Sexually Transmitted Infections: Overview and Clinical Approach¶
Chapter 141 | Part 5: Infectious Diseases
KEY CLINICAL POINTS¶
- STIs are among the most common infectious diseases globally, with over 357 million new cases annually of curable STIs (gonorrhea, chlamydia, syphilis, trichomoniasis).
- Sexual transmission is a critical mode for pathogens like Neisseria gonorrhoeae, Chlamydia trachomatis, and HIV, with emerging evidence for other viruses (e.g., Zika, Ebola).
- STIs contribute to significant morbidity, including infertility, HIV transmission risk, and malignancies (e.g., cervical cancer from HPV).
- Screening and prevention are vital, with HPV vaccination reducing cervical cancer incidence and male circumcision lowering HIV risk.
- Early diagnosis and partner management are essential to prevent complications and reduce transmission.
1. DEFINITION & OVERVIEW¶
Sexually transmitted infections (STIs) are infections acquired through sexual contact. They are a major global health burden, with over 357 million new cases annually of curable STIs. STIs can lead to severe complications, including infertility, HIV transmission, and malignancies. Sexual transmission is a primary mode for pathogens like Neisseria gonorrhoeae, Chlamydia trachomatis, and HIV, with emerging evidence for other viruses (e.g., Zika, Ebola).
Table 141-1: Sexually Transmitted and Sexually Transmissible Microorganisms¶
| BACTERIA | VIRUSES | OTHERa |
|---|---|---|
| Neisseria gonorrhoeae | HIV (types 1 and 2) | Trichomonas vaginalis |
| Chlamydia trachomatis | Human T-cell lymphotropic virus type 1 | Pthirus pubis |
| Treponema pallidum | Herpes simplex virus type 2 | Sexual Transmission Repeatedly Described but Not Well Defined or Not the Predominant Mode |
| Haemophilus ducreyi | Human papillomavirus (multiple genital genotypes) | |
| Klebsiella (Calymmatobacterium granulomatis) | Hepatitis B virusb | |
| Ureaplasma urealyticum | Molluscum contagiosum virus | |
| Mycoplasma genitalium | Cytomegalovirus | |
| Gardnerella vaginalis | Epstein-Barr virus |
| BACTERIA | VIRUSES | OTHERa |
|---|---|---|
| Helicobacter cinaedi | Hepatitis D virus | |
| Helicobacter fennelliae | Zika virus | |
| Anaerobes associated with bacterial vaginosis (?) | Ebola virus | |
| Epstein-Barr virus | ||
| Hepatitis A virus | ||
| Giardia lamblia | ||
| Entamoeba histolytica |
1.1 Global Impact¶
STIs are among the most common infectious diseases worldwide. In developing countries, STIs account for 90% of global cases. STIs contribute to significant morbidity, including infertility, HIV transmission, and malignancies (e.g., cervical cancer from HPV).
1.2 Transmission Modes¶
Sexual transmission is the primary mode for many STIs. However, some pathogens (e.g., Shigella, Hepatitis A) can also spread via oral-fecal routes. The role of sexual transmission in certain viruses (e.g., Ebola, Zika) is increasingly recognized.
2. EPIDEMIOLOGY¶
STIs are prevalent globally, with over 1 million new cases daily. In developing countries, STIs account for 90% of global cases. Risk factors include population growth, rural-to-urban migration, limited reproductive health services, and poverty. In the U.S., the CDC reports annual incidence rates for gonorrhea, chlamydia, and syphilis, with disparities among demographics.
Table 141-2: Major Sexually Transmitted Disease Syndromes and Sexually Transmitted Microbial Etiologies¶
| SYNDROME | SEXUALLY TRANSMITTED MICROBIAL ETIOLOGIES |
|---|---|
| AIDS | HIV types 1 and 2 |
| Urethritis: males | Neisseria gonorrhoeae, Chlamydia trachomatis, Mycoplasma genitalium, Ureaplasma urealyticum, Trichomonas vaginalis, HSV |
| Epididymitis | C. trachomatis, N. gonorrhoeae, HSV |
| Lower genital tract infections: females | C. trachomatis, N. gonorrhoeae, HSV, HSV, some anaerobic bacteria, Leptotrichia/Sneathia |
| Vulvovaginitis | Candida albicans, HSV, T. vaginalis, BV-associated bacteria |
| Acute pelvic inflammatory disease | N. gonorrhoeae, C. trachomatis, BV-associated bacteria, M. genitalium, group B streptococci |
| Complications of pregnancy/puerperium | Several pathogens implicated |
| Intestinal infections | Proctitis, proctocolitis, enteritis |
| Hepatitis | Hepatitis viruses, T. pallidum, CMV, EBV |
| SYNDROME | SEXUALLY TRANSMITTED MICROBIAL ETIOLOGIES |
|---|---|
| Neoplasias | Squamous cell dysplasias, cervical cancer, hepatocellular carcinoma, Kaposi’s sarcoma, body-cavity lymphomas, T-cell leukemia, hepatocellular carcinoma, tropical spastic paraparesis, scabies, pubic lice |
2.1 Incidence and Prevalence¶
Globally, STIs are the most common infectious diseases. In the U.S., the CDC reports annual incidence rates for gonorrhea, chlamydia, and syphilis. Chlamydeal infections are most common, with 457.6 cases per 100,000 in 2011. Syphilis incidence peaked in the 1940s but declined until the 1990s, with a resurgence among MSM.
