Multisystem Processes & Disorders

Trichomoniasis and bacterial vaginosis

Clinical Overview and When to Suspect Trichomoniasis and Bacterial Vaginosis

— Any woman presenting with abnormal discharge, odor, dyspareunia, dysuria, or vulvar irritation

— Post-coital odor ("fishy after sex") → BV until proven otherwise

— Frothy yellow-green discharge + strawberry cervix → trichomoniasis

— Asymptomatic women being screened for other STIs (HIV, gonorrhea/chlamydia) — trichomoniasis is increasingly screened opportunistically

— BV is the most common cause of vaginitis in reproductive-age women in the US (~30%)

— Trichomoniasis is the most common non-viral curable STI worldwide, with rising recognition in women >40

— Both increase risk of HIV acquisition and transmission via mucosal inflammation

Board pearl: A Step 3 stem describing a woman with malodorous gray-white discharge after unprotected intercourse, without vulvar erythema or pruritus, is BV — not candidiasis. Pruritus and curd-like discharge point to yeast; frothy + cervical petechiae point to Trichomonas. Always test for concurrent gonorrhea, chlamydia, HIV, and syphilis when trichomoniasis is diagnosed — coinfection rates are high and screening is part of comprehensive STI care.

Bacterial vaginosis (BV) is a polymicrobial dysbiosis in which protective Lactobacillus species are replaced by anaerobes (Gardnerella vaginalis, Prevotella, Atopobium vaginae, Mobiluncus). It is not classically classified as an STI, but is strongly associated with sexual activity and partner change.

Trichomoniasis is caused by Trichomonas vaginalis, a flagellated protozoan, and is a sexually transmitted infection that is reportable in some jurisdictions and requires partner therapy.

Together, BV and trichomoniasis account for the majority of symptomatic vaginitis in adult women; candidiasis is the third leg of the differential.

When to suspect in primary care:

Epidemiology pearls:

Risk factors overlap: new/multiple partners, douching, IUD use (BV), Black race (disparity reflecting microbiome and access factors), smoking, and concurrent STIs.

Presentation Patterns and Key History

— Thin, homogeneous, gray-white discharge coating the vaginal walls

— Fishy odor, worse after intercourse or menses (alkaline semen/blood liberates amines)

— Minimal-to-no vulvar irritation, pruritus, or dyspareunia — this is a key distinguishing feature

— Up to 50–75% are asymptomatic; many diagnoses are incidental on Pap or STI screening

— Frothy, yellow-green, malodorous discharge

— Vulvar pruritus, burning, dyspareunia, dysuria (often mistaken for UTI)

— Postcoital bleeding from friable cervix

— Up to 70–85% of infected men and 50% of women are asymptomatic, fueling silent transmission

— Symptoms may worsen during/after menses

— Sexual history (5 P's): Partners (number, gender), Practices, Protection, Past STIs, Pregnancy intentions

— Timing relative to menses, intercourse, antibiotics, new soaps/douches

— Contraception (IUD, condoms), pregnancy status, LMP

— Prior episodes and treatment response — recurrence pattern matters

— Symptoms in partner(s); for trichomoniasis ask about urethritis symptoms in male partners

— Comorbid HIV, diabetes, immunosuppression

— Pregnancy — both conditions associated with preterm birth and PROM

— Pelvic/abdominal pain, fever, cervical motion tenderness → evaluate for PID, not simple vaginitis

— Postmenopausal bleeding with discharge → rule out atrophic vaginitis or malignancy

Key distinction: BV = odor without irritation; trichomoniasis = odor with irritation + dysuria; candidiasis = irritation without odor. This triad mnemonic answers a large fraction of vaginitis vignettes. Also remember: asymptomatic BV in a non-pregnant woman generally does not require treatment, but symptomatic disease and any trichomoniasis (symptomatic or not) always do.

Bacterial vaginosis classic presentation:

Trichomoniasis classic presentation:

Targeted history to obtain on the Step 3 CCS-style encounter:

Red-flag history that changes management:

Physical Exam Findings and Pelvic Assessment

— Inspect external genitalia for erythema, excoriation, lesions, condyloma

— Speculum exam with unlubricated speculum (lubricant alters pH testing) using warm water only

— Inspect vaginal walls and cervix; note discharge character, location, and adherence

— Bimanual exam to assess for cervical motion tenderness, adnexal tenderness, uterine tenderness — positive findings shift diagnosis toward PID

— Thin, gray-white, homogeneous discharge coating vaginal walls evenly

— No vulvar/vaginal erythema or edema — mucosa looks normal

— Vaginal pH > 4.5 (often 5.0–6.0)

— Positive whiff test: addition of 10% KOH releases fishy amine odor

— Frothy, yellow-green, purulent discharge with copious volume

— Vulvovaginal erythema and edema

— "Strawberry cervix" (colpitis macularis): punctate cervical hemorrhages — seen in <10% on naked-eye exam but highly specific when present

— Friable cervix bleeds easily on swabbing

— Vaginal pH > 4.5, often >5.0

— Whiff test may also be positive

— Curd-like white discharge with vulvar erythema/fissures, pH < 4.5 → candidiasis

— Mucopurulent cervicitis with friable cervix → consider gonorrhea/chlamydia coinfection

— CMT + fever + adnexal tenderness → PID; treat empirically and obtain NAAT

— Vulvar atrophy, thinned mucosa, pH > 5 in a postmenopausal woman → atrophic (genitourinary syndrome of menopause)

Step 3 management: A normal-appearing vulva with adherent gray discharge and an elevated pH on point-of-care testing supports BV and lets you start metronidazole on the same visit — you do not need to wait for NAAT. However, a friable cervix or strawberry appearance mandates NAAT for T. vaginalis, gonorrhea, chlamydia, plus HIV and syphilis serologies before treating, because empiric trichomoniasis therapy alone misses common coinfections.

