Here we present an updated STI “cheat sheet” for some of the infections and syndromes most commonly encountered in the Emergency Department: how they present, what to test, and what to treat.
The following recommendations are based primarily on the current Public Health Agency of Canada (PHAC) Sexually Transmitted and Blood-Borne Infection (STBBI) Guidelines, supplemented by other contemporary guidelines where PHAC does not provide specific treatment recommendations.
This is not intended to replace a comprehensive sexual history. Before deciding what to test, remember that the sites you test should reflect the sites that were exposed. A urine NAAT is not a universal STI screen.
Genital Herpes
Genital herpes is caused by HSV-1 or HSV-2. Either type can cause genital infection, although HSV-2 is more likely to cause recurrent genital disease.
Clinical presentation
The classic presentation is painful, grouped vesicles that evolve into shallow ulcers on an erythematous base. Burning, itching or pain may precede the lesions. Tender inguinal lymphadenopathy is particularly common with primary infection, and patients may also have dysuria, fever, malaise or more extensive disease.
Importantly, appearances vary considerably and clinical diagnosis alone is imperfect.
Diagnosis
In patients with active lesions, NAAT/PCR from the lesion is preferred where available. Viral culture is less sensitive, particularly once lesions have begun healing. Routine HSV serologic screening is not recommended in asymptomatic people without a history of anogenital lesions.
Treatment
Treatment does not eradicate HSV, but decreases symptom duration, viral shedding and time to lesion healing.
First episode:
- Valacyclovir 1,000 mg PO BID × 10 days
Alternatives include acyclovir 200 mg PO five times daily × 5–10 days or famciclovir 250 mg PO TID × 5 days.
Treat a first episode unless all lesions have already healed.
Recurrent episode:
- Valacyclovir 500 mg PO BID × 3 days, OR
- Valacyclovir 1,000 mg PO daily × 3 days
Treatment is most effective when started during the prodrome or very early after lesion onset.
Important points
Asymptomatic viral shedding occurs and transmission can occur in the absence of visible lesions. Condoms reduce, but do not eliminate, transmission risk because HSV can involve skin not covered by a condom.
Consider suppressive therapy in patients with frequent or particularly troublesome recurrences or when reducing transmission is an important priority.
Severe complications include aseptic meningitis/encephalitis, hepatitis, pneumonitis, disseminated infection and neurologic complications.
Syphilis
Syphilis is caused by the spirochete Treponema pallidum. Its clinical presentation varies substantially by stage.
Primary syphilis
Classically presents with a painless, indurated, clean-based chancre at the site of inoculation. Regional lymphadenopathy may occur. Importantly, primary lesions are not always textbook.
Secondary syphilis
Occurs weeks to months after primary infection and may produce a diffuse rash, classically involving the palms and soles, generalized lymphadenopathy, fever and constitutional symptoms, mucous patches, condylomata lata and patchy alopecia.
Latent syphilis
There are no clinical manifestations. PHAC defines early latent syphilis as infection acquired within the preceding 12 months. Late latent syphilis refers to infection acquired more than 12 months previously or of unknown duration.
Tertiary syphilis
Late manifestations can include cardiovascular syphilis and gummatous disease.
Neurosyphilis
Neurosyphilis can occur at any stage of syphilis. Manifestations include meningitis, cranial neuropathies, stroke, altered mental status, sensory abnormalities, ocular disease and otosyphilis.
Diagnosis: Understanding the serology
Most Canadian laboratories use a reverse-sequence algorithm. A treponemal antibody assay such as EIA/CMIA is performed first. If reactive, a quantitative non-treponemal test, usually RPR, is performed. A second treponemal test such as TP-PA may be used to resolve discordant results.
Treponemal test = Is there serologic evidence of current or previous infection with syphilis?
Treponemal tests generally remain reactive indefinitely after infection and therefore should not be used to monitor treatment.
RPR = What is the titre, and how is it changing?
RPR titres are used for follow-up. A clinically meaningful change is generally a fourfold change. For example, 1:32 → 1:8 represents a fourfold decrease, while 1:4 → 1:16 represents a fourfold increase.
Serology may still be negative during very early primary syphilis. If clinical suspicion is high, repeat serology and consider direct testing of the lesion where available.
Treatment
Primary, secondary and early latent syphilis:
- Benzathine penicillin G-LA 2.4 million units IM × 1
Late latent or tertiary syphilis without neurosyphilis:
- Benzathine penicillin G-LA 2.4 million units IM weekly × 3 doses
Suspected neurosyphilis:
Consult Infectious Diseases/Neurology. Neurosyphilis requires CNS-penetrating IV penicillin rather than benzathine penicillin alone. A commonly recommended regimen is aqueous crystalline penicillin G 3–4 million units IV q4h for 10–14 days.