2.2 Risk Factors¶
Risk factors include multiple sexual partners, transactional sex, and substance use. In the U.S., chlamydia prevalence is highest among young women, with 15% of women aged 14–19 having chlamydia. HIV prevalence is higher among MSM and in populations with limited access to healthcare.
3. ETIOLOGY & PATHOPHYSIOLOGY¶
STIs are caused by diverse pathogens, including bacteria, viruses, and parasites. Pathogenesis varies by agent, with some (e.g., HIV) causing chronic infection and others (e.g., gonorrhea) leading to acute symptoms. Pathogens like HPV and HSV can cause persistent infections with oncogenic potential.
Table 141-3: Eleven-Question Sexually Transmitted Disease (STD)/HIV Risk Assessment¶
| Framing Statemen t | Screenin g Questio ns | STD History | Sexual Pr eference | Injection Drug Use | Characte ristics of Partner(s ) | STD Sym ptoms Checklist | Sexual Pr actices, Past 2 Months | Query About Interest in STD S creening Tests |
|---|---|---|---|---|---|---|---|---|
| In order to provide the best care for you today and to un derstand whether we should consider certain infections, I’d like to talk about your sexual behavior. | Do you have any reason to think you might have a sexually tr ansmitted infection? If so, what reason? | Have you ever had any sexually tr ansmitted infections or any genital inf ections? If so, which ones? | Have you had sex with men, women, or both? | Have you ever injected yourself with drugs? (If yes, have you ever shared needles or injection e quipment ?) | Have any of your sex partners had any sexually tr ansmitted infections ? If so, which ones? | Have you recently developed any of these sym ptoms? | For Men For Women | Would you like to be tested for HIV or any other STDs today? (If yes, clinician can explore which STD and why.) |
3.1 Bacterial Pathogens¶
Neisseria gonorrhoeae, Chlamydia trachomatis, and Treponema pallidum are major bacterial causes. Mycoplasma genitalium and Ureaplasma urealyticum are increasingly recognized as contributors to urethritis and pelvic inflammatory disease (PID).
3.2 Viral Pathogens¶
HIV, herpes simplex virus (HSV), and human papillomavirus (HPV) are leading viral causes. HPV types 16 and 18 are oncogenic, contributing to cervical cancer. HSV causes recurrent genital ulcers and increases HIV transmission risk.
4. CLINICAL FEATURES¶
Clinical manifestations vary by STI, with common symptoms including genital discharge, ulcers, pain, and systemic symptoms. Complications include infertility, HIV transmission, and malignancies. Early diagnosis is critical to prevent long-term sequelae.
Table 141-4: Management of Urethral Discharge in Men¶
| USUAL CAUSES | USUAL INITIAL EVALUATION | INITIAL TREATMENT FOR PATIENT AND PARTNERS |
|---|---|---|
| Chlamydia trachomatis | Demonstration of urethral discharge or pyuria | Ceftriaxone (500 mg IMa) |
| Neisseria gonorrhoeae | Exclusion of local or systemic complications | For persons weighing ‡150 kg, 1 gram of ceftriaxone IM should be administered |
| Mycoplasma genitalium | Urethral Gram’s stain to confirm urethritis, detect gram-negative diplococci | Metronidazole or tinidazole (2 g by mouth in a single dose) |
| Ureaplasma urealyticum | Test for N. gonorrhoeae, C. trach, M. genitalium (if indicated and available) | Doxycycline (100 mg PO bid for 14 days) |
| Trichomonas vaginalis | Test for N. gonorrhoeae, C. trach, M. genitalium (if indicated and available) | Metronidazole (500 mg PO bid for 7 days) |
| Herpes simplex virus | Demonstration of urethral discharge or pyuria | Acyclovir, valacyclovir, or famciclovir |
4.1 Common Symptoms¶
Genital discharge, ulcers, pain, and systemic symptoms (e.g., fever) are common. Specific syndromes include urethritis, cervicitis, and PID. Symptoms may be nonspecific, requiring careful evaluation.
