Sexually Transmitted Diseases (STDs)

Candida is a genus of dimorphic, opportunistic fungi. Candida albicans is part of the normal human flora and is the most common cause of candidiasis. Risk factors for infection include conditions or agents that may lead to an immunocompromised state, disruption of the normal flora, and/or disturbance of the mucosal barrier. The clinical presentation varies and can include localized mucocutaneous infections (e.g., oropharyngeal, esophageal, intertriginous, and vulvovaginal candidiasis) and invasive disease (e.g., candidemia, intraabdominal abscess, pericarditis, and meningitis). The diagnosis is made by identifying Candida on KOH preparation, cultures, or tissue biopsy. Treatment depends on the extent and site of infection, and includes topical or systemic antifungal medications

Neisseria is a genus of bacteria commonly present on mucosal surfaces. Several species exist, but only 2 are pathogenic to humans: N. gonorrhoeae and N. meningitidis. Neisseria species are non-motile, gram-negative diplococci most commonly isolated on modified Thayer-Martin (MTM) agar. These pathogens have many virulence factors, including fimbriae, lipooligosaccharide envelope proteins, a polysaccharide capsule (unique to N. meningitidis), and IgA protease. Gonococcal infections are sexually or perinatally transmitted and include gonorrhea, pelvic inflammatory disease, septic arthritis, and neonatal conjunctivitis. Meningococcal infections are transmitted via respiratory and oral secretions. They most commonly cause meningococcemia with petechial hemorrhages and meningitis.

Chlamydial infections are a group of infectious diseases caused by bacteria belonging to the Chlamydiaceae family. The 3 species that can infect humans are Chlamydia trachomatis, C. pneumoniae, and C. psittaci. The most common infection is an STI caused by C. trachomatis, which affects the genitourinary tract. Chlamydia is the most common sexually transmitted bacterial infection in the United States. Other species of Chlamydia mainly cause respiratory infections. Diagnosis is based on nucleic acid amplification tests. Management is with antibiotics. Untreated chlamydial infections may have serious consequences, including sterility, ectopic pregnancies, spontaneous abortions, and chronic pelvic inflammatory disease.

Chancroid is a highly transmissible STD caused by Haemophilus ducreyi. The disease presents with painful ulcer(s) on the genital tract (termed chancroid or “soft chancre”). Up to 50% of patients will develop painful inguinal lymphadenopathy. Furthermore, of that percentage, 25% may develop complications of the suppurative lymph nodes. Given the growth of H. ducreyi on a special medium (often not readily available), chancroid is diagnosed based upon clinical appearance and tests to rule out both syphilis and herpes (the most common causes of genital ulcers). Although the disease can resolve spontaneously, antibiotics (azithromycin or ceftriaxone) are the treatment of choice. Treatment should involve both patients and their sexual contacts.

Herpes simplex virus (HSV) is a double-stranded DNA virus belonging to the family Herpesviridae. Herpes simplex virus commonly causes recurrent infections involving the skin and mucosal surfaces, including the mouth, lips, eyes, and genitals. Typical mucocutaneous infections are characterized by an acute localized appearance of clusters of small, painful vesicles on an erythematous base. Although overlap exists, HSV-1 is classically associated with oropharyngeal lesions, whereas HSV-2 is mostly responsible for genital herpes, an STI. Systemic and severe infections including encephalitis, meningitis, and neonatal herpes may also occur. The diagnosis is made based on clinical presentation and history, which can be confirmed by the microscopic examination of a stained smear of a fresh vesicle, nucleic amplification test using PCR, direct immunofluorescence, or serologic tests. The therapy for mucocutaneous lesions is usually symptomatic, but antiviral therapies involving acyclovir, valacyclovir, or famciclovir are useful if given early, and are always part of the therapy for serious systemic infections.

Macrolides and ketolides are antibiotics that inhibit bacterial protein synthesis by binding to the 50S ribosomal subunit and blocking transpeptidation. These antibiotics have a broad spectrum of antimicrobial activity but are best known for their coverage of atypical microorganisms. Common macrolides are erythromycin, clarithromycin, and azithromycin. Side effects include GI upset, QT prolongation, and hepatotoxicity. Resistance mechanisms include ribosomal methylation or mutation, inactivation of the drug through enzyme production, or removal of the drug through efflux pumps.

The sulfonamides are a class of antimicrobial drugs inhibiting folic acid synthesize in pathogens. The prototypical drug in the class is sulfamethoxazole. Although not technically sulfonamides, trimethoprim, dapsone, and pyrimethamine are also important antimicrobial agents inhibiting folic acid synthesis. The agents are often combined with sulfonamides, resulting in a synergistic effect. The primary indication for use is treatment of urinary tract infection (although significant resistance has emerged). In addition, the drugs are used to treat and prevent opportunistic infections such as toxoplasmosis encephalitis and pneumocystis pneumonia in immunosuppressed individuals. The most common adverse events are hypersensitivity reactions, fever, rash, GI upset, and hematologic reactions. The drugs are generally contraindicated in pregnancy, young/ill infants, and individuals with megaloblastic anemia or severe renal impairment.