Chancroid
Chancroid is an ulcerative STI caused by Haemophilus ducreyi. It is uncommon in Canada and should generally prompt consideration of alternative causes of genital ulceration, particularly HSV and syphilis.
Presentation
Classically, chancroid causes a painful genital ulcer with irregular borders and an inflamed or purulent base. Tender regional lymphadenopathy may occur. Nodes may suppurate and form a bubo.
Diagnosis
Clinical appearance alone is not sufficiently reliable to distinguish chancroid from other causes of genital ulceration. Testing availability for H. ducreyi is limited.
Any patient presenting with an anogenital ulcer should also be evaluated for more common causes, particularly HSV and syphilis.
Treatment
Chancroid is rare in Canada. If suspected, obtain appropriate testing and discuss treatment with an experienced colleague. Commonly recommended regimens internationally include azithromycin 1 g PO once or ceftriaxone 250 mg IM once.
Trichomoniasis
Trichomoniasis is caused by Trichomonas vaginalis. Many infections are asymptomatic.
Presentation
When symptomatic, patients may have vaginal irritation or pruritus, dysuria, dyspareunia, vaginal discharge or postcoital bleeding.
The classic description is a frothy yellow-green discharge, sometimes accompanied by a “strawberry cervix,” although neither finding is sufficiently sensitive to rule the diagnosis in or out.
Diagnosis
NAAT is preferred where available.
Treatment
- Metronidazole 500 mg PO BID × 7 days, OR
- Metronidazole 2 g PO × 1 dose
Current sexual partners should also be treated. Intravaginal metronidazole gel is not effective treatment for trichomoniasis.
Gonorrhea
Gonorrhea is caused by the gram-negative diplococcus Neisseria gonorrhoeae. Infection may occur at genital, rectal or pharyngeal sites and is frequently asymptomatic.
Clinical presentations
Depending on the site, gonorrhea can present as urethritis, cervicitis, PID, epididymitis, proctitis, pharyngitis or conjunctivitis.
Disseminated gonococcal infection
Consider DGI in patients with combinations of fever, migratory polyarthralgia, tenosynovitis, pustular or petechial skin lesions and septic arthritis. Less commonly, gonococcal infection can cause endocarditis or meningitis.
Diagnosis
NAAT is the preferred diagnostic test. The specimen should reflect the patient’s anatomy and sites of exposure.
Depending on the history, testing may include:
- First-void urine
- Vaginal/cervical swab
- Pharyngeal swab
- Rectal swab
A negative urine NAAT does not exclude pharyngeal or rectal gonorrhea.
Culture remains important when antimicrobial resistance or treatment failure is suspected because it permits susceptibility testing.
Treatment
Current PHAC preferred therapy for all uncomplicated gonococcal infections, including urethral, endocervical, vaginal, rectal and pharyngeal infection, is:
- Ceftriaxone 500 mg IM × 1
Routine azithromycin is no longer added to ceftriaxone.
If chlamydia has not been excluded, concurrently treat for chlamydia:
- Doxycycline 100 mg PO BID × 7 days
Why the change?
Gonorrhea has demonstrated a remarkable ability to develop antimicrobial resistance. Increasing ceftriaxone from the older 250 mg regimen to 500 mg provides better pharmacokinetic coverage against organisms with reduced susceptibility.
Routine azithromycin was removed because of increasing azithromycin resistance, antimicrobial stewardship concerns and the absence of a clear benefit to routine dual therapy.
Test of cure
PHAC currently recommends test of cure for all positive gonorrhea sites. When possible, culture can be performed ≥3 days after treatment. If NAAT is used, it should generally be performed ≥3–4 weeks after treatment to avoid detecting residual nucleic acid.
Chlamydia
Chlamydia is caused by Chlamydia trachomatis and is frequently asymptomatic.
When symptomatic, it may cause urethritis, cervicitis, PID, epididymitis or proctitis.
Diagnosis
NAAT is the preferred test. Test the site that was exposed. Depending on the sexual history this may include first-void urine, vaginal/cervical swab, rectal swab or pharyngeal swab.
Treatment
For uncomplicated anogenital infection in non-pregnant/non-lactating adults:
- Doxycycline 100 mg PO BID × 7 days, OR
- Azithromycin 1 g PO × 1 dose
Azithromycin remains an accepted PHAC regimen and may be useful when adherence to seven days of doxycycline is a concern.
