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STI in Microbiology - Clinical & Exam-Based Quiz 🧫

Here are 25 questions spanning vignette-based, single-best-answer, and recall formats - modeled on USMLE, MBBS, NEET-PG, and MRCP/MRCS patterns. Scroll down to see answers with explanations.

SECTION 1: SYPHILIS

Q1. A 28-year-old man presents with a painless indurated ulcer on his glans penis that appeared 3 weeks ago. He has no other symptoms. Serology: VDRL reactive 1:8. What is the stage of syphilis, and what is the first-line treatment?

A. Secondary syphilis - Doxycycline B. Primary syphilis - Benzathine penicillin G 2.4 MU IM single dose C. Primary syphilis - Azithromycin 1g oral D. Latent syphilis - Benzathine penicillin G 2.4 MU IM x3 doses

Q2. A 32-year-old woman has a diffuse maculopapular rash involving her palms and soles, generalized painless lymphadenopathy, and condylomata lata around the perineum. RPR is reactive 1:128. Which statement about this stage is TRUE?

A. The lesions resolve only with treatment B. CSF abnormalities are detectable in up to 40% of patients at this stage C. She is no longer infectious D. Penicillin allergy is an absolute contraindication to treatment

Q3. A 55-year-old man with untreated syphilis from 25 years ago presents with wide-based gait, loss of deep pain sensation, and areflexia. His pupils react to accommodation but NOT to light. Diagnosis?

A. General paresis B. Meningovascular syphilis C. Tabes dorsalis D. Gummatous syphilis

Q4. A 40-year-old male with HIV (CD4 180 cells/uL) has RPR 1:64 but no neurological symptoms. Lumbar puncture reveals CSF VDRL reactive. What is the most appropriate management?

A. Benzathine penicillin G 2.4 MU IM x1 dose B. Aqueous crystalline penicillin G IV for 10-14 days C. Doxycycline 100 mg BD for 28 days D. Observation; treat only if symptomatic

Q5. The Jarisch-Herxheimer reaction occurs within hours of treating early syphilis. Which of the following best describes its pathophysiology?

A. IgE-mediated penicillin allergy B. Antigen-antibody complex deposition in vessels C. Release of cytokines (TNF-α, IL-6) from mass treponeme lysis D. Serum sickness from repeated penicillin doses

SECTION 2: GONORRHEA

Q6. A 22-year-old male presents with purulent urethral discharge and dysuria. Gram stain of urethral exudate shows polymorphonuclear cells with intracellular gram-negative diplococci. Which organism is responsible, and what is the appropriate treatment?

A. Chlamydia trachomatis - Doxycycline B. Neisseria gonorrhoeae - Ceftriaxone 500 mg IM single dose C. Mycoplasma genitalium - Azithromycin 1g D. Haemophilus ducreyi - Azithromycin

Q7. A 19-year-old woman presents with mucopurulent cervical discharge and pelvic tenderness. Endocervical swab PCR is positive for N. gonorrhoeae. Which additional co-infection must ALWAYS be tested for simultaneously?

A. Trichomonas vaginalis only B. Chlamydia trachomatis, syphilis, and HIV C. HSV-2 and HPV D. Bacterial vaginosis

Q8. Which of the following is NOT a typical feature of disseminated gonococcal infection (DGI)?

A. Asymmetric migratory polyarthralgia B. Purulent monoarthritis of the knee C. Painless papulovesicular skin lesions on the extremities D. Painful indurated inguinal ulcer

Q9. Regarding N. gonorrhoeae - which is correct about antibiotic resistance?

A. It remains universally susceptible to penicillin B. Quinolone resistance is now widespread globally, making fluoroquinolones first-line C. Extended-spectrum cephalosporins (ceftriaxone) remain the backbone of treatment due to widespread resistance to penicillins and fluoroquinolones D. Resistance has no impact on treatment choice

SECTION 3: CHLAMYDIA

Q10. A 24-year-old woman is screened for STIs. She is asymptomatic. Urine NAAT returns positive for C. trachomatis (serovars D-K). What is the recommended treatment and follow-up?

