Infectious Diseases Practice Questions

Q: An adult man presents with the clinical condition shown in the image, and a Gram stain reveals Gram-negative diplococci. What is the most appropriate treatment?

Ceftriaxone. ***Ceftriaxone*** - The image shows **urethritis** (discharge from the urethra), and the Gram stain revealing **Gram-negative diplococci** is characteristic of **Neisseria gonorrhoeae**. - **Ceftriaxone** is the recommended first-line treatment for **gonorrhea**, often administered as a single intramuscular dose. *Azithromycin* - While often co-administered with ceftriaxone to cover potential **Chlamydia coinfection**, it is not the primary treatment for gonorrhea alone. - Azithromycin is the main treatment for uncomplicated **Chlamydia trachomatis** infections. *Doxycycline* - **Doxycycline** is a highly effective antibiotic for treating **Chlamydia trachomatis** infections and certain other bacterial STIs. - It is not the primary treatment for **gonorrhea** due to resistance concerns and preferred efficacy of cephalosporins. *Acyclovir* - **Acyclovir** is an antiviral medication used to treat infections caused by the **herpes simplex virus (HSV)**. - It has no activity against **bacterial infections** like gonorrhea, making it inappropriate for this presentation.

Q: A 25-year-old woman with HIV (CD4 count 320/μL) presents with vulvar ulceration for 3 weeks. Initial testing for HSV, syphilis, and chancroid is negative. Empiric treatment for these conditions does not improve the lesion. Biopsy shows a dense lymphoplasmacytic infiltrate with CMV inclusions. What is the most appropriate management?

Intravenous ganciclovir for 14-21 days. The biopsy showing **CMV inclusions** confirms **cytomegalovirus (CMV) infection** as the cause of the vulvar ulceration. **Ganciclovir** is the first-line antiviral treatment for serious CMV infections, especially in immunocompromised patients, and intravenous administration provides sufficient systemic efficacy. *Oral fluconazole for 14 days* - **Fluconazole** is an antifungal medication primarily used to treat candidiasis [1]. - It would be ineffective against **CMV**, which is a viral infection, and is not indicated for her current diagnosis. *Topical corticosteroids* - **Corticosteroids** are anti-inflammatory agents that could potentially worsen a viral infection by further suppressing the immune response [1]. - They do not address the underlying **CMV infection** and are therefore contraindicated as primary treatment for this condition. *Oral valacyclovir for 14 days* - **Valacyclovir** is an antiviral medication effective against **herpes simplex virus (HSV)** and **varicella-zoster virus (VZV)** [2]. - While initial HSV testing was negative, and valacyclovir is not effective against **CMV** [2].

Q: A 28-year-old man presents with recurrent urethritis despite appropriate treatment for gonorrhea and chlamydia. NAAT tests for both are negative. He reports adherence to therapy and denies reexposure. What is the most appropriate next step?

Testing for Mycoplasma genitalium. ***Testing for Mycoplasma genitalium*** - **Mycoplasma genitalium** is a common cause of **non-gonococcal urethritis** that is often resistant to standard gonorrhea and chlamydia treatments. [1] - Given the persistent symptoms despite appropriate treatment and negative NAAT for gonorrhea and chlamydia, testing for this organism is the most logical next step [1]. *HIV testing* - While HIV can affect immune function and increase susceptibility to infections, it is not a direct cause of recurrent urethritis that would require this as the immediate next diagnostic step in this specific scenario. - There are no symptoms mentioned that would specifically point towards an acute HIV infection or AIDS-defining illness causing the recurrent urethritis. *Repeat treatment with higher-dose azithromycin* - This is not appropriate without a confirmed pathogen, as empirical treatment with higher doses can contribute to **antimicrobial resistance**. - The patient has already received appropriate treatment, and repeating it without knowing the cause may delay accurate diagnosis and effective management. *Urologic evaluation for structural abnormalities* - While structural abnormalities could cause recurrent urinary tract symptoms, they are a less common cause of recurrent infectious urethritis in a young, otherwise healthy male. - A urologic evaluation would typically be considered after infectious causes, especially common and treatable STIs like **Mycoplasma genitalium**, have been ruled out [1].

Q: Which of the following best predicts the need for lumbar puncture in a patient with syphilis?

