with T. pallidum is spread by sexual contact with a partner who has early-stage syphilis.

Clinical Manifestations

Classically, syphilis progresses through 3 stages, though these stages are not discrete and may overlap. The cardinal feature of the first stage, also called ...

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