General approach in the office:

Bacterial vaginosis exam findings:

Trichomoniasis exam findings:

Findings that should redirect you:

Diagnostic Workup — Initial Office Testing

— Vaginal pH using nitrazine paper applied to lateral wall (avoid cervical mucus, blood, semen — all falsely raise pH)

— Whiff (amine) test: 10% KOH on discharge → fishy odor = positive

— Saline wet mount microscopy: look for clue cells, motile trichomonads, WBCs

— KOH wet mount: look for pseudohyphae/budding yeast

1. Thin, homogeneous, white-gray discharge

2. Clue cells (squamous cells studded with adherent coccobacilli, obscuring borders) on saline wet mount — most specific

3. Vaginal pH > 4.5

4. Positive whiff test

— Motile, pear-shaped, flagellated trichomonads on saline prep — pathognomonic but sensitivity only ~50–60% and rapidly drops if slide cools/dries

— Increased PMNs (>10/hpf) supports inflammation

— NAAT for gonorrhea and chlamydia (vaginal swab acceptable, patient-collected OK)

— HIV and syphilis serologies in any new STI diagnosis

— Pregnancy test if relevant

— Consider hepatitis B/C, HPV/Pap per age if overdue

Board pearl: Clue cells = BV; motile trichomonads = trichomoniasis; pseudohyphae = Candida. Memorize the wet-mount triad cold. Also remember that Pap smear reporting of "Trichomonas" is reasonably specific but should be confirmed with NAAT before treating partners, while a Pap report of "shift in flora suggestive of BV" is not diagnostic — diagnose BV clinically with Amsel or Nugent, not by Pap.

Point-of-care vaginal fluid testing is the bedrock of vaginitis diagnosis and remains testable on Step 3:

Amsel criteria for BV — diagnosis requires 3 of 4:

Trichomoniasis on wet mount:

Nugent score (Gram stain): research/lab gold standard for BV; counts Lactobacillus, Gardnerella, and Mobiluncus morphotypes. Score 7–10 = BV. Rarely used in clinic but examinable.

Concurrent screening to obtain at the same visit:

Diagnostic Workup — Advanced and Confirmatory Studies

— Sensitivity 95–100% and specificity >95%, dramatically outperforming wet mount

— Approved on vaginal swabs (clinician- or patient-collected), endocervical swabs, and urine

— Available as part of multiplex panels with N. gonorrhoeae and C. trachomatis — efficient at the same visit

— Also FDA-cleared for male urine — use when treating male partners with persistent urethritis

— Point-of-care, results in 10–45 minutes

— Useful when microscopy is unavailable or low-yield

— Affirm VPIII detects Gardnerella, Candida, and Trichomonas simultaneously

— Detect ratios of Lactobacillus to BV-associated organisms

— High sensitivity/specificity vs Nugent

— Useful in recurrent or refractory BV where Amsel criteria are equivocal

— Recurrent BV (≥3 episodes in 12 months) → molecular panel, consider STI re-screen, evaluate for retained foreign body (forgotten tampon), assess douching/hygiene

— Persistent trichomoniasis after standard therapy → repeat NAAT 3 weeks later; if positive, culture with susceptibility and treat with high-dose tinidazole

— Always retest for trichomoniasis at 3 months after treatment — reinfection rates approach 20%

Key distinction: Wet mount is good enough to start empiric therapy in symptomatic women but is not adequate to rule out trichomoniasis when suspicion is high — order NAAT. For BV, clinical Amsel criteria remain standard; molecular panels are second-line for diagnostic uncertainty or recurrence and are not routinely needed in straightforward cases.

Nucleic acid amplification tests (NAAT) are now the preferred confirmatory test for Trichomonas vaginalis per CDC:

Rapid antigen and DNA hybridization tests (e.g., OSOM, Affirm VPIII):

Molecular BV panels (e.g., BD Max, Aptima BV):

Culture for T. vaginalis (Diamond's medium): historically the gold standard, now largely replaced by NAAT; reserve for suspected metronidazole resistance to allow susceptibility testing.