Neurological or ophthalmic signs. ***Neurological or ophthalmic signs*** - The presence of **neurological symptoms** (e.g., headache, confusion, motor deficits) or **ophthalmic abnormalities** (e.g., vision changes, uveitis) in a patient with syphilis strongly indicates central nervous system (CNS) involvement, necessitating a **lumbar puncture** to diagnose **neurosyphilis**. - These signs suggest the spirochete has invaded the CNS or eye, making CSF examination critical for confirming involvement and guiding treatment. *Presence of genital ulcers* - Genital ulcers are characteristic of **primary syphilis** and do not directly predict CNS involvement or the need for a lumbar puncture. - While they indicate active infection, the infection may not have progressed to the CNS at this stage. *History of prior treatment* - A history of prior treatment for syphilis, even if adequately treated, does not inherently indicate a need for lumbar puncture unless there is evidence of **treatment failure** or **neurosyphilis symptoms**. - Retreatment is usually guided by serological response or clinical symptoms, not just a history of prior treatment. *Positive VDRL test* - A positive **Venereal Disease Research Laboratory (VDRL)** test confirms active syphilis infection and is used for monitoring treatment response. - However, it does not specifically indicate CNS involvement and is not a sole predictor for performing a lumbar puncture without accompanying neurological or ophthalmological signs.

Q: A 30-year-old woman presents with dysuria, urinary frequency, and lower abdominal pain for 3 days. She has a new sexual partner. On examination, she has suprapubic tenderness but no cervical motion tenderness or vaginal discharge. Urine dipstick shows positive leukocyte esterase but negative nitrites. Microscopy reveals numerous WBCs but no bacteria. What is the most likely diagnosis and appropriate management?

Acute urethral syndrome due to C. trachomatis - Doxycycline. ### Acute urethral syndrome due to C. trachomatis - Doxycycline - The presence of **dysuria**, **frequency**, **pyuria** (leukocyte esterase, WBCs) without **bacteriuria** or positive nitrites, especially in a sexually active young woman with a new partner, is highly suggestive of **acute urethral syndrome** often caused by *Chlamydia trachomatis* [1]. - **Doxycycline** is the recommended first-line treatment for *Chlamydia trachomatis* infections [3]. *Gonorrheal urethritis - Ceftriaxone* - While *Neisseria gonorrhoeae* can cause **urethritis**, it typically presents with purulent urethral discharge, which is absent here [2]. - While Ceftriaxone is appropriate for gonorrhea, the clinical picture and lab findings (no bacteria, high WBCs) are more consistent with chlamydia [3]. *Interstitial cystitis - Pain management and urinary analgesics* - **Interstitial cystitis** typically presents with chronic (more than 6 weeks) pelvic pain, urinary urgency, and frequency, often without evidence of infection or a clear trigger like a new sexual partner. - The acute onset and clear inflammatory markers (pyuria) make this diagnosis less likely. *Acute bacterial cystitis - Empiric antibiotic therapy* - Although there is **dysuria** and **frequency**, the **absence of nitrites** and **bacteria** on microscopy and dipstick makes bacterial cystitis less likely. - The presence of pyuria without bacteriuria in this context points to urethritis, likely non-gonococcal [1].

Q: A 22-year-old man presents with urethral discharge and dysuria for 3 days. Gram stain shows intracellular gram-negative diplococci. Two weeks after appropriate treatment, he returns with similar symptoms. Repeat testing shows no organisms on Gram stain but leukocytes are present. What is the most likely explanation?

Concurrent chlamydial infection. ***Concurrent chlamydial infection*** - The initial presentation was consistent with **gonorrhea** (intracellular gram-negative diplococci). After initial treatment, the recurrence of symptoms with **leukocytes but no organisms on Gram stain** is highly suggestive of a co-existing infection that would not be visible on Gram stain or sensitive to the initial gonorrhea treatment [1]. - **Chlamydial infections** are frequently co-transmitted with gonorrhea and present with similar symptoms, often causing **post-gonococcal urethritis** when the gonorrhea is treated but the chlamydia is not [3]. *Antibiotic resistance* - If it were antibiotic resistance, the **intracellular gram-negative diplococci** would likely still be present on repeat Gram stain after treatment, rather than absent. - While possible, the absence of organisms on repeat Gram stain makes this less likely than a co-infection with a pathogen not detectable by Gram stain. *Reinfection with N. gonorrhoeae* - Reinfection would imply a new exposure and would again show **intracellular gram-negative diplococci** on Gram stain, which are explicitly stated to be absent. - Although possible, the rapid recurrence (2 weeks) and absence of the original organism make another pathogen more probable. *Urethral stricture* - A urethral stricture could cause persistent or recurrent symptoms like dysuria and discharge, but it would not typically be associated with the acute presence of **leukocytes** in the absence of an active infection. - Strictures are mechanical issues and would not explain the initial finding of gram-negative diplococci or the subsequent sterile pyuria [2].

Q: How does HIV infection alter the natural history of syphilis?