Follow-up
Routine test of cure is not required for uncomplicated chlamydia in most non-pregnant patients who received appropriate therapy and whose symptoms resolve.
Repeat screening at approximately 3 months is recommended because reinfection is common.
Gonorrhea: Did we cure it? → Test of cure.
Chlamydia: Did they get it again? → Retest for reinfection.
Lymphogranuloma Venereum (LGV)
LGV is caused by the more invasive L1, L2 and L3 serovars of Chlamydia trachomatis. Unlike typical chlamydial infection, LGV invades deeper tissues and regional lymphatics.
Presentation
LGV can present with proctitis/proctocolitis, severe rectal pain, tenesmus, bloody or purulent rectal discharge, rectal ulceration, constipation, inguinal or femoral lymphadenopathy and buboes.
Contemporary Canadian cases have occurred predominantly among gbMSM.
Diagnosis
A routine rectal chlamydia NAAT detects C. trachomatis but does not necessarily distinguish ordinary D–K serovars from LGV. Definitive diagnosis requires LGV genotyping.
Suspect LGV when a patient has a positive rectal chlamydia test with a compatible syndrome, particularly severe proctitis.
Treatment
Do not wait for genotyping when the clinical syndrome is strongly suggestive.
- Doxycycline 100 mg PO BID × 21 days
Proctitis
Proctitis is inflammation of the rectal mucosa and should be considered in patients with rectal pain, tenesmus, rectal discharge, bleeding or painful defecation.
Sexually transmitted proctitis may follow receptive anal sex, oral-anal contact or digital-anal contact.
Think beyond gonorrhea and chlamydia
The differential includes gonorrhea, chlamydia including LGV, HSV, syphilis, mpox and Mycoplasma genitalium. Depending on the exposure and presentation, enteric pathogens such as Shigella and Campylobacter may also need consideration.
Testing
Depending on the presentation, testing may include:
- Rectal GC/CT NAAT
- Gonorrhea culture where indicated
- Syphilis serology
- HIV testing
- HSV NAAT from ulcers or lesions
- Mpox testing where clinically indicated
Severe proctitis with a positive rectal chlamydia NAAT should raise concern for LGV.
Pelvic Inflammatory Disease
PID represents ascending infection and inflammation involving the upper female reproductive tract. It is frequently polymicrobial. Gonorrhea and chlamydia are important causes, but they are not the only organisms involved.
PID is a clinical diagnosis.
Have a low threshold to treat when the clinical syndrome is compatible.
Findings supporting PID include:
- Cervical motion tenderness
- Uterine tenderness
- Adnexal tenderness
- Mucopurulent cervical discharge
- Cervical friability
- Fever
- Elevated inflammatory markers
- Positive GC/CT testing
However:
A normal WBC does not exclude PID.
Negative GC/CT testing does not exclude PID.
A normal ultrasound does not exclude PID.
Do not use a negative test for gonorrhea or chlamydia to answer a different question: “Does this patient have PID?”
Outpatient treatment
- Ceftriaxone 500 mg IM × 1
- PLUS doxycycline 100 mg PO BID × 14 days
- PLUS metronidazole 500 mg PO BID × 14 days
Consider hospitalization when:
- Pregnancy
- Tubo-ovarian abscess
- A surgical emergency cannot be excluded
- Severe illness, significant pain, vomiting or high fever
- Unable to tolerate or adhere to outpatient treatment
- Immunocompromised
- No clinical response within 2–3 days
PID itself does not automatically require admission.
Epididymitis
Acute epididymitis typically presents with unilateral scrotal pain, swelling and epididymal tenderness.
First: Don’t miss torsion
Before deciding which organism caused epididymitis, determine whether the presentation could represent testicular torsion. If torsion is clinically plausible, do not delay appropriate imaging or urologic assessment while waiting for STI testing.
What causes epididymitis?
Avoid the old teaching of “Young = STI, old = E. coli.”
The likely pathogen is better determined by sexual practices, STI risk factors and urinary tract risk factors.
Chlamydia and gonorrhea are common causes in sexually active patients. Enteric organisms become particularly relevant with urinary tract pathology/instrumentation and following insertive anal intercourse.
Testing
Obtain GC/CT NAAT and urinalysis/urine culture where appropriate.