A. Doxycycline 100 mg BD for 7 days; no test of cure needed B. Azithromycin 1g single dose; routine test of cure advised C. Ceftriaxone 500 mg IM; re-test in 2 weeks D. Ciprofloxacin 500 mg BD for 5 days

Q11. Which serovars of C. trachomatis cause lymphogranuloma venereum (LGV)?

A. A, B, C B. D through K C. L1, L2, L3 D. All serovars equally

Q12. A 30-year-old MSM (men who sex with men) presents with painful anorectal discharge, tenesmus, and inguinal lymphadenopathy. PCR of rectal swab confirms C. trachomatis L2. Which is the most appropriate treatment?

A. Doxycycline 100 mg BD for 21 days B. Azithromycin 1g single dose C. Benzathine penicillin G 2.4 MU IM D. Erythromycin 500 mg QID for 7 days

Q13. A 3-week-old neonate develops bilateral conjunctivitis with mucopurulent discharge. The mother was known to have untreated C. trachomatis infection during pregnancy. What is the diagnosis, and what other complication should be screened for?

A. Neonatal gonococcal ophthalmia; no further workup needed B. Neonatal chlamydial ophthalmia; screen for chlamydial pneumonia (onset 2-12 weeks) C. Chemical conjunctivitis from silver nitrate; treat with saline irrigation D. Herpes simplex keratoconjunctivitis; treat with topical acyclovir

SECTION 4: GENITAL ULCERS - DIFFERENTIAL DIAGNOSIS

Q14. Match each pathogen to its classical ulcer description:

Pathogen	Ulcer Feature
HSV-2	?
T. pallidum (syphilis)	?
H. ducreyi (chancroid)	?
C. trachomatis L1-L3 (LGV)	?

Which combination is CORRECT?

A. HSV-2 = painless indurated; Syphilis = painful vesicular; Chancroid = painful with undermined edges; LGV = painless B. HSV-2 = multiple painful superficial vesicular/ulcers; Syphilis = single painless indurated; Chancroid = painful with undermined edges; LGV = small transient ulcer then inguinal bubo C. HSV-2 = single painless firm; Syphilis = multiple painful; Chancroid = painless; LGV = painful crusted D. All four are painless and indurated

Q15. In a resource-limited country, a 28-year-old man presents with a painful genital ulcer with ragged undermined edges, and a tender fluctuant inguinal lymph node (bubo). Gram stain shows "school of fish" pattern. Diagnosis?

A. Primary syphilis B. Granuloma inguinale (donovanosis) C. Chancroid - Haemophilus ducreyi D. LGV

Q16. Donovanosis (granuloma inguinale) is caused by which organism, and what is its histologic hallmark?

A. Haemophilus ducreyi - school of fish pattern on Gram stain B. Klebsiella granulomatis (formerly Calymmatobacterium granulomatis) - Donovan bodies in macrophages on Wright/Giemsa stain C. Treponema pallidum - darkfield microscopy D. C. trachomatis L2 - intracytoplasmic inclusions on Giemsa

SECTION 5: HERPES & VIRAL STIs

Q17. A 26-year-old woman has recurrent painful vesicular eruptions on the vulva every 6 weeks. She tests positive for HSV-2 IgG. She is now pregnant at 34 weeks. Which management is most appropriate?

A. No treatment needed; HSV-2 does not affect the fetus B. Acyclovir suppressive therapy from 36 weeks to prevent neonatal HSV at delivery C. Cesarean section regardless of lesion activity D. Valacyclovir only after delivery

Q18. Which statement about HSV vs. syphilis ulcer is MOST useful in clinical differentiation?

