Chapter 52: Sexually Transmitted Infections

Sexually transmitted infections represent a major public health challenge in the United States, affecting millions annually across diverse demographics with particularly high incidence in adolescents and young adults. These infections are caused by viruses, bacteria, and parasites transmitted through sexual contact and exposure of mucous membranes to pathogenic organisms. Biological and behavioral factors significantly influence susceptibility, including the protective mechanisms of acidic vaginal pH and commensal lactobacillus flora in females, the prominence of the squamocolumnar junction in younger women, and mucosal microabrasions in males during sexual activity. Age, hormonal status, and previous infections substantially modify risk, while co-infections dramatically increase vulnerability to additional pathogens, particularly HIV. The most prevalent bacterial infections include chlamydia and gonorrhea, which frequently present asymptomatically yet can progress to serious complications such as pelvic inflammatory disease and epididymitis, while syphilis progresses through distinct clinical stages from primary chancre through secondary manifestations to potentially severe tertiary neurological and cardiac sequelae. Viral STIs including human papillomavirus, herpes simplex virus, and HIV present unique challenges due to their chronic nature and oncogenic potential in certain HPV strains. Parasitic infections such as trichomoniasis, though often asymptomatic, can cause characteristic clinical findings. Diagnosis relies on nucleic acid amplification testing as the gold standard for bacterial and parasitic organisms, while screening recommendations emphasize annual testing for sexually active young women and comprehensive site-specific screening for men who have sex with men. Management strategies encompass antimicrobial therapy for curable infections, antiviral suppression for chronic viral infections, partner notification and treatment within specified time windows, and mandatory reporting of notifiable diseases to public health authorities. Prevention encompasses primary strategies including vaccination and barrier protection, secondary prevention through regular screening and cervical cancer surveillance, and tertiary approaches emphasizing medication adherence and transmission prevention counseling.