Treatment
When gonorrhea/chlamydia are suspected:
- Ceftriaxone 500 mg IM × 1 PLUS doxycycline 100 mg PO BID × 10–14 days
When STI infection and enteric organisms are suspected, such as after condomless insertive anal intercourse:
- Ceftriaxone 500 mg IM × 1 PLUS levofloxacin 500 mg PO daily × 10 days
Bacterial Vaginosis
Bacterial vaginosis represents a shift in the vaginal microbiome with depletion of lactobacilli and overgrowth of other organisms.
BV is not conventionally considered an STI.
Presentation
Typical features include thin, homogeneous grey-white discharge and a fishy odour. Significant vulvar inflammation, marked pruritus or external dysuria should prompt consideration of an alternative or additional diagnosis.
Diagnosis
The Amsel criteria are:
- Homogeneous, thin discharge
- Vaginal pH >4.5
- Presence of clue cells on microscopy
- Positive whiff test
Three of four criteria support the diagnosis.
NAAT-based molecular testing is also increasingly available.
Culture is not the gold standard and is not recommended for routine diagnosis, because organisms associated with BV can be present in patients without BV.
Treatment
- Metronidazole 500 mg PO BID × 7 days
Other topical regimens are available. Routine treatment of sexual partners is not generally recommended.
Vulvovaginal Candidiasis
Vulvovaginal candidiasis is most commonly caused by Candida albicans.
Like BV, vulvovaginal candidiasis is not considered an STI.
Presentation
Typical features include vulvar pruritus, vulvar erythema, external dysuria, dyspareunia and thick, white or “curdy” discharge.
Diagnosis
The diagnosis is often clinical in patients with a typical presentation. Microscopy or culture can be useful when the diagnosis is uncertain, symptoms are recurrent or complicated disease/non-albicans Candida is suspected.
Treatment
For uncomplicated vulvovaginal candidiasis:
Oral:
- Fluconazole 150 mg PO × 1
OR topical:
- An intravaginal azole such as clotrimazole or miconazole
Oral and topical azoles have similar efficacy for uncomplicated disease.
Pregnancy
During pregnancy, use a topical azole, generally for 7 days. Avoid routine oral fluconazole during pregnancy.
Routine treatment of asymptomatic sexual partners is not required.
The Bottom Line
STI management in the ED becomes much easier if you ask five questions:
1. What syndrome does this patient have?
Urethritis? Cervicitis? PID? Epididymitis? Proctitis? Genital ulcer disease? Vaginitis?
2. What organisms could cause it?
Don’t prematurely turn the syndrome into a microbiologic diagnosis.
3. What sites were exposed?
Genital? Pharyngeal? Rectal?
Test the anatomy that was exposed.
4. Do I need to treat now, or can I wait for the result?
That decision depends on the pre-test probability of infection, severity of illness, consequences of delayed treatment, potential harms of unnecessary treatment and reliability of follow-up.
5. What happens after the patient leaves?
Think about partner testing/treatment, HIV and syphilis testing, pregnancy, test of cure where indicated, repeat screening for reinfection and public health reporting.
The key is to remember that an STI test, like any diagnostic test, answers a specific question.
A negative urine NAAT does not tell you there is no pharyngeal or rectal infection.
A negative GC/CT test does not tell you there is no PID.
A negative early syphilis serology does not necessarily tell you there is no syphilis.
Start with the clinical context, determine the pre-test probability, order the test that actually answers your question, and then decide what the result means for the patient in front of you.
References
- Public Health Agency of Canada. Sexually transmitted and blood-borne infections: Guides for health professionals. Government of Canada. Updated 2026.
This is your overarching reference and landing page for the living Canadian STBBI guidelines.
PHAC STBBI Guides for Health Professionals - Public Health Agency of Canada. Genital herpes guide: Treatment and follow-up. Government of Canada.
Supports your first-episode and recurrent HSV regimens, indications for treatment, counselling and suppressive therapy. Current PHAC dosing is valacyclovir 1 g BID ×10 days for a first episode and either 500 mg BID ×3 days or 1 g daily ×3 days for recurrence.
PHAC Genital Herpes: Treatment and Follow-up - Public Health Agency of Canada. Syphilis guide: Treatment and follow-up. Government of Canada. Updated June 2026.
Supports benzathine penicillin dosing, staging-based treatment and serologic follow-up. PHAC explicitly places neurosyphilis treatment outside the scope of this particular guide.
PHAC Syphilis: Treatment and Follow-up - Public Health Ontario. Syphilis – Serology. Toronto: Ontario Agency for Health Protection and Promotion. Updated 2026.