A. Syphilis ulcers are multiple and painful; HSV is single and painless B. Syphilis (primary chancre) is single, firm, and painless with indurated borders; HSV ulcers are multiple, painful, and superficial with erythematous bases C. Both are managed with acyclovir D. Only syphilis responds to penicillin; HSV does not respond to any antiviral

SECTION 6: TRICHOMONAS & BV

Q19. A 25-year-old woman presents with profuse frothy yellow-green vaginal discharge, vulvar pruritus, and a "strawberry cervix" on examination. Wet mount shows motile pear-shaped flagellated organisms. What is the treatment?

A. Metronidazole 500 mg BD for 7 days (or 2g single dose) for patient AND partner B. Clindamycin vaginal cream for 7 days C. Fluconazole 150 mg single oral dose D. Doxycycline 100 mg BD for 7 days

Q20. A 22-year-old woman with recurrent vaginal discharge has a pH of 5.5, positive whiff test (fishy odor with KOH), and clue cells on wet mount. Diagnosis and treatment?

A. Vulvovaginal candidiasis - fluconazole B. Trichomoniasis - metronidazole + treat partner C. Bacterial vaginosis - metronidazole 500 mg BD 7 days (or clindamycin) D. Atrophic vaginitis - topical estrogen

SECTION 7: HPV & PID

Q21. Which HPV strains are responsible for genital warts (condylomata acuminata), and which are high-risk for cervical cancer?

A. HPV 6 and 11 for warts; HPV 16 and 18 for cervical cancer B. HPV 16 and 18 for warts; HPV 6 and 11 for cancer C. HPV 31 and 33 for warts; HPV 6 and 11 for cancer D. All HPV strains carry equal cancer risk

Q22. A 23-year-old woman presents with lower abdominal pain, fever (38.4°C), cervical motion tenderness, and mucopurulent cervical discharge. Laparoscopy would show perihepatic adhesions ("violin string" adhesions). What syndrome is this, and which organisms are responsible?

A. Appendicitis - E. coli B. Fitz-Hugh-Curtis syndrome - N. gonorrhoeae and/or C. trachomatis C. Ovarian torsion - no infectious cause D. Tubo-ovarian abscess - Bacteroides fragilis alone

Q23. Which sequelae are associated with untreated PID (pelvic inflammatory disease)? Select the BEST answer.

A. Infertility from tubal occlusion, ectopic pregnancy, and chronic pelvic pain B. Cervical cancer and ovarian torsion C. Hepatitis C and cirrhosis D. No long-term sequelae if initially asymptomatic

SECTION 8: DIAGNOSTIC TESTS

Q24. Order the following syphilis serology tests correctly:

RPR / VDRL - nontreponemal test
TPHA / FTA-ABS - treponemal test

Which statement is TRUE?

A. Nontreponemal tests (RPR/VDRL) remain positive for life and are used for screening; treponemal tests (FTA-ABS) are used to monitor treatment response B. Treponemal tests (FTA-ABS/TPHA) remain positive for life even after successful treatment; nontreponemal tests (RPR/VDRL) decline with treatment and are used to monitor response C. Both test types decline to zero after treatment D. Only darkfield microscopy is diagnostic for syphilis

Q25. A 28-year-old asymptomatic woman attends a GUM clinic. She has a reactive RPR 1:4 but negative FTA-ABS. Interpretation?

A. Active syphilis - treat immediately B. Biologic false positive RPR; treponemal test negative confirms no syphilis C. Latent syphilis - treat with benzathine penicillin x3 doses D. Primary syphilis - treat with benzathine penicillin x1 dose

ANSWERS & EXPLANATIONS

A1. B - Painless indurated ulcer = primary syphilis chancre (incubation ~21 days). First-line is benzathine penicillin G 2.4 MU IM single dose. Azithromycin has emerging resistance data; doxycycline is penicillin-allergy alternative. (Harrison's 22e, p.1473)

A2. B - Secondary syphilis features: palmar/plantar rash, condylomata lata, generalized lymphadenopathy. CSF abnormalities occur in up to 40% even without neurologic symptoms. Lesions resolve spontaneously (NOT only with treatment). Penicillin-allergic pregnant patients must be desensitized. (Harrison's 22e)

A3. C - Tabes dorsalis - onset 25-30 years post-infection; posterior column demyelination causes ataxia, areflexia, loss of deep pain/temperature, and the classic Argyll Robertson pupil (accommodates but does NOT react to light). General paresis presents with cognitive/psychiatric features and hyperreflexia.

A4. B - Neurosyphilis (reactive CSF VDRL) requires aqueous crystalline penicillin G IV 18-24 MU/day for 10-14 days - regardless of HIV status. Single-dose benzathine penicillin does NOT adequately penetrate the CNS.

A5. C - Jarisch-Herxheimer is a febrile reaction (fever, rigors, headache) within 2-8 hours of treating early syphilis. Caused by massive release of TNF-α, IL-6, IL-8 from lysed treponemes. NOT an allergy. Managed with antipyretics; do NOT stop penicillin.

A6. B - Gram-negative intracellular diplococci in PMNs = N. gonorrhoeae. Current first-line is ceftriaxone 500 mg IM (500mg-1g depending on local guidelines) as a single dose, due to widespread penicillin and fluoroquinolone resistance.

A7. B - Any gonorrhea diagnosis mandates concurrent testing for chlamydia, syphilis, and HIV. (Red Book 2021; Harrison's 22e)

A8. D - Painful indurated inguinal ulcer is NOT DGI. DGI presents with: migratory polyarthralgia → purulent monoarthritis, dermatitis (papulovesicular/pustular lesions on extremities), and tenosynovitis. The "ulcer" description fits chancroid or syphilis.

A9. C - N. gonorrhoeae has widespread resistance to penicillins, tetracyclines, and fluoroquinolones. Extended-spectrum cephalosporins (ceftriaxone) remain the treatment backbone. Emerging ceftriaxone-resistant strains are now an international concern.

A10. A - Uncomplicated urogenital chlamydia: doxycycline 100 mg BD x 7 days (preferred over azithromycin 1g single dose due to higher efficacy for urogenital infection). Test of cure is NOT routinely recommended except in pregnancy. (Harrison's 22e)

A11. C - Serovars L1, L2, L3 = LGV (invasive lymphatic disease). Serovars A, B, C = ocular trachoma (leading cause of preventable blindness). Serovars D-K = urogenital infections (most common STI).

A12. A - LGV proctitis: doxycycline 100 mg BD for 21 days (longer course needed for lymphogranulomatous tissue invasion vs. 7 days for non-LGV chlamydia).

A13. B - Neonatal chlamydial conjunctivitis typically appears at 5-14 days of life (vs. gonococcal at 2-5 days). Must screen for chlamydial pneumonia (onset 2-12 weeks of age with staccato cough, no fever). Treat with oral erythromycin or azithromycin.

A14. B - The correct differential:

HSV-2: multiple, painful, superficial vesicular ulcers
Syphilis: single, painless, indurated (hard chancre)
Chancroid: painful, ragged, deep, undermined edges
LGV: small transient papule/ulcer → inguinal bubo (the ulcer is often missed)

(Goldman-Cecil, Harrison's 22e)

A15. C - Chancroid (H. ducreyi): painful genital ulcer with undermined edges + fluctuant bubo. "School of fish" / "railway track" pattern on Gram stain (gram-negative coccobacilli in chains). Common in Asia/Africa.

A16. B - Donovanosis: Klebsiella granulomatis. Diagnostic hallmark = Donovan bodies (encapsulated gram-negative rods inside macrophage vacuoles) on Wright-Giemsa stain of crush prep from lesion tissue. Painless, progressive, beefy-red ulcerative lesion. No bubo formation.