Indications to escalate diagnostics:

Risk Stratification and Management Logic

— Symptomatic BV → treat

— Asymptomatic BV in non-pregnant woman → do not routinely treat (exceptions: prior to gynecologic procedures such as IUD insertion, hysterectomy, endometrial biopsy, or abortion to reduce post-procedure infection)

— Any trichomoniasis (symptomatic or asymptomatic) → treat plus treat partners

— Pregnant women → see chunk 10

— HIV status: HIV-positive women with trichomoniasis require multi-dose metronidazole (500 mg BID × 7 days), not single-dose, due to higher treatment failure

— Pregnancy: associated with preterm birth, PROM, low birth weight, postpartum endometritis — symptomatic infection in pregnancy should be treated

— IUD users: BV may be more common; not an indication for IUD removal

— Recurrent BV (≥3/year): consider suppressive therapy with metronidazole gel twice weekly × 4–6 months

— USPSTF: insufficient evidence to screen asymptomatic pregnant women at low risk for preterm birth for BV; recommends against routine BV screening in asymptomatic pregnant women at low risk

— CDC: consider routine trichomoniasis screening in HIV-positive women annually and at entry to care

— Screen women at high STI risk (multiple partners, sex work, incarceration history)

— BV: partner treatment is not recommended

— Trichomoniasis: expedited partner therapy (EPT) with oral metronidazole/tinidazole where legally permitted; partners should also receive full STI evaluation

Step 3 management: When the question asks what to do with an asymptomatic non-pregnant woman with incidental BV on Pap, the answer is reassurance and no treatment. When the same finding is trichomoniasis on Pap, even if asymptomatic, treat her and her partner and screen for other STIs. This asymmetry — STI vs dysbiosis — is the conceptual core of the topic.

Decision framework once vaginitis is identified:

Risk stratification considerations:

Screening recommendations (USPSTF and CDC):

Partner management:

Pharmacotherapy — First-Line Regimens

— Metronidazole 500 mg PO BID × 7 days (preferred)

— Metronidazole 0.75% gel, one applicator (5 g) intravaginally daily × 5 days

— Clindamycin 2% cream, one applicator intravaginally at bedtime × 7 days (oil-based — weakens latex condoms/diaphragms × 5 days after use)

— Alternative: clindamycin 300 mg PO BID × 7 days, clindamycin ovules, secnidazole 2 g PO × 1, tinidazole 2 g PO daily × 2 days

— Women: Metronidazole 500 mg PO BID × 7 days (NEW preferred regimen — replaced single 2-g dose due to higher cure rates)

— Men: Metronidazole 2 g PO × 1 dose remains acceptable

— Alternative: Tinidazole 2 g PO × 1 (longer half-life, may have fewer GI side effects)

— HIV-positive women: always 7-day regimen

— Avoid alcohol during and for 24 h after metronidazole (72 h for tinidazole) — disulfiram-like reaction (flushing, vomiting, tachycardia). Recent evidence questions this, but boards still test it.

— Common side effects: metallic taste, nausea, headache, peripheral neuropathy with prolonged use

— Vaginal preparations: insert at bedtime; abstain or use backup contraception per regimen

— Complete full course; abstain from sex until both partners complete therapy and are asymptomatic (trichomoniasis)

— Re-induction with 7-day metronidazole, then metronidazole 0.75% gel twice weekly × 4–6 months as suppression

— Consider boric acid 600 mg vaginally daily × 21 days for refractory cases (off-label)

Board pearl: The biggest 2021 CDC change tested on Step 3: female trichomoniasis is now 7-day metronidazole, not single-dose. Single-dose 2-g is acceptable only for men and as an alternative when adherence is the limiting factor. Always counsel about alcohol avoidance — a classic Step 3 patient safety vignette.

Bacterial vaginosis — first-line options (CDC 2021):

Trichomoniasis — first-line (CDC 2021 update — important change!):

Counseling at prescription:

Recurrent BV regimen:

Treatment Failures, Resistance, and Expanded Pharmacology

— BV: persistent symptoms after completion of first-line therapy

— Trichomoniasis: positive NAAT or wet mount after directly observed therapy with reasonable adherence and no re-exposure

— Always re-screen for reinfection first — partner not treated, new partner, or non-adherence

— Confirm adherence and ask about alcohol use, vomiting, or missed doses

— Estimated 4–10% low-level resistance; high-level resistance rare

— Step-up regimen: tinidazole 2 g PO daily × 7 days, or metronidazole 2 g PO daily × 7 days

— Refractory cases: tinidazole 2–3 g PO + intravaginal tinidazole 500 mg BID × 14 days; consult ID

— Send for culture with susceptibility testing (CDC reference lab) when high-dose regimens fail

— Confirm diagnosis with Amsel or molecular panel

— Rule out reinfection sources: douching, retained foreign body, smoking

— Re-treat with extended course (10–14 days) of metronidazole

— Suppressive metronidazole gel twice weekly × 4–6 months after induction

— Adjunctive: boric acid 600 mg vaginal suppositories nightly × 21 days, then twice weekly

— Probiotics (oral or vaginal Lactobacillus): evidence limited but low-harm

— Topical clindamycin can cause pseudomembranous colitis — counsel on diarrhea reporting

— Tinidazole and metronidazole both pregnancy category B (metronidazole) and C (tinidazole) — see chunk 10

— Secnidazole is a single-dose oral granule formulation for BV, useful for adherence challenges

— No role for fluconazole, ceftriaxone, doxycycline in isolated BV or trichomoniasis — these treat candidiasis or coinfections respectively

CCS pearl: When managing recurrent BV in a CCS-style scenario, the order is: confirm diagnosis → treat the acute episode for 7 days → schedule follow-up at 1 month → if recurrence, initiate suppressive intravaginal metronidazole twice weekly. Document partner status and screen for STI coinfection at each step — this is exactly the longitudinal management voice Step 3 rewards.

Defining treatment failure:

Re-exposure vs true failure:

Metronidazole-resistant trichomoniasis:

Recurrent BV management ladder:

Special pharmacology pearls:

Special Populations — Elderly and Renal/Hepatic Impairment

— Vaginitis differential shifts: atrophic vaginitis (genitourinary syndrome of menopause) dominates due to estrogen deficiency

— Postmenopausal women still acquire BV and trichomoniasis, especially with new partners — do not dismiss STI risk

— Trichomoniasis in older women may be missed because of low clinical suspicion; NAAT-based screening recommended if symptomatic

— Always evaluate postmenopausal bleeding independently (endometrial biopsy, TVUS) — do not attribute to vaginitis without workup

— Thin, pale, friable mucosa with petechiae

— pH > 5 (loss of Lactobacillus)

— Scant discharge, dyspareunia, dysuria

— Treatment: vaginal estrogen (cream, ring, tablet) — first-line; not contraindicated in most breast cancer survivors but consult oncology

— Metronidazole: no dose adjustment for renal impairment in standard dosing; however, accumulation of metabolites in ESRD can occur — consider dose reduction with prolonged courses; give after hemodialysis (it is dialyzable)

— Tinidazole: supplement post-dialysis (one-time additional dose on dialysis days)

— Clindamycin: no renal adjustment needed

— Metronidazole and tinidazole are hepatically metabolized

— Reduce metronidazole dose by 50% in severe hepatic impairment (Child-Pugh C)

— Avoid tinidazole in severe hepatic dysfunction if alternatives exist

— Monitor for neurotoxicity (encephalopathy, peripheral neuropathy) with prolonged courses in cirrhotic patients

— Metronidazole potentiates warfarin — INR can rise dramatically; check INR within 3–5 days of starting, adjust warfarin

— Avoid with disulfiram (psychosis), lithium (toxicity), and busulfan

Board pearl: A postmenopausal woman on warfarin started on metronidazole for BV who presents with epistaxis and an INR of 7 is a classic Step 3 patient safety vignette. Always check INR within 3–5 days of starting metronidazole in any warfarin patient, or choose intravaginal clindamycin to minimize systemic exposure.

Postmenopausal women:

Atrophic vaginitis features that mimic infection:

Renal impairment:

Hepatic impairment:

Drug interactions relevant to older patients:

Pregnancy and Pediatric Considerations

— Associated with preterm birth, PROM, chorioamnionitis, postpartum endometritis, post-cesarean wound infection

— Symptomatic pregnant women: treat with oral metronidazole 500 mg BID × 7 days or clindamycin 300 mg PO BID × 7 days

— Intravaginal regimens are also acceptable in pregnancy

— USPSTF: recommends against routine screening of asymptomatic low-risk pregnant women; insufficient evidence for high-risk

— Metronidazole is safe in all trimesters per CDC and ACOG (older concerns about first-trimester teratogenicity not supported by current evidence)

— Associated with PROM, preterm delivery, low birth weight

— All symptomatic pregnant women should be treated

— Treatment: metronidazole 500 mg PO BID × 7 days (preferred); single-dose 2 g also acceptable

— Tinidazole is contraindicated in pregnancy (category C, limited safety data)

— Treating asymptomatic trichomoniasis in pregnancy is still recommended by CDC, even though it has not been shown to reduce preterm birth, because of symptom relief and transmission prevention

— Safe in breastfeeding: with single-dose 2-g metronidazole, withhold breastfeeding for 12–24 hours; with 7-day regimen, continue breastfeeding (low infant exposure)

— Rare; can cause neonatal vaginal discharge or respiratory infection from intrapartum transmission

— Treat with metronidazole (consult pediatrics)

— Confidentiality laws permit minors to consent to STI testing/treatment in all 50 states

— Screen sexually active adolescent girls for chlamydia/gonorrhea annually; add trichomoniasis NAAT if symptomatic or high-risk

— Vaginitis in prepubertal girls is most often non-specific or due to Streptococcus, Shigella, or pinworm — trichomoniasis in a young child raises strong concern for sexual abuse and mandates reporting

Step 3 management: A pregnant woman with symptomatic BV at 22 weeks receives oral metronidazole 500 mg BID × 7 days — do not withhold treatment due to outdated teratogenicity concerns. A prepubertal girl with confirmed trichomoniasis triggers mandatory child protective services reporting and a forensic evaluation; do not simply prescribe metronidazole and discharge.

BV in pregnancy:

Trichomoniasis in pregnancy:

Neonatal trichomoniasis:

Adolescents:

Complications and Adverse Outcomes

— Preterm premature rupture of membranes (PPROM)

— Preterm labor and delivery

— Low birth weight

— Chorioamnionitis

— Postpartum endometritis

— Post-cesarean wound infection

— Spontaneous abortion (BV)

— Post-procedure infection after hysterectomy, abortion, endometrial biopsy, IUD insertion — preoperative treatment of BV reduces this risk

— Increased risk of PID, though BV alone is not a typical PID pathogen

— Increased susceptibility to HIV, HSV-2, HPV, gonorrhea, chlamydia acquisition

— Increased HIV acquisition and transmission (2–3× risk; biological plausibility = mucosal inflammation, recruitment of CD4 cells)

— Cervical neoplasia association (modest)

— In men: urethritis, prostatitis, epididymitis, infertility (rare)

— Tubal infertility: possible association in women

— Disulfiram-like reaction with alcohol + metronidazole/tinidazole

— Peripheral neuropathy and CNS toxicity (encephalopathy, seizures, cerebellar dysfunction) with prolonged metronidazole — typically reversible

— Pseudomembranous colitis from clindamycin

— Vulvovaginal candidiasis after antibiotic therapy — counsel patients

— Drug interactions: metronidazole + warfarin (bleeding), metronidazole + lithium (toxicity)

— BV recurs in >50% within 12 months even after appropriate treatment

— Trichomoniasis reinfection rate ~17% at 3 months — hence the 3-month retest recommendation

Key distinction: BV's most clinically impactful complications are obstetric and post-procedural, while trichomoniasis's most impactful complication is enhanced HIV transmission. Both contribute to a pro-inflammatory genital tract environment, and both are independently associated with adverse pregnancy outcomes — which is why symptomatic infection should always be treated in pregnancy regardless of risk stratification.

Obstetric complications (both BV and trichomoniasis):

Gynecologic complications of BV:

Complications of trichomoniasis:

Treatment-related complications:

Recurrence:

When to Escalate Care and Consult

— Recurrent BV despite suppressive therapy

— Persistent trichomoniasis despite high-dose tinidazole — for culture, susceptibility testing, and tailored regimens

— Diagnostic uncertainty after standard workup

— Pregnant women with PPROM or preterm labor and concurrent vaginitis — co-manage with OB

— Pelvic pain + fever + CMT → suspected PID; treat empirically with CDC PID regimen (ceftriaxone + doxycycline ± metronidazole), consider inpatient if pregnant, severe illness, tubo-ovarian abscess, or unable to tolerate oral therapy

— Tubo-ovarian abscess on imaging → admit, IV antibiotics, possible drainage

— Septic abortion → emergent OB consultation

— Toxic shock-like presentation with retained foreign body → ED transfer

— Trichomoniasis is reportable in some jurisdictions

— All new STI diagnoses warrant expedited partner therapy consideration where legal

— HIV-positive women with trichomoniasis: coordinate with HIV care team

— Sepsis from ascending infection

— Severe drug reaction (Stevens-Johnson, severe colitis)

— Pregnant women with chorioamnionitis or preterm labor

— Social work involvement for suspected abuse, intimate partner violence disclosed during sexual history, or pediatric STI

— Pharmacy consult for metronidazole interactions in polypharmacy patients

CCS pearl: In a CCS-style case where you initially diagnosed BV but the patient returns 5 days later with fever, RLQ pain, and CMT, stop the BV pathway and pivot to PID workup: CBC, CRP, HCG, NAAT, transvaginal ultrasound, and empiric CDC PID regimen. Document the reassessment and escalation clearly — Step 3 rewards recognizing when a working diagnosis no longer fits.

Vaginitis is overwhelmingly an outpatient diagnosis, but several scenarios require escalation:

Refer to gynecology/ID when:

Emergency/urgent referral if:

Public health and infectious disease coordination:

Inpatient triage criteria (uncommon for isolated vaginitis):

Multidisciplinary considerations:

Key Differentials — Other Causes of Vaginitis

— Thick, curd-like white discharge; no odor

— Vulvar pruritus, erythema, edema, fissures, dyspareunia, dysuria

— pH < 4.5 (normal vaginal pH preserved)

— Pseudohyphae and budding yeast on KOH wet mount

— Treatment: fluconazole 150 mg PO × 1 (uncomplicated) or topical azoles (clotrimazole, miconazole)

— Complicated VVC (recurrent, severe, non-albicans, immunocompromised): fluconazole 150 mg every 72 h × 3 doses; recurrent: suppressive weekly fluconazole × 6 months

— Inflammation from aerobic organisms (E. coli, Staph aureus, group B strep, enterococci)

— Yellow discharge, vulvovaginal burning, elevated pH

— Less well-defined entity; treat based on culture

— Purulent discharge, dyspareunia, elevated pH

— Wet mount: PMNs, parabasal cells, elevated pH, but no clue cells or trichomonads

— Treatment: intravaginal clindamycin or hydrocortisone

— Excess Lactobacillus → cytolysis of epithelium → burning, dyspareunia

— pH < 4.5; treatment: sodium bicarbonate douches (paradoxical case where alkalinization helps)

— Postmenopausal; thin pale mucosa, dyspareunia, pH > 5

— Treatment: vaginal estrogen

— New soaps, douches, spermicides, lubricants

— Erythema and pruritus without infection; remove offending agent

Key distinction: The fastest discriminator at the bedside is the pH + wet mount combination: pH < 4.5 + pseudohyphae = candida; pH > 4.5 + clue cells = BV; pH > 4.5 + motile trichomonads = trichomoniasis; pH > 5 + parabasal cells, no organisms = atrophic or DIV. Memorize this matrix — Step 3 vignettes embed these data points and expect the answer in one click.

Vulvovaginal candidiasis (VVC):

Aerobic vaginitis:

Desquamative inflammatory vaginitis (DIV):

Cytolytic vaginosis:

Atrophic vaginitis (GSM):

Allergic/irritant contact vaginitis:

Key Differentials — Beyond Vaginitis

— Gonorrhea, chlamydia, HSV, Mycoplasma genitalium as primary causes

— Mucopurulent endocervical discharge, friable cervix, contact bleeding

— Treat empirically: ceftriaxone 500 mg IM × 1 + doxycycline 100 mg BID × 7 days for gonorrhea/chlamydia coverage pending NAAT

— Often coexists with trichomoniasis — always co-screen

— Lower abdominal pain, CMT, uterine or adnexal tenderness

— Fever, leukocytosis variable

— CDC outpatient regimen: ceftriaxone 500 mg IM + doxycycline 100 mg PO BID × 14 days + metronidazole 500 mg PO BID × 14 days

— Hospitalize for pregnancy, severe illness, tubo-ovarian abscess, inability to tolerate orals, failure of outpatient therapy

— Dysuria, frequency, urgency — can overlap with trichomoniasis symptoms

— Urinalysis: pyuria, nitrites, bacteriuria

— Always consider concurrent vaginitis when dysuria is "external" rather than internal

— Painful vesicles/ulcers, prodrome, inguinal lymphadenopathy

— PCR/culture of lesion fluid; serology for type-specific antibodies

— Treat with acyclovir, valacyclovir, or famciclovir

— Profuse foul discharge in adults; foul discharge in children

— Speculum exam diagnostic and therapeutic — remove and lavage

— Lichen sclerosus (atrophic white plaques, postmenopausal), lichen planus, contact dermatitis

— Biopsy if suspected; refer to gyn/derm

— Cervical or endometrial cancer can present with bloody/malodorous discharge — Pap, biopsy, and TVUS as indicated

Board pearl: "External dysuria" (burning as urine touches inflamed vulva) suggests vulvovaginitis (trichomoniasis, candida, herpes); "internal dysuria" (burning along urethra) suggests UTI or urethritis (chlamydia, gonorrhea). A patient with both should be evaluated for both — order urinalysis, urine NAAT for GC/CT, and vaginal swab for trichomoniasis and BV rather than treating empirically for cystitis alone.

Cervicitis:

Pelvic inflammatory disease (PID):

Urinary tract infection:

HSV genital infection:

Foreign body (retained tampon, condom):

Vulvar dermatoses:

Malignancy:

Secondary Prevention and Long-Term Plan

— Adherence: complete full course even if symptoms resolve early

— Sexual abstinence until both partners complete therapy (trichomoniasis) or 1 week (BV) — pragmatic recommendation

— Condom use consistently and correctly — reduces BV recurrence and STI transmission

— Avoid douching — disrupts vaginal flora and is associated with BV, PID, ectopic pregnancy

— Avoid unnecessary vaginal products (scented soaps, sprays)

— Treat all sexual partners from the past 60 days; expedited partner therapy (EPT) where legal

— Retest at 3 months in all sexually active women — reinfection rate ~17%

— Screen HIV-positive women annually

— Full STI panel at diagnosis and at follow-up: HIV, syphilis, gonorrhea, chlamydia, hepatitis B/C

— Update HPV vaccination if age-eligible (now through age 26, shared decision through 45)

— No partner treatment indicated

— For recurrent BV: suppressive intravaginal metronidazole gel twice weekly × 4–6 months

— Consider vaginal probiotics containing L. crispatus (evidence emerging)

— Smoking cessation — smoking disrupts vaginal microbiome

— Pap smear per age guidelines (21–65, every 3 years cytology or every 5 years co-test 30–65)

— Contraception counseling; LARC if desired

— Vaccinations: HPV, hepatitis B, MMR/varicella if non-immune, Tdap

— Intimate partner violence screening

— Depression screening (PHQ-2)

Step 3 management: The treatment visit is also a comprehensive preventive medicine encounter — Step 3 rewards bundling. After diagnosing trichomoniasis, the model answer adds: HIV/syphilis testing, partner notification, condom counseling, HPV vaccine if eligible, Pap if due, and a 3-month retest appointment. Missing the 3-month retest is a common wrong-answer trap.

Counseling at treatment completion (every patient):

Trichomoniasis-specific secondary prevention:

BV-specific secondary prevention:

Health maintenance to address at the same visit:

Follow-Up, Monitoring, and Counseling

— BV, uncomplicated: no test of cure if symptoms resolve; return if symptoms recur

— BV, recurrent: follow-up at 1 month after induction; reassess every 3 months during suppression

— Trichomoniasis: retest at 3 months with NAAT regardless of symptoms (reinfection screening); earlier if persistent symptoms

— HIV-positive women: annual trichomoniasis screening

— Pregnancy: reassess at next prenatal visit; consider test of cure 3–4 weeks after treatment for symptomatic infections

— Symptom resolution within 7 days

— Side effect tolerance — GI upset, metallic taste, headache

— INR if on warfarin (check within 3–5 days)

— Adherence assessment

— Mechanism explanation: BV = imbalance, not infection from partner; trichomoniasis = sexually transmitted parasitic infection

— Recurrence is common — does not necessarily mean reinfection or partner infidelity (especially for BV)

— Asymptomatic transmission of trichomoniasis is common — emphasize partner therapy

— Alcohol avoidance with metronidazole/tinidazole

— Reproductive health: pregnancy planning, fertility implications

— Mental health: STI diagnosis can be emotionally distressing; offer support and address shame/stigma

— Document partner notification efforts, EPT prescriptions, refusal of testing if applicable

— Document allergies and prior treatment failures

— Document counseling on alcohol, sexual practices, follow-up plan

— CDC patient handouts, plain-language materials, professionally translated for non-English speakers

— Reliable websites: cdc.gov, acog.org, plannedparenthood.org

CCS pearl: Scheduling the 3-month NAAT retest for trichomoniasis is one of the highest-yield "advance the clock" actions Step 3 will reward. Pair it with partner therapy verification, condom counseling, and screening for repeat STIs to capture full credit on a longitudinal management vignette.

Follow-up cadence:

Monitoring parameters during/after therapy:

Counseling content (deliver explicitly):

Documentation:

Patient education resources:

Ethical, Legal, and Patient Safety Considerations

— All 50 US states allow minors to consent to STI testing and treatment without parental consent

— Document confidentiality decisions; avoid billing to parental insurance when feasible (consider title X clinics, confidential billing pathways)

— Adolescent vignettes on Step 3 frequently test this: do not require parental consent for STI care

— Trichomoniasis in a prepubertal child → strongly suggests sexual abuse; report to child protective services and coordinate forensic exam

— Suspected intimate partner violence disclosed during sexual history → assess safety, provide resources; direct reporting requirements vary by state (mandated in some)

— Reportable STIs vary by jurisdiction — know that gonorrhea, chlamydia, syphilis, HIV are always reportable; trichomoniasis is reportable in some states

— Legally permitted in most US states for gonorrhea, chlamydia, and trichomoniasis in many jurisdictions

— Provide prescription or medication for the partner without examining them — counsel partner about potential side effects via patient

— Document EPT prescription clearly

— Treating a pregnant patient with metronidazole: explicitly discuss the safety data and the risks of untreated infection — historical concern about teratogenicity is not supported; document shared decision-making

— Counsel on alcohol-metronidazole interaction — a documented Joint Commission patient safety topic

— Hand off pending NAAT results explicitly to the patient and clearly to the next provider

— Telehealth-prescribed therapy: ensure follow-up testing pathway is established before sign-off

— Warfarin interaction: communicate to anticoagulation clinic when starting metronidazole — a recognized transition-of-care error

Board pearl: A 13-year-old presents alone requesting STI testing. The correct action is to provide confidential testing and treatment without requiring parental notification. Conversely, a 4-year-old with trichomoniasis is a sentinel event requiring CPS report and forensic evaluation. The line between "respecting autonomy" and "mandatory reporting" hinges on age and developmental capacity, not on parental preference.

Minor consent and confidentiality:

Mandatory reporting:

Expedited partner therapy (EPT):

Informed consent edge cases:

Transition-of-care safety:

High-Yield Associations and Rapid-Fire Clinical Facts

Board pearl: If a Step 3 stem mentions a recent CDC guideline change, the trichomoniasis 7-day regimen for women is the highest-yield update to anchor in memory — it has appeared on board-style questions repeatedly since 2021.

BV organisms: Gardnerella vaginalis, Prevotella, Atopobium vaginae, Mobiluncus, Mycoplasma hominis — polymicrobial dysbiosis with loss of hydrogen-peroxide-producing Lactobacillus

Trichomonas vaginalis: flagellated protozoan; only the trophozoite form, no cyst form; transmits through direct genital contact

Amsel criteria (need 3 of 4): thin homogeneous discharge, clue cells, pH >4.5, positive whiff

Clue cells: vaginal epithelial cells coated with adherent bacteria, obscuring cell borders — pathognomonic for BV

Strawberry cervix: punctate cervical hemorrhages — specific (when present) for trichomoniasis; sensitivity only 2–5% on naked eye, ~45% on colposcopy

Wet mount pH cheat sheet: normal <4.5; candida <4.5; BV/trich/atrophic >4.5

CDC 2021 update: female trichomoniasis = 7-day metronidazole, not single 2-g dose

HIV-positive women with trichomoniasis: always 7-day regimen

Metronidazole + alcohol = disulfiram-like reaction (avoid 24 h after; 72 h with tinidazole)

Metronidazole + warfarin = elevated INR; + lithium = lithium toxicity

Topical clindamycin weakens latex condoms × 5 days

Tinidazole: contraindicated in pregnancy

Metronidazole: safe in all trimesters of pregnancy and during breastfeeding (with brief interruption after 2-g dose)

No partner treatment for BV; always partner treatment for trichomoniasis

Retest for trichomoniasis at 3 months — reinfection prevalence ~17%

Asymptomatic BV in non-pregnant women → no treatment unless preprocedural

Asymptomatic trichomoniasis → always treat

Recurrent BV suppression: metronidazole gel twice weekly × 4–6 months

BV increases HIV acquisition; trichomoniasis increases HIV acquisition and transmission

Trichomoniasis in prepubertal child = sexual abuse until proven otherwise → report

Pap report of "trichomonads" has moderate specificity; confirm with NAAT before treating partners; Pap report of "shift in flora" is not diagnostic for BV

Secnidazole 2 g PO × 1 — single-dose BV option for adherence challenges

EPT legal for trichomoniasis in many states

Board Question Stem Patterns

— 28-year-old G1P1 with malodorous gray discharge worse after intercourse, no pruritus. Wet mount shows clue cells, pH 5.0, positive whiff. Answer: oral metronidazole 500 mg BID × 7 days. Distractors: fluconazole, ceftriaxone, no treatment.

— 32-year-old with frothy yellow-green discharge, dyspareunia, strawberry cervix. Wet mount shows motile flagellated organisms. Answer: metronidazole 500 mg BID × 7 days for patient AND partner. Test for HIV, syphilis, gonorrhea, chlamydia.

— 22-week pregnant woman with BV symptoms. Answer: oral metronidazole 500 mg BID × 7 days. Distractors: defer until postpartum, single-dose 2 g.

— Patient on metronidazole drinks wine, develops flushing/vomiting. Answer: disulfiram-like reaction; supportive care.

— Pap reports "shift in flora consistent with BV" in asymptomatic non-pregnant woman. Answer: no treatment, reassurance.

— Same scenario but Pap shows trichomonads. Answer: confirm with NAAT, treat patient and partner.

— Answer: metronidazole 500 mg BID × 7 days (not single dose). Annual screening recommended.

— Patient on warfarin started metronidazole, presents with epistaxis and INR 7. Answer: hold warfarin, vitamin K if severe, recognize metronidazole-warfarin interaction.

— 5-year-old with vaginal discharge, NAAT positive for trichomoniasis. Answer: report to CPS, forensic exam, treat with metronidazole.

— Woman with 4 episodes in 1 year. Answer: induction metronidazole 7 days + suppressive gel twice weekly × 4–6 months.

— Confirmed reinfection ruled out. Answer: tinidazole 2 g PO daily × 7 days; if still failing, ID consult and culture susceptibility.

— 15-year-old requests STI testing without parents knowing. Answer: provide confidential care; do not require parental consent.

Step 3 management: These stems repeat across exam cycles with minor numerical and demographic variations — recognizing the archetype is faster than re-deriving the answer.

Stem 1 — Classic BV vignette:

Stem 2 — Classic trichomoniasis vignette:

Stem 3 — Pregnancy:

Stem 4 — Alcohol interaction:

Stem 5 — Asymptomatic Pap finding:

Stem 6 — Asymptomatic trichomoniasis on Pap:

Stem 7 — HIV-positive woman with trichomoniasis:

Stem 8 — Warfarin interaction:

Stem 9 — Prepubertal trichomoniasis:

Stem 10 — Recurrent BV:

Stem 11 — Refractory trichomoniasis after first-line:

Stem 12 — Adolescent confidentiality:

One-Line Recap

Bacterial vaginosis is a polymicrobial dysbiosis treated with metronidazole only when symptomatic (or before gynecologic procedures or in pregnancy), while trichomoniasis is a sexually transmitted protozoal infection that is always treated — now with a 7-day metronidazole regimen in women per the 2021 CDC update — along with partner therapy, comprehensive STI screening, and a 3-month retest for reinfection.

Board pearl: When a Step 3 question gives you discharge character + pH + wet mount finding, the diagnosis is one click away — and the next click is recognizing whether partner therapy, retest scheduling, pregnancy adjustments, or coinfection screening drives the management answer.

Three-condition vaginitis matrix: BV = clue cells, pH >4.5, no inflammation, gray discharge; Trichomoniasis = motile flagellates, pH >4.5, strawberry cervix, frothy yellow-green discharge; Candidiasis = pseudohyphae, pH <4.5, curd-like discharge, pruritus.

Treatment essentials: BV → metronidazole 500 mg BID × 7 days (oral) or 0.75% gel × 5 days; clindamycin alternative. Trichomoniasis → metronidazole 500 mg BID × 7 days in women (NEW), 2 g single dose acceptable in men, plus treat all partners and screen for full STI panel including HIV.

Special populations: Pregnant women with symptomatic BV or trichomoniasis → oral metronidazole 500 mg BID × 7 days (safe in all trimesters); HIV-positive women → 7-day regimen always; postmenopausal women → consider atrophic vaginitis and treat with vaginal estrogen; prepubertal trichomoniasis → mandatory CPS report; adolescents → confidential STI care without parental consent.

Counseling and follow-up: Avoid alcohol with metronidazole (24 h) and tinidazole (72 h); check INR with warfarin; counsel against douching; condom use reduces recurrence and STI co-acquisition; 3-month retest for all treated trichomoniasis; suppressive intravaginal metronidazole for recurrent BV.