This is the key Ontario-specific reference for your CMIA → RPR → ± TP-PA section. PHO confirms that CMIA detects treponemal IgG/IgM, RPR is the non-treponemal quantitative assay, TP-PA is used to adjudicate appropriate discordant results, and serology alone cannot stage infection.
Public Health Ontario Syphilis Serology - Public Health Agency of Canada. STI-associated syndromes guide: Anogenital ulcers. Government of Canada.
Supports your approach to genital ulcers, including HSV, syphilis and consideration of less common etiologies such as chancroid.
PHAC Anogenital Ulcers Guide - Centers for Disease Control and Prevention. Chancroid. Sexually Transmitted Infections Treatment Guidelines. Atlanta: CDC; 2021.
Useful specifically because PHAC does not provide a simple contemporary chancroid treatment table. CDC lists azithromycin 1 g PO once, ceftriaxone 250 mg IM once, ciprofloxacin 500 mg BID ×3 days, or erythromycin base 500 mg TID ×7 days.
CDC Chancroid Treatment Guidelines - Public Health Agency of Canada. STI-associated syndromes guide: Vaginitis. Government of Canada.
Supports the trichomoniasis section and the syndromic approach to vaginal discharge. It also clarifies that BV and VVC are not usually considered STIs and their treatment is outside the scope of the PHAC guide.
PHAC Vaginitis Guide - Public Health Agency of Canada. Gonorrhea guide: Key information and resources. Government of Canada. Updated June 2026.
Use this as the main reference for gonorrhea diagnosis, antimicrobial resistance, current treatment and follow-up. The current guidance incorporates the newer gonorrhea recommendations and June 2026 follow-up update.
PHAC Gonorrhea Guide - Public Health Agency of Canada, National Advisory Committee on Sexually Transmitted and Blood-Borne Infections. Interim guidance for the treatment of uncomplicated gonococcal infections. Government of Canada.
This is the particularly important reference supporting the ceftriaxone 500 mg IM once change and removal of routine azithromycin dual therapy. - Public Health Agency of Canada. Chlamydia and LGV guide: Treatment and follow-up. Government of Canada.
Supports doxycycline 100 mg BID ×7 days or azithromycin 1 g once for uncomplicated anogenital CT, doxycycline ×21 days for LGV, TOC indications and repeat screening at 3 months.
PHAC Chlamydia and LGV: Treatment and Follow-up - Public Health Agency of Canada. STI-associated syndromes guide: Proctitis. Government of Canada.
Supports your clinical presentation, exposure routes and diagnostic approach to sexually transmitted proctitis.
PHAC Proctitis Guide - Public Health Agency of Canada. STI-associated syndromes guide: Syndromic management. Government of Canada.
Useful as the overarching reference for urethritis, cervicitis, PID, epididymitis, proctitis and genital-ulcer syndromes. Importantly, its current table includes M. genitalium among organisms associated with proctitis.
PHAC STI Syndromic Management Guide - Public Health Agency of Canada. STI-associated syndromes guide: Pelvic inflammatory disease. Government of Canada. Updated June 2026.
Supports the clinical approach and current outpatient regimen of ceftriaxone 500 mg IM once + doxycycline 100 mg BID ×14 days + metronidazole 500 mg BID ×14 days.
PHAC Pelvic Inflammatory Disease Guide - Public Health Agency of Canada. STI-associated syndromes guide: Epididymitis. Government of Canada. Updated June 2026.
Supports the current ceftriaxone dose and the exposure-based approach to STI versus enteric pathogens.
PHAC Epididymitis Guide - Centers for Disease Control and Prevention. Bacterial Vaginosis. Sexually Transmitted Infections Treatment Guidelines. Atlanta: CDC; 2021.
This provides the treatment evidence PHAC deliberately leaves outside the scope of its STBBI guide, including metronidazole 500 mg PO BID ×7 days.
CDC Bacterial Vaginosis Guidelines - Centers for Disease Control and Prevention. Vulvovaginal Candidiasis. Sexually Transmitted Infections Treatment Guidelines. Atlanta: CDC; 2021.
Supports fluconazole 150 mg PO once or topical azole therapy for uncomplicated VVC, diagnostic testing for complicated/recurrent disease and longer treatment for severe/recurrent disease.
CDC Vulvovaginal Candidiasis Guidelines - Public Health Agency of Canada. STBBI prevention guide: STBBI management. Government of Canada.
Useful for your overall framework around testing, syndrome recognition, treatment, follow-up and partner management.
PHAC STBBI Management Guide