A17. B - For recurrent genital HSV in pregnancy: acyclovir (or valacyclovir) suppression from 36 weeks gestation to reduce viral shedding and recurrence at delivery, lowering risk of neonatal HSV. Cesarean is indicated if active lesions at labor onset, not routinely for all HSV-positive women.

A18. B - This is a classic exam distinction. Primary syphilis chancre = single, firm, painless, indurated (patients often miss it). HSV ulcers = multiple, painful, superficial, vesicular/erosive with inflamed erythematous base. (Berek & Novak's Gynecology)

A19. A - Trichomonas vaginalis: flagellated protozoan causing frothy yellow-green discharge, vulvar pruritus, and strawberry cervix (petechial hemorrhages). Treatment: metronidazole 2g single dose OR 500 mg BD x 7 days - MUST treat sexual partner simultaneously.

A20. C - Bacterial vaginosis (Gardnerella/mixed anaerobes): pH >4.5, positive whiff test, clue cells on wet mount - Amsel criteria. Treatment: metronidazole 500 mg BD x 7 days (or clindamycin). Unlike trichomoniasis, partner treatment does NOT reduce recurrence.

A21. A - HPV 6 and 11 = genital warts (condylomata acuminata, low-risk). HPV 16 and 18 = high-risk for cervical, oropharyngeal, anal, and vulvar cancers. Covered by current vaccines (Gardasil 9 adds 31, 33, 45, 52, 58).

A22. B - Fitz-Hugh-Curtis syndrome = perihepatitis complicating PID from N. gonorrhoeae or C. trachomatis ascent to the liver capsule, causing RUQ pain and violin-string adhesions between liver and anterior peritoneum on laparoscopy.

A23. A - Post-PID sequelae: tubal-factor infertility (11% after 1 episode, 23% after 2, 54% after 3+), ectopic pregnancy (7x increased risk), and chronic pelvic pain. (Harrison's 22e)

A24. B - Key distinction:

RPR/VDRL (nontreponemal) = quantitative, titers fall with treatment, used to monitor response
FTA-ABS/TPHA (treponemal) = remain positive for life even after cure; used for confirmation

A 4-fold drop in RPR titer = adequate treatment response.

A25. B - Biologic false positive (BFP) RPR: reactive nontreponemal test + negative treponemal test = not syphilis. BFP causes include: SLE, pregnancy, malaria, viral infections, IV drug use, antiphospholipid syndrome. No treatment needed; investigate for underlying BFP cause.

HIGH-YIELD SUMMARY TABLE

Organism	Key Feature	Ulcer	Diagnosis	Treatment
T. pallidum	Painless chancre → rash → late manifestations	Single, indurated, painless	Darkfield + RPR/VDRL + FTA-ABS	Benzathine PCN G
N. gonorrhoeae	Purulent discharge, gram-neg diplococci	No ulcer (DGI = skin lesions)	Gram stain + NAAT	Ceftriaxone IM
C. trachomatis D-K	Mucopurulent discharge, often asymptomatic	No ulcer	NAAT	Doxycycline 7d
C. trachomatis L1-3 (LGV)	Inguinal bubo, proctitis in MSM	Small, transient	NAAT + PCR typing	Doxycycline 21d
H. ducreyi	Painful ulcer + bubo	Painful, undermined edges	"School of fish" Gram stain	Azithromycin 1g
K. granulomatis	Painless progressive ulcer, no bubo	Beefy-red, granulomatous	Donovan bodies (Wright-Giemsa)	Doxycycline
HSV-2	Painful vesicles/ulcers, recurrent	Multiple, painful, superficial	PCR / Tzanck smear	Acyclovir
T. vaginalis	Frothy green discharge, strawberry cervix	No ulcer	Wet mount - motile flagellates	Metronidazole

Let me know if you want deeper dives into any specific pathogen, more MCQs on a particular section, image-based questions, or a timed quiz format!

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