4.2 Complications¶
Untreated STIs can lead to infertility, HIV transmission, and malignancies (e.g., cervical cancer from HPV). PID is a major complication of untreated chlamydia or gonorrhea, leading to ectopic pregnancy and infertility.
5. DIFFERENTIAL DIAGNOSIS¶
Differential diagnosis includes non-STI conditions like bacterial vaginosis, yeast infections, and dermatological conditions. Accurate diagnosis requires clinical evaluation, laboratory tests, and patient history.
Table 141-5: Diagnostic Features and Management of Vaginal Infection¶
| FEATURE | NORMAL VAGINAL EXAMINATION | VULVOVAGINAL CANDIDIASIS | TRICHOMONAL VAGINITIS | BACTERIAL VAGINOSIS (BV) |
|---|---|---|---|---|
| Etiology | Uninfected; lactobacilli predominant | Candida albicans | Trichomonas vaginalis | Associated with Gardnerella vaginalis, various anaerobic bacteria, and mycoplasmas |
| Typical symptoms | None | Vulvar itching and/or irritation | Profuse discharge; vulvar itching | Malodorous, slightly increased discharge |
| Discharge | Variable; usually scant | Scant | Often profuse | Moderate |
| Colora | Clear or translucent | White | White or yellow | White or gray |
| Consistency | Nonhomogeneous, flocculent | Clumped; adherent plaques | Homogeneous | Homogeneous, low viscosity; uniformly |
| Inflammation of vulvar or vaginal epithelium | None | Erythema of vaginal epithelium, introitus; vulvar dermatitis, fissures | Erythema of vaginal and vulvar epithelium; colpitis macularis | None |
| pH of vaginal fluidb | Usually £4.5 | Usually £4.5 | Usually ‡5 | Usually >4.5 |
| Amine ("fishy") odor | None | None | May be present | Present |
| Microscopyc | Normal epithelial cells; lactobacilli predominant | Leukocytes, epithelial cells; mycelia | Leukocytes; motile trichomonads | Clue cells; few leukocytes; no lactobacilli or only a few outnumbered by profuse mixed microbiota, nearly always including G. vaginalis plus anaerobic species on Gram’s stain (Nugent’s score ‡7) |
5.1 Common Mimics¶
Bacterial vaginosis, yeast infections, and dermatological conditions (e.g., psoriasis, eczema) can mimic STIs. Accurate diagnosis requires clinical evaluation, laboratory tests, and patient history.
5.2 Diagnostic Approach¶
Clinical evaluation, laboratory tests (e.g., NAAT, Gram stain), and patient history are essential. Specific tests for pathogens like HSV, HPV, and HIV are critical for accurate diagnosis.
6. INVESTIGATIONS & DIAGNOSIS¶
Diagnosis of STIs requires a combination of clinical evaluation, laboratory tests, and imaging. Key tests include nucleic acid amplification tests (NAAT), Gram stain, and serology for syphilis.
Table 141-6: Combination Antimicrobial Regimens Recommended for Outpatient Treatment or for Parenteral Treatment of Pelvic Inflammatory Disease¶
| OUTPATIENT REGIMENSa | PARENTERAL REGIMENS |
|---|---|
| Ceftriaxone (500 mg IM once) plus | Initiate parenteral therapy with either of the following regimens; continue parenteral therapy until 48 h after clinical improvement; then change to outpatient therapy, as described in the text |
| Doxycycline (100 mg PO bid for 14 days) plus | Regimen A: Cefotetan (2 g IV q12h) or cefoxitin (2 g IV q6h) plus Doxycycline (100 mg IV or PO q12h) |
| Metronidazole (500 mg PO bid for 14 days) | Regimen B: Clindamycin (900 mg IV q8h) plus Gentamicin (loading dose of 2 mg/kg IV or IM, then maintenance dose of 1.5 mg/kg q8h) |
6.1 Diagnostic Tests¶
NAAT, Gram stain, and serology are essential for diagnosing STIs. Specific tests for pathogens like HSV, HPV, and HIV are critical for accurate diagnosis.
6.2 Imaging¶
Imaging is used for complications like PID or pelvic abscesses. Ultrasound and MRI may be required to assess pelvic structures.
7. MANAGEMENT & TREATMENT¶
Treatment of STIs involves antimicrobial therapy, partner management, and prevention strategies. Early treatment is critical to prevent complications and reduce transmission.
