Sexually transmitted infections US Medical PG Practice Questions and MCQs
Practice US Medical PG questions for Sexually transmitted infections. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Sexually transmitted infections US Medical PG Question 1: A 35-year-old woman visits the office with complaints of yellowish vaginal discharge and increased urinary frequency for a week. She also complains of pain during urination. Past medical history is irrelevant. She admits to having multiple sexual partners in the past few months. Physical examination is within normal limits except for lower abdominal tenderness. Urine culture yields Chlamydia trachomatis. What is the most appropriate next step in the management of this patient?
- A. Acyclovir
- B. Doxycycline (Correct Answer)
- C. Metronidazole
- D. Clindamycin
- E. Boric acid
Sexually transmitted infections Explanation: ***Doxycycline***
- **Doxycycline** is a recommended first-line treatment for **Chlamydia trachomatis** infections (along with azithromycin).
- A 7-day course of **doxycycline 100 mg orally twice daily** is highly effective in eradicating the infection.
- **Alternative:** Azithromycin 1 g PO single dose is also first-line and may be preferred for compliance.
*Acyclovir*
- **Acyclovir** is an antiviral medication used to treat **herpes simplex virus (HSV)** infections.
- It is ineffective against **bacterial infections** like Chlamydia.
*Metronidazole*
- **Metronidazole** is an antibiotic primarily used for **anaerobic bacterial** and **parasitic infections** (e.g., bacterial vaginosis, trichomoniasis).
- It is not effective against **Chlamydia trachomatis**.
*Clindamycin*
- **Clindamycin** is an antibiotic effective against a range of **bacterial infections**, including some anaerobic bacteria.
- However, it is not a recommended treatment for **Chlamydia trachomatis** infections.
*Boric acid*
- **Boric acid** is an antifungal agent primarily used for treating **recurrent vulvovaginal candidiasis** (yeast infections).
- It has no role in treating **bacterial infections** like Chlamydia.
Sexually transmitted infections US Medical PG Question 2: A 28-year-old woman comes to the physician because of a 4-day history of lower abdominal pain and pain with urination. Five months ago, she was treated for gonococcal urethritis. She recently moved in with her newlywed husband. She is sexually active with her husband and they do not use condoms. Her only medication is an oral contraceptive. Her temperature is 37.5°C (99.7°F) and blood pressure is 120/74 mm Hg. There is tenderness to palpation over the pelvic region. Pelvic examination shows a normal-appearing vulva and vagina. Laboratory studies show:
Leukocyte count 8,400/mm3
Urine
pH 6.7
Protein trace
WBC 60/hpf
Nitrites positive
Bacteria positive
Which of the following is the most likely causal organism?
- A. Enterococcus faecalis
- B. Klebsiella pneumoniae
- C. Neisseria gonorrhoeae
- D. Escherichia coli (Correct Answer)
- E. Staphylococcus saprophyticus
Sexually transmitted infections Explanation: ***Escherichia coli***
- The presence of **nitrites** in the urine analysis strongly suggests a urinary tract infection caused by a **nitrate-reducing bacterium**, such as *E. coli*.
- *E. coli* is the **most common cause of uncomplicated UTIs**, especially in sexually active women, and the symptoms (lower abdominal pain, dysuria, pyuria, bacteriuria) are classic for a UTI.
*Enterococcus faecalis*
- While *Enterococcus faecalis* can cause UTIs, it is **less common** than *E. coli* in uncomplicated cases and typically **does not produce nitrites** in urine due to lacking nitrate reductase.
- It is more commonly associated with UTIs in hospitalized patients or those with urinary tract abnormalities.
*Klebsiella pneumoniae*
- *Klebsiella pneumoniae* can cause UTIs and is a **nitrite-producing bacterium**, but it is a **less frequent cause** of community-acquired uncomplicated UTIs compared to *E. coli*.
- It is more often associated with healthcare-associated infections or UTIs in compromised hosts.
*Neisseria gonorrhoeae*
- While the patient has a history of gonococcal urethritis, current symptoms are more consistent with a UTI, and *Neisseria gonorrhoeae* is a **rare cause of cystitis** or pyelonephritis.
- Gonorrhea primarily causes urethritis, cervicitis, or pelvic inflammatory disease, and **does not typically produce nitrites** from nitrates in urine.
*Staphylococcus saprophyticus*
- *Staphylococcus saprophyticus* is a common cause of UTIs in young, sexually active women, but it is **nitrite-negative** because it does not possess nitrate reductase.
- The positive nitrites in the urine make *E. coli* a more likely culprit in this case.
Sexually transmitted infections US Medical PG Question 3: A 24-year-old man presents with a painless genital ulcer for the past 2 weeks. He reports that he recently has been having unprotected sex with multiple partners. Past medical history is unremarkable. On physical examination, a single ulcer is present on the dorsal shaft of the penis which is circumscribed, indurated, and partially healed. There is moderate inguinal lymphadenopathy but no buboes. Which of the following tests would confirm the most likely diagnosis in this patient?
- A. Perform a darkfield microscopic examination of a swab from the chancre (Correct Answer)
- B. Swab the chancre and perform a saline wet mount
- C. Fluorescent treponemal antibody absorption (FTA-ABS) test
- D. Frei test
- E. Venereal Disease Research Laboratory (VDRL) test
Sexually transmitted infections Explanation: ***Perform a darkfield microscopic examination of a swab from the chancre***
- This patient's presentation with a **painless, indurated genital ulcer** (chancre) and regional lymphadenopathy is highly suggestive of **primary syphilis**.
- **Darkfield microscopy** directly visualizes the spirochetes (**_Treponema pallidum_**) from the chancre, providing a definitive and rapid diagnosis.
*Swab the chancre and perform a saline wet mount*
- A **saline wet mount** is used to identify mobile organisms like **_Trichomonas vaginalis_** or clue cells suggestive of **bacterial vaginosis**, neither of which are associated with this type of ulcer.
- This test would not reveal the spirochetes responsible for syphilis and is not appropriate for diagnosing a genital ulcer.
*Fluorescent treponemal antibody absorption (FTA-ABS) test*
- The **FTA-ABS test** is a **treponemal-specific serological test** used to confirm a syphilis diagnosis, particularly in later stages or when non-treponemal tests are reactive.
- While sensitive for syphilis, it's typically reactive later in the disease course and cannot directly visualize the bacteria from the ulcer, making darkfield microscopy a more immediate and direct diagnostic tool for primary syphilis.
*Frei test*
- The **Frei test** is an obsolete intradermal skin test used to diagnose **lymphogranuloma venereum (LGV)**, which typically presents with a transient, unnoticed lesion followed by severe lymphadenopathy and buboes.
- It is not used for the diagnosis of syphilis and would not be helpful for this patient's presentation.
*Viral and rickettsial disease research laboratory (VDRL) test*
- The **VDRL test** is a **non-treponemal serological test** for syphilis that detects antibodies against cardiolipin, a lipid released from damaged host cells.
- While used for screening and monitoring treatment response, it can be **negative in early primary syphilis** (before seroconversion) and may not be positive at the time of presentation with a fresh chancre.
Sexually transmitted infections US Medical PG Question 4: A 36-year-old woman comes to the physician for an annual pelvic examination and Pap smear. Her last Pap smear was 3 years ago. She has been sexually active with multiple male partners and takes an oral contraceptive. She has smoked one pack of cigarettes daily for 10 years. Pelvic examination shows no abnormalities. A photomicrograph of cervical cells from the Pap smear specimen is shown. Cells similar to the one indicated by the arrow are most likely to be seen in which of the following conditions?
- A. Condylomata acuminata (Correct Answer)
- B. Bacterial vaginosis
- C. Trichomoniasis
- D. Genital herpes
- E. Syphilitic chancre
Sexually transmitted infections Explanation: ***Condylomata acuminata***
- The image likely depicts a **koilocyte**, a key indicator of **Human Papillomavirus (HPV) infection**, which causes condylomata acuminata.
- Koilocytes are characterized by **perinuclear cytoplasmic vacuolization** and nuclear atypia, directly linked to HPV.
*Bacterial vaginosis*
- Characterized by a **shift in vaginal flora**, presenting with "clue cells" (vaginal epithelial cells covered in bacteria) and discharge, not koilocytes.
- While common, bacterial vaginosis does not cause the **cytopathic changes** seen with HPV infection.
*Trichomoniasis*
- Caused by the **protozoan parasite** *Trichomonas vaginalis*, leading to a frothy, green-yellow discharge and cervical inflammation (strawberry cervix).
- Diagnosis involves identifying the **motile trichomonads** on wet mount, not koilocytes on a Pap smear.
*Genital herpes*
- Caused by **herpes simplex virus (HSV)**, resulting in painful vesicular lesions that ulcerate.
- Cytologic findings include **multinucleated giant cells** with nuclear molding and intranuclear inclusions, distinctly different from koilocytes.
*Syphilitic chancre*
- A primary lesion of syphilis caused by **_Treponema pallidum_**, presenting as a painless ulcer.
- Diagnosis is made by **darkfield microscopy** or serologic tests; cytology is not used to identify syphilitic chancres.
Sexually transmitted infections US Medical PG Question 5: A 28-year-old woman comes to the emergency department for a rash that began 3 days ago. She has low-grade fever and muscle aches. She has no history of serious illness and takes no medications. She has had 5 male sexual partners over the past year and uses condoms inconsistently. Her temperature is 38.1°C (100.6° F), pulse is 85/min, and blood pressure is 126/89 mm Hg. Examination shows a diffuse maculopapular rash that includes the palms and soles. The remainder of the examination shows no abnormalities. A venereal disease research laboratory (VDRL) test is positive. Which of the following is the next appropriate step in management?
- A. Intravenous penicillin G
- B. Dark field microscopy
- C. Treponemal culture
- D. Oral doxycycline
- E. Fluorescent treponemal antibody absorption test (Correct Answer)
Sexually transmitted infections Explanation: ***Fluorescent treponemal antibody absorption test***
- A positive **VDRL** (a non-treponemal test) should be confirmed with a **treponemal-specific test** like the **fluorescent treponemal antibody absorption (FTA-ABS)** test or **Treponema pallidum particle agglutination (TPPA)** assay to definitively diagnose syphilis.
- This confirmatory step helps differentiate true syphilis from false-positive VDRL results, which can occur in autoimmune diseases (SLE, antiphospholipid syndrome), other infections (malaria, mononucleosis), pregnancy, or recent vaccination.
- While this patient's presentation is highly suggestive of **secondary syphilis** (diffuse maculopapular rash involving palms and soles, fever, myalgias, positive VDRL), confirmatory testing is the standard next step before initiating treatment.
- Note: In some clinical settings with classic secondary syphilis, immediate treatment may be initiated, but confirmatory testing remains the most appropriate next diagnostic step.
*Intravenous penicillin G*
- IV aqueous penicillin G is the treatment for **neurosyphilis**, not uncomplicated secondary syphilis.
- **Secondary syphilis** is treated with **intramuscular benzathine penicillin G 2.4 million units** as a single dose.
- Treatment should follow confirmed diagnosis with treponemal-specific testing.
*Dark field microscopy*
- This technique visualizes spirochetes directly from **primary lesions** (chancres) or moist secondary lesions (condyloma lata, mucous patches).
- It is not practical for this patient who has a diffuse maculopapular rash without obvious mucosal or genital lesions.
- Dark-field microscopy requires specialized equipment and expertise not readily available in most emergency departments.
*Treponemal culture*
- **Treponema pallidum** cannot be cultured on artificial media because it is an **obligate pathogen** that requires living host cells.
- Culture is not a diagnostic option for syphilis.
*Oral doxycycline*
- **Doxycycline 100 mg twice daily for 14 days** is an alternative treatment for early syphilis in **penicillin-allergic patients**.
- Treatment should only be initiated after diagnosis is confirmed with treponemal-specific testing.
- This is not the next appropriate step; confirmatory testing comes first.
Sexually transmitted infections US Medical PG Question 6: A 22-year-old female college student presents to the clinic with complaints of intense vaginal itching and a painful sensation when urinating. She also notes that she has felt more lethargic and has additionally been experiencing recent fevers and headaches. She says that she is sexually active and occasionally uses condoms. On physical exam, she is found to have red, vesicular ulcers on her labia that are painful to palpation and tender inguinal lymphadenopathy. What is the most likely pathogen causing her presentation?
- A. Chlamydia trachomatis
- B. Klebsiella granulomatis
- C. Treponema pallidum
- D. Herpes simplex virus type 2 (Correct Answer)
- E. Herpes simplex virus type 1
Sexually transmitted infections Explanation: ***Herpes simplex virus type 2***
- The presence of **red, vesicular ulcers on the labia** that are painful, along with **tender inguinal lymphadenopathy**, fevers, headaches, and lethargy, are classic signs of a primary HSV-2 infection.
- HSV-2 is the most common cause of **genital herpes**, leading to painful vesicular or ulcerative lesions in the genital area.
*Chlamydia trachomatis*
- This pathogen typically causes **urethritis**, **cervicitis**, or **pelvic inflammatory disease (PID)**, often with minimal or no symptoms, or with discharge or dysuria.
- It does not typically present with **painful vesicular or ulcerative lesions** and systemic symptoms like fever and headache are less common.
*Klebsiella granulomatis*
- This bacterium causes **granuloma inguinale (donovanosis)**, characterized by progressive, painless, beefy red **ulcers** with rolled borders, not vesicles.
- The lesions are typically **not painful** and do not usually present with systemic symptoms like fever and headache in the initial stages.
*Treponema pallidum*
- The primary stage of syphilis, caused by *Treponema pallidum*, presents as a **painless chancre**, which is a firm, indurated ulcer.
- The lesions in this patient are described as **painful and vesicular**, which is inconsistent with a syphilitic chancre.
*Herpes simplex virus type 1*
- While HSV-1 can cause genital herpes, it is more commonly associated with **oral herpes (cold sores)**.
- Genital HSV-1 infections are typically **less severe** and **recur less frequently** than HSV-2 infections.
Sexually transmitted infections US Medical PG Question 7: An endocervical swab is performed and nucleic acid amplification testing via polymerase chain reaction is conducted. It is positive for Chlamydia trachomatis and negative for Neisseria gonorrhoeae. Which of the following is the most appropriate pharmacotherapy?
- A. Oral azithromycin (Correct Answer)
- B. Intramuscular ceftriaxone plus oral azithromycin
- C. Oral doxycycline
- D. Intramuscular ceftriaxone
- E. Intravenous cefoxitin plus oral doxycycline
Sexually transmitted infections Explanation: ***Oral azithromycin***
- A single 1-gram oral dose of **azithromycin** is a highly effective and convenient first-line treatment for uncomplicated **Chlamydia trachomatis** infections.
- Its long half-life allows for once-daily dosing, improving patient adherence.
*Intramuscular ceftriaxone plus oral azithromycin*
- This combination therapy is primarily used for suspected or confirmed **gonorrhea** and chlamydia coinfection, particularly if N. gonorrhoeae cannot be ruled out.
- Since **Neisseria gonorrhoeae** was explicitly negative, the ceftriaxone component is unnecessary.
*Oral doxycycline*
- **Doxycycline** (100 mg twice daily for 7 days) is an alternative first-line treatment for **Chlamydia trachomatis** infections and is highly effective.
- However, azithromycin is often preferred for its single-dose regimen which can improve treatment adherence, especially in asymptomatic patients.
*Intramuscular ceftriaxone*
- **Ceftriaxone** is the primary treatment for **Neisseria gonorrhoeae** infections.
- As the test for **N. gonorrhoeae** was negative, this treatment is not indicated for the current patient's diagnosis.
*Intravenous cefoxitin plus oral doxycycline*
- This regimen is typically reserved for more severe infections, such as **pelvic inflammatory disease (PID)**, often requiring hospitalization, which is not indicated by the simple positive chlamydia swab.
- Administering **IV cefoxitin** is an escalation beyond what is necessary for uncomplicated chlamydial cervicitis.
Sexually transmitted infections US Medical PG Question 8: A 34-year-old man presents with multiple painful ulcers on his penis. He says that the ulcers all appeared suddenly at the same time 3 days ago. He reports that he is sexually active with multiple partners and uses condoms inconsistently. He is afebrile and his vital signs are within normal limits. Physical examination reveals multiple small shallow ulcers with an erythematous base and without discharge. There is significant inguinal lymphadenopathy present. Which of the following is the most likely etiologic agent of this patient’s ulcers?
- A. Human papillomavirus
- B. Chlamydia trachomatis
- C. Treponema pallidum
- D. Haemophilus ducreyi
- E. Herpes simplex virus (Correct Answer)
Sexually transmitted infections Explanation: ***Herpes simplex virus***
- This patient's presentation of multiple **painful shallow ulcers** with an **erythematous base** that appeared suddenly, along with significant **inguinal lymphadenopathy**, is highly consistent with **genital herpes** caused by HSV.
- HSV lesions typically appear in **clusters** and are often painful, in contrast to the single, painless chancre of syphilis.
*Human papillomavirus*
- HPV infection primarily causes **genital warts (condyloma acuminata)**, which are usually soft, fleshy, and non-painful growths, not ulcers.
- While HPV can cause epithelial lesions, they are not typically described as painful, shallow ulcers.
*Chlamydia trachomatis*
- *Chlamydia trachomatis* typically causes **urethritis**, cervicitis, or **lymphogranuloma venereum (LGV)**, the latter of which involves painful inguinal lymphadenopathy and sometimes secondary ulcers, but the initial lesion is often a small, transient, painless ulcer or papule.
- The sudden onset of multiple painful shallow ulcers is not characteristic of typical *C. trachomatis* infections.
*Treponema pallidum*
- *Treponema pallidum* (syphilis) causes a **painless, firm, singular chancre** in the primary stage, which is very different from the multiple painful shallow ulcers described.
- While syphilis can cause lymphadenopathy, the ulcer itself is usually not painful.
*Haemophilus ducreyi*
- *Haemophilus ducreyi* causes **chancroid**, which presents as **deep, painful ulcers** with ragged, undermined borders and frequently causes **suppurative (pus-forming) inguinal lymphadenopathy**.
- Although painful ulcers are present, the description of "shallow ulcers" with an erythematous base is less typical for chancroid.
Sexually transmitted infections US Medical PG Question 9: A 27-year-old woman visits your office with a 3-day complaint of fever, malaise, myalgias, and headaches associated with vulvar itching, vulvar soreness, dysuria, and urethral discharge. The pain when urinating is so severe that she has attempted to avoid the use of the toilet. She just returned from a spring break in the tropics and explains that she had multiple unprotected sexual encounters with men and women. Upon physical examination, the temperature was 38.7°C (101.6°F) and the heart rate was 90/min. The pelvic examination revealed vulvar ulcers, vulvar excoriations, erythema, vaginal mucosa edema, and ulcerative cervicitis. Which of the following will best aid you in the identification of the specific organism causing the above symptoms?
- A. Location of the lesions
- B. Culture in Thayer-Martin agar
- C. Direct fluorescence antigen (Correct Answer)
- D. Serology
- E. Tzanck smear
Sexually transmitted infections Explanation: ***Direct fluorescence antigen***
- A **direct fluorescence antigen (DFA)** test can rapidly identify viral antigens from the lesions, specifically for **Herpes Simplex Virus (HSV)**, which is highly suspected given the patient's symptoms (fever, malaise, myalgias, vulvar ulcers, dysuria, and recent unprotected sexual encounters).
- **HSV** is a common cause of genital ulcers, and DFA offers a quick, sensitive, and specific method for detection directly from clinical samples.
*Location of the lesions*
- While the **location of the lesions** (vulvar ulcers) is characteristic of several sexually transmitted infections (STIs), it is not specific enough to identify the *specific organism* without further laboratory testing.
- Conditions like syphilis, chancroid, and HSV all cause genital ulcers, making location alone insufficient for definitive diagnosis.
*Culture in Thayer-Martin agar*
- **Thayer-Martin agar** is selectively used for culturing **Neisseria gonorrhoeae**, which causes gonorrhea.
- Although the patient has urethral discharge and dysuria, the presence of **vulvar ulcers** and systemic symptoms like fever and myalgias point away from uncomplicated gonorrhea.
*Serology*
- **Serology** detects antibodies to pathogens, indicating past or present infection, but is often less useful for identifying the *acute* causative organism in the initial stages of a symptomatic outbreak like this one.
- For instance, HSV serology can distinguish between HSV-1 and HSV-2 exposure but does not confirm active infection in the way direct antigen methods or PCR do.
*Tzanck smear*
- A **Tzanck smear** can reveal characteristic **multinucleated giant cells** and **intranuclear inclusions**, which are indicative of herpesvirus infections (HSV or VZV).
- However, it is less sensitive and specific than a direct fluorescence antigen test or PCR, and results can be variable depending on the quality of the smear and interpretation.
Sexually transmitted infections US Medical PG Question 10: A 32-year-old man comes to the physician because of severe burning with urination for the past 3 days. During this period, he has had clear urethral discharge early in the morning. He has no history of serious illness, except for a rash following treatment with erythromycin 20 years ago. The patient takes no medications. He is sexually active with one male and one female partner; they use condoms inconsistently. His younger brother was diagnosed with Crohn disease at the age of 24 years. The patient does not smoke. He drinks one to two beers on weekends. He appears well. Temperature is 36.8°C (98°F), pulse is 75/min, and blood pressure is 135/78 mm Hg. Physical examination shows no abnormalities. Gram stain of a urethral swab shows neutrophils but no organisms. Which of the following is the most likely causal pathogen?
- A. Adenovirus
- B. Herpes simplex virus
- C. Neisseria gonorrhoeae
- D. Chlamydia trachomatis (Correct Answer)
- E. Trichomonas vaginalis
Sexually transmitted infections Explanation: ***Chlamydia trachomatis***
- The presentation of **dysuria** (burning with urination), **clear urethral discharge**, and a **Gram stain showing neutrophils but no organisms** is highly characteristic of **non-gonococcal urethritis**, with *Chlamydia trachomatis* being the most common cause.
- The patient's **inconsistent condom use** and **multiple sexual partners** increase the risk of sexually transmitted infections like chlamydia.
*Adenovirus*
- Adenovirus can cause **urethritis**, but it is more commonly associated with symptoms like **pharyngitis**, **conjunctivitis**, and **acute respiratory disease**.
- While it can cause clear discharge, the clinical picture is more suggestive of a common STI.
*Herpes simplex virus*
- Herpes simplex virus (HSV) typically causes **painful genital ulcers or vesicles**, not primarily clear urethral discharge, although it can cause dysuria if the urethra is involved.
- The absence of external lesions and the presence of persistent discharge make HSV less likely.
*Neisseria gonorrhoeae*
- **Gonococcal urethritis** typically presents with a **purulent** (creamy, yellow, or greenish) urethral discharge and frequently shows **Gram-negative intracellular diplococci** on microscopy.
- The **clear discharge** and **absence of organisms** on Gram stain rule out *Neisseria gonorrhoeae* as the cause of this presentation.
*Trichomonas vaginalis*
- *Trichomonas vaginalis* can cause **urethritis** with discharge, but the discharge is typically described as **frothy**, **yellowish-green**, and associated with **itching**.
- While Gram stain might show neutrophils without other organisms, the classic discharge description and common co-occurrence with vaginitis in female partners are not present.
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