The vulva is the external genitalia of the female and includes the mons pubis, labia majora, labia minora, clitoris, vestibule, vestibular bulb, and greater vestibular glands. The vagina is the female genital canal, extending from the vulva externally to the cervix uteri internally. The structures have sexual, reproductive, and urinary functions and a rich blood supply, mainly arising from the internal iliac artery.

Haemophilus is a genus of Gram-negative coccobacilli, all of whose strains require at least 1 of 2 factors for growth (factor V [NAD] and factor X [heme]); therefore, it is most often isolated on chocolate agar, which can supply both factors. The most common pathogenic species is H. influenzae, which is transmitted through respiratory droplets and can cause epiglottitis, meningitis, otitis media, and pneumonia. H. ducreyi is transmitted through sexual contact and is the cause of chancroid, a type of genital ulcer.

Gonorrhea is a sexually transmitted infection (STI) caused by the gram-negative bacteria Neisseria gonorrhoeae (N. gonorrhoeae). Gonorrhea may be asymptomatic but commonly manifests as cervicitis or urethritis with less common presentations such as proctitis, conjunctivitis, or pharyngitis. Without antibiotic treatment, complications can occur. Complications for men may include epididymitis, prostatitis, balanitis, and periurethral abscess. Women may develop pelvic inflammatory disease, which can cause perihepatitis and fertility issues. Disseminated gonococcal infection is associated with fever, dermatitis, tenosynovitis, septic arthritis, and (rarely) endocarditis or meningitis. Gonorrhea diagnosis is made by microscopy, culture, or nucleic acid amplification tests. Management generally involves ceftriaxone, but treatment with doxycycline should be pursued if a coinfection with Chlamydia trachomatis (C. trachomatis) is not excluded.

Syphilis is a bacterial infection caused by the spirochete Treponema pallidum pallidum (T. p. pallidum), which is usually spread through sexual contact. Syphilis has 4 clinical stages: primary, secondary, latent, and tertiary. Primary syphilis begins with a chancre, a painless ulcer on the genitals. Progression to secondary syphilis manifests as a generalized maculopapular rash, which includes the palms and soles. The development of tertiary syphilis can cause severe neurologic (neurosyphilis), cardiovascular, and/or gummatous disease. The diagnosis is through both treponemal and nontreponemal testing. Penicillin G is the antibiotic of choice. The duration of management varies based on the stage of the disease.

Pelvic inflammatory disease (PID) is defined as a polymicrobial infection of the upper female reproductive system. The disease can affect the uterus, fallopian tubes, ovaries, and adjacent structures. Pelvic inflammatory disease is closely linked with sexually transmitted diseases, most commonly caused by Chlamydia trachomatis and Neisseria gonorrhoeae, as well as organisms associated with bacterial vaginosis, such as Gardnerella vaginalis. Common symptoms are lower abdominal pain, cervical discharge, and irregular vaginal bleeding. Complications of PID can include ectopic pregnancy, chronic pelvic pain, and infertility. Diagnosis is primarily clinical in addition to PCR testing of cervical specimens and sometimes imaging or laparoscopy. Due to its polymicrobial nature, PID treatment is with combination antibiotic regimens.

The term vulvovaginitis is used to describe an acute inflammation of the vulva and vagina. Vulvovaginitis can be caused by several infectious and non-infectious etiologies, and results from disruption of the normal vaginal environment. Common signs and symptoms include pain, pruritis, erythema, and edema of the affected region, as well as vaginal discharge and dyspareunia. The diagnosis is based on the clinical presentation, physical examination findings, and inspection of vaginal secretions. Management depends on the etiology, including antimicrobials for infectious causes.

Treponema is a gram-negative, microaerophilic spirochete. Owing to its very thin structure, it is not easily seen on Gram stain, but can be visualized using dark-field microscopy. This spirochete contains endoflagella, which allow for a characteristic corkscrew movement. The bacteria are able to avoid immune recognition and phagocytosis by forming a protective coating with fibronectin. Humans are the only reservoir and transmission is through human-to-human contact. The most common species involved in human disease is Treponema pallidum subspecies pallidum, which is the causative agent of syphilis. Other clinically relevant species include T. pallidum pertenue, T. pallidum endemicum, and T. carateum. These are the causative organisms for yaws, bejel, and pinta, respectively.

Chlamydiae are obligate intracellular gram-negative bacteria. They lack a peptidoglycan layer and are best visualized using Giemsa stain. Chlamydiae species have a complex replication cycle consisting of 2 morphological forms: elementary bodies and reticulate bodies. The family of Chlamydiaceae comprises 3 pathogens that can infect humans: Chlamydia trachomatis, Chlamydia psittaci, and Chlamydia pneumoniae. Sometimes, C. psittaci and C. pneumoniae are classified as a separate genus, Chlamydophila. C. trachomatis is the most common bacterium responsible for causing sexually transmitted diseases in the United States and is associated with urogenital infections, lymphogranuloma venereum, neonatal conjunctivitis, and trachoma. C. psittaci causes psittacosis (parrot fever), whereas C. pneumoniae causes atypical pneumonia.