Increased risk of neurosyphilis. Increased risk of neurosyphilis - HIV infection causes **immunosuppression**, impairing the host's ability to contain *Treponema pallidum*, leading to more aggressive dissemination to the central nervous system. - This increased vulnerability means that **neurosyphilis** can occur earlier in the course of the syphilis infection and may be more challenging to treat effectively. *Elimination of secondary stage* - HIV infection does **not eliminate** or bypass the secondary stage of syphilis; in fact, the **rash and mucocutaneous lesions** might be more atypical or severe due to immunosuppression. - The disease progression remains largely similar in its stages, though manifestations can be altered. *Reduced serological response* - While some HIV-infected individuals may have **atypical serological responses**, particularly those with severe immunodeficiency, it does **not universally reduce** the serological response. - Many HIV-infected individuals with syphilis still show typical antibody responses, although **false-negative results** can occur. *Faster progression to tertiary stage* - While HIV can lead to **more aggressive syphilis** and an increased risk of complications like neurosyphilis, there is **no clear evidence** that it consistently accelerates progression to the tertiary stage. - Tertiary syphilis still typically develops many years after the initial infection, though **cardiovascular and gummatous syphilis** can also be more severe.

Q: A patient living with HIV presents with foulsmelling stools. Microscopic examination of the stool reveals no cysts or ova, but a 200-micrometer larva is observed. What is the most likely pathogen?

Strongyloides stercoralis. ***Strongyloides stercoralis*** - The presence of **larvae** in the stool [2], particularly **rhabditiform larvae**, is characteristic of *Strongyloides stercoralis* infection, as this parasite has an **autoinfective cycle** involving larval stages in the human host [2]. - In HIV-positive patients, *Strongyloides* can cause **hyperinfection syndrome**, leading to severe gastrointestinal symptoms like foul-smelling stools, and increased larval shedding [2]. *Ascaris lumbricoides* - *Ascaris lumbricoides* is a large intestinal nematode, but it typically presents with **ova** (eggs) in the stool, not larvae, as the eggs hatch in the small intestine. - While it can cause gastrointestinal symptoms, the hallmark microscopic finding in stool samples is the presence of **mammillated or decorticated eggs**. *Ancylostoma duodenale* - *Ancylostoma duodenale* (hookworm) infections are identified by the presence of **eggs** in the stool [1], which are typically oval with a thin shell and contain a developing larva. - Hookworm larvae usually develop in **soil** and infect humans through skin penetration, rather than being commonly found in stool samples from intestinal infection [1]. *Schistosoma mansoni* - *Schistosoma mansoni* is a **blood fluke** that causes intestinal schistosomiasis, characterized by the presence of **spined eggs** in the stool. - The parasite's life cycle involves **freshwater snails** as intermediate hosts, and a **larval stage (cercariae)** that penetrates human skin, but larvae are not typically found in human stool.

Q: A farmer presents with severe leg pain, fever, chills, retro-orbital pain, and bilateral conjunctival suffusion. What is the most likely diagnosis?

Leptospirosis. **Leptospirosis** - The combination of **leg pain**, **fever**, chills, **retro-orbital pain**, and **bilateral conjunctival suffusion** (red eyes without frank pus) in a farmer (occupational exposure to contaminated water/soil) is highly suggestive of **leptospirosis** [1]. - **Conjunctival suffusion** is a classic and distinctive sign of leptospirosis, differentiating it from many other febrile illnesses [1]. *Dengue fever* - While dengue fever can present with **fever**, **retro-orbital pain**, and **myalgia**, **conjunctival suffusion** is not a typical feature, and severe leg pain is less emphasized compared to leptospirosis [2]. - Dengue is also common in tropical/subtropical regions but the specific constellation of symptoms points away from it [2]. *Malaria* - Malaria presents with classic **cyclic fevers**, **chills**, and **sweats**, often accompanied by headache and muscle aches, and sometimes hepatosplenomegaly. - **Conjunctival suffusion** and severe leg pain are not characteristic features of uncomplicated malaria [2]. *Rickettsia infection* - Rickettsial infections (e.g., Rocky Mountain spotted fever, scrub typhus) often present with **fever**, **headache**, and a **rash**, which can be maculopapular or petechial [3]. - **Retro-orbital pain** and **conjunctival suffusion** are not typical symptoms, and a distinctive rash is generally a key diagnostic clue for rickettsial diseases [3].

Question 1

An adult man presents with the clinical condition shown in the image, and a Gram stain reveals Gram-negative diplococci. What is the most appropriate treatment?

Accepted Answer

Ceftriaxone

Answer

Azithromycin

Answer

Doxycycline

Answer

Acyclovir

Question 2

A 25-year-old woman with HIV (CD4 count 320/μL) presents with vulvar ulceration for 3 weeks. Initial testing for HSV, syphilis, and chancroid is negative. Empiric treatment for these conditions does not improve the lesion. Biopsy shows a dense lymphoplasmacytic infiltrate with CMV inclusions. What is the most appropriate management?

Accepted Answer

Intravenous ganciclovir for 14-21 days

Answer

Oral fluconazole for 14 days

Answer

Topical corticosteroids

Answer

Oral valacyclovir for 14 days

Question 3

A 28-year-old man presents with recurrent urethritis despite appropriate treatment for gonorrhea and chlