# Sexually Transmitted Infections and Pelvic Inflammatory Disease

## Introduction

Sexually transmitted infections (STIs) are a major public health concern with over 26 million new infections annually in the United States. The emergency physician plays a critical role in the diagnosis, empiric treatment, and public health management of STIs. Pelvic inflammatory disease (PID), a serious sequela of untreated STIs, can lead to infertility, ectopic pregnancy, and chronic pelvic pain if not identified and treated early.

## Chlamydia and Gonorrhea

### Chlamydia (Chlamydia trachomatis)

Chlamydia is the most commonly reported bacterial STI in the United States, with the highest prevalence in females aged 15 to 24. It is often asymptomatic, with up to 70 percent of women and 50 percent of men having no symptoms. When symptomatic, it presents as mucopurulent cervicitis, urethritis (with dysuria and discharge), or proctitis. Complications include PID, tubal factor infertility, ectopic pregnancy, and reactive arthritis. Diagnosis is made by nucleic acid amplification test (NAAT) on urine, cervical swab, vaginal swab, or rectal/pharyngeal swab. Treatment is doxycycline 100 mg orally twice daily for 7 days, which is now preferred over azithromycin per the 2021 CDC guidelines because of its superior efficacy for rectal chlamydia.

### Gonorrhea (Neisseria gonorrhoeae)

Gonorrhea is the second most commonly reported bacterial STI and frequently co-occurs with chlamydia, with a co-infection rate of 10 to 30 percent. It presents with purulent urethral discharge, cervicitis, pharyngitis (often asymptomatic), and proctitis. Disseminated gonococcal infection (DGI) manifests as a triad of dermatitis (pustular skin lesions), polyarthralgias, and tenosynovitis, and may progress to purulent septic arthritis. Diagnosis relies on NAAT as the primary modality, though culture is needed for antimicrobial susceptibility testing. Treatment is ceftriaxone 500 mg IM as a single dose (1 gram IM if the patient weighs 150 kg or more). Co-treatment for chlamydia with doxycycline should always be given unless NAAT has excluded co-infection. Antimicrobial resistance is an emerging threat, with fluoroquinolone resistance now widespread, and CDC guidelines should be monitored for updates.

## Syphilis (Treponema pallidum)

### Stages

Primary syphilis presents with a painless chancre, which is an indurated ulcer with a clean base at the site of inoculation, appearing 10 to 90 days after exposure. It is highly infectious and heals spontaneously in 3 to 6 weeks. Secondary syphilis produces a diffuse maculopapular rash characteristically involving the palms and soles, condylomata lata (moist, gray-white plaques in intertriginous areas), mucous patches, generalized lymphadenopathy, and constitutional symptoms. Latent syphilis is asymptomatic and is divided into early latent (less than 1 year) and late latent (more than 1 year or unknown duration). Tertiary syphilis manifests as gummatous disease, cardiovascular syphilis (aortitis), or neurosyphilis (tabes dorsalis, general paresis, Argyll Robertson pupil).

### Diagnosis

The screening algorithm now commonly uses a reverse sequence: an initial EIA or CIA (treponemal test) is confirmed with RPR or VDRL (non-treponemal test). RPR and VDRL are quantitative and are used to monitor treatment response, with a four-fold decline expected after successful treatment. Darkfield microscopy can detect spirochetes from chancre exudate but is rarely available in the ED.

### Treatment

| STI | Recommended Treatment (CDC 2021) | Alternative |
|-----|----------------------------------|-------------|
| Chlamydia | Doxycycline 100 mg PO BID x 7 days | Azithromycin 1 g PO x 1 |
| Gonorrhea | Ceftriaxone 500 mg IM x 1 (1 g if ≥150 kg) + treat chlamydia | — |
| Primary/Secondary/Early latent syphilis | Benzathine penicillin G 2.4 MU IM x 1 | Doxycycline 100 mg PO BID x 14 days |
| Late latent syphilis | Benzathine penicillin G 2.4 MU IM weekly x 3 doses | — |
| Neurosyphilis | Aqueous penicillin G 18–24 MU/day IV x 10–14 days | — |
| Genital herpes (primary) | Valacyclovir 1 g PO BID x 7–10 days | Acyclovir 400 mg PO TID x 7–10 days |
| PID (outpatient) | Ceftriaxone 500 mg IM + doxycycline 100 mg PO BID x 14 days + metronidazole 500 mg PO BID x 14 days | — |

Primary, secondary, and early latent syphilis are treated with benzathine penicillin G 2.4 million units IM as a single dose. Late latent syphilis or syphilis of unknown duration requires benzathine penicillin G 2.4 million units IM weekly for 3 doses. Neurosyphilis requires aqueous crystalline penicillin G 18 to 24 million units per day IV for 10 to 14 days. The Jarisch-Herxheimer reaction, which manifests as fever, chills, and myalgias within 24 hours of treatment, is caused by spirochete lysis and is self-limited. It is managed with antipyretics.

<image>Clinical illustration showing the progression of syphilis stages: primary chancre (painless ulcer on genital mucosa), secondary syphilis (diffuse rash with palmar and plantar involvement, condylomata lata), and tertiary manifestations (gumma, aortic aneurysm), arranged in a timeline format</image>

## Genital Herpes (HSV-1 and HSV-2)

HSV-2 is the most common cause of recurrent genital ulcers, though HSV-1 genital infections are increasingly prevalent. The primary outbreak presents with multiple painful vesicular or ulcerative lesions, bilateral inguinal lymphadenopathy, and systemic symptoms (fever, malaise), and may last 2 to 3 weeks. Recurrent outbreaks are shorter and less severe, often preceded by prodromal tingling or burning. Diagnosis is made by HSV PCR (preferred) or viral culture from vesicle fluid, with type-specific serology used for chronic or recurrent cases. Treatment of primary outbreaks is valacyclovir 1 gram orally twice daily for 7 to 10 days, and recurrent outbreaks are treated with 500 mg orally twice daily for 3 to 5 days. Acyclovir 400 mg orally three times daily is an alternative. Suppressive therapy with valacyclovir 500 mg to 1 gram orally daily is indicated for frequent recurrences (6 or more per year) or serodiscordant couples.

## Genital Ulcer Disease -- Differential Diagnosis

Painless ulcers suggest syphilis (chancre) or lymphogranuloma venereum (LGV). Painful ulcers are most commonly caused by HSV, with chancroid (Haemophilus ducreyi) being rare in the United States but presenting with a painful, ragged ulcer with a purulent base and tender inguinal lymphadenopathy. Multiple etiologies can coexist, so patients with genital ulcers should be tested broadly with RPR, HSV PCR, and HIV testing.

## Pelvic Inflammatory Disease

### Definition and Microbiology

PID is an infection of the upper female genital tract encompassing endometritis, salpingitis, tubo-ovarian abscess (TOA), and pelvic peritonitis. It results from ascending infection from the cervix. N. gonorrhoeae and C. trachomatis are the most commonly identified organisms, but anaerobes, gram-negative rods, and Mycoplasma genitalium also contribute. Risk factors include age 15 to 25, multiple sexual partners, prior STIs, IUD insertion within the prior 3 weeks, and douching.

### Clinical Presentation

Lower abdominal pain is the most common symptom. Other features include abnormal vaginal or cervical discharge, irregular vaginal bleeding, and dyspareunia. Examination findings include cervical motion tenderness (CMT), uterine tenderness, and adnexal tenderness. Systemic signs such as fever and elevated WBC are present in only a minority of cases.

### Diagnostic Criteria (CDC 2021)

The minimum criteria for empiric treatment are a sexually active young woman with pelvic or lower abdominal pain and at least one of cervical motion tenderness, uterine tenderness, or adnexal tenderness, with no other identifiable cause. Supportive criteria include oral temperature above 38.3 degrees Celsius, abnormal cervical mucopurulent discharge, abundant WBCs on wet mount, elevated ESR or CRP, and laboratory documentation of cervical gonorrhea or chlamydia infection. The threshold for treatment should be low because the consequences of untreated PID (infertility, ectopic pregnancy, chronic pain) outweigh the risks of empiric antibiotics.

<image>Anatomical illustration of the female reproductive tract showing the ascending path of infection in PID, from the cervix through the endometrium to the fallopian tubes, with labeled complications including endometritis, salpingitis, tubo-ovarian abscess, and pelvic peritonitis with adhesion formation</image>

### Imaging

Transvaginal ultrasound is the first-line imaging modality for suspected TOA, with findings including a complex adnexal mass, a thick-walled fluid collection, and pyosalpinx (a dilated, fluid-filled fallopian tube). CT of the abdomen and pelvis is useful when the diagnosis is uncertain or to evaluate alternative etiologies such as appendicitis or ovarian torsion.

### Treatment

Outpatient treatment for mild to moderate PID consists of ceftriaxone 500 mg IM as a single dose plus doxycycline 100 mg orally twice daily for 14 days plus metronidazole 500 mg orally twice daily for 14 days. Inpatient treatment is indicated when a surgical emergency cannot be excluded, when a TOA is present, during pregnancy, when severe illness or nausea and vomiting preclude oral therapy, or when outpatient therapy has failed. The inpatient regimen is cefotetan 2 grams IV every 12 hours (or cefoxitin 2 grams IV every 6 hours) plus doxycycline 100 mg orally or IV every 12 hours, with transition to oral therapy after 24 to 48 hours of clinical improvement. TOAs are managed with IV antibiotics, with interventional radiology or surgical drainage if there is no response to 48 to 72 hours of antibiotics. A ruptured TOA is a surgical emergency.

## Partner Notification and Reporting

Gonorrhea, chlamydia, and syphilis are reportable diseases in all US states. Expedited partner therapy (EPT) allows providing prescriptions or medications for the patient's sexual partners without a clinical examination and is legal in most states. All patients diagnosed with one STI should be tested for coexisting infections including HIV, syphilis, and hepatitis B and C. Rescreening in 3 months is recommended for patients treated for gonorrhea or chlamydia because of high reinfection rates.

<image>Infographic summarizing CDC-recommended treatment algorithms for common STIs: chlamydia (doxycycline), gonorrhea (ceftriaxone), syphilis (benzathine penicillin G), genital herpes (valacyclovir), and PID (ceftriaxone + doxycycline + metronidazole), with dosing and duration for each</image>

## Clinical Pearls

Co-treatment for chlamydia should always accompany gonorrhea treatment unless NAAT has excluded co-infection. PID should be treated empirically based on minimal clinical criteria because a high threshold for diagnosis leads to missed cases and preventable infertility. Syphilis is the "great imitator" and should be considered in any patient with an unexplained rash involving the palms and soles. All patients diagnosed with an STI should be tested for HIV. Ceftriaxone has replaced cefixime as the recommended treatment for gonorrhea due to rising resistance.

## References

1. Workowski KA, Bachmann LH, Chan PA, et al. Sexually transmitted infections treatment guidelines, 2021. *MMWR Recomm Rep*. 2021;70(4):1-187.
2. Brunham RC, Gottlieb SL, Paavonen J. Pelvic inflammatory disease. *N Engl J Med*. 2015;372(21):2039-2048.
3. Hook EW III. Syphilis. *Lancet*. 2017;389(10078):1550-1557.
4. St Cyr S, Barbee L, Workowski KA, et al. Update to CDC's treatment guidelines for gonococcal infection, 2020. *MMWR Morb Mortal Wkly Rep*. 2020;69(50):1911-1916.