Table 141-7: Clinical Features of Genital Ulcers¶
| FEATURE | LYMPHOGRAN ULOMA VENEREUM | SYMPHILIS | HERPES | CHANCROID | DONOVANOSIS |
|---|---|---|---|---|---|
| Incubation period | 9–90 days | 2–7 days | 1–14 days | 3 days–6 weeks | 1–4 weeks (up to 6 months) |
| Early primary lesions | Papule | Vesicle | Pustule | Papule, pustule, or vesicle | Papule |
| Number of lesions | Usually one | Multiple | Usually multiple, may coalesce | Usually one; often not detected, despite lymphad enopathy | Variable |
| Diameter | 5–15 mm | 1–2 mm | Variable | 2–10 mm | Variable |
| Edges | Sharply demarcated, elevated, round, or oval | Erythematous | Undermined, ragged, irregular | Elevated, round, or oval | Elevated, irregular |
| Depth | Superficial or deep | Superficial | Excavated | Superficial or deep | Elevated |
| Base | Smooth, nonpurulent, relatively nonvascular | Serous, erythematous, nonvascular | Purulent, bleeds easily | Variable, nonvascular | Red and velvety, bleeds readily |
| Induration | Firm | None | Soft | Occasionally firm | Firm |
| FEATURE | LYMPHOGRAN ULOMA VENEREUM | SYMPHILIS | HERPES | CHANCROID | DONOVANOSIS |
|---|---|---|---|---|---|
| Pain | Uncommon | Frequently tender | Usually very tender | Variable | Uncommon |
| Lymphadenopat hy | Firm, nontender, bilateral | Firm, tender, often bilateral with initial episode | Tender, may suppurate, loculated, usually unilateral | Tender, may suppurate, loculated, usually unilateral |
7.1 Antimicrobial Therapy¶
Antibiotics, antivirals, and antifungals are used based on the causative agent. For example, doxycycline for chlamydia, metronidazole for bacterial vaginosis, and acyclovir for HSV.
7.2 Partner Management¶
All sexual partners should be tested and treated to prevent reinfection. Partner notification is a critical component of STI management.
8. PROGNOSIS & COMPLICATIONS¶
Untreated STIs can lead to severe complications, including infertility, HIV transmission, and malignancies. Early diagnosis and treatment are critical to prevent long-term sequelae.
Table 141-8: Initial Management of Genital or Perianal Ulcer¶
| CAUSATIVE PATHOGENS | USUAL INITIAL LABORATORY EVALUATION | INITIAL TREATMENT |
|---|---|---|
| HSV | Dark-field examination (if available), direct FA, or PCR for T. pallidum | Treat for genital herpes with acyclovir, valacyclovir, or famciclovir |
| Treponema pallidum (primary syphilis) | RPR, VDRL, or EIA serologic test for syphilisa | Benzathine penicillin (2.4 million units IM once to patient, to recent [e.g., within 3 months] seronegative partner[s], and to all recent partners)b |
| Haemophilus ducreyi (chancroid) | Culture, direct FA, ELISA, or PCR for HSV | Ciprofloxacin (500 mg PO as single dose) or Ceftriaxone (250 mg IM as single dose) or Azithromycin (1 g PO as single dose) |
8.1 Long-Term Effects¶
Chronic STIs like HIV and HSV can lead to progressive disease and complications. Untreated chlamydia or gonorrhea can cause PID, leading to infertility and ectopic pregnancy.
8.2 Prevention¶
Vaccination (e.g., HPV), safe sex practices, and regular screening are essential to prevent STIs and their complications.
9. SPECIAL CONSIDERATIONS¶
Special considerations include pregnancy, pediatric populations, and elderly patients. Management may vary based on age, comorbidities, and medication interactions.
Table 141-9: Critical Control Points for Preventive and Clinical Interventions Against STIs¶
| Numbe r whose behavi ors and ec ologic setting s result in expo sure to STDs | Numbe r who a cquire STDs | Numbe r who develo p symp toms of STDs | Numbe r who perceiv e the s ympto ms of STDs | Numbe r who prompt ly seek medica l care when s ympto matic | Numbe r seeki ng care who have ready access to care | Numbe r perce ived by clinicia ns as p ossibly having STDs | Numbe r perce ived as possibl y having STDs who can be tested for STDs | Numbe r with objecti ve evid ence of STDs who get proper treatm ent | Numbe r who comply with tr eatmen t | Numbe r whose partner s are treated and who are not reinfec ted |
|---|---|---|---|---|---|---|---|---|---|---|
9.1 Pregnancy¶
STIs during pregnancy can lead to complications like preterm birth and congenital infections. Screening and treatment are critical to prevent vertical transmission.
9.2 Pediatrics¶
Children may present with atypical symptoms. Diagnosis requires careful evaluation, as many STIs are asymptomatic in pediatric populations.
10. KEY POINTS & CLINICAL PEARLS¶
Key points include the importance of screening, the role of sexual behavior in STI transmission, and the necessity of partner management. Clinical pearls emphasize early diagnosis and the use of NAAT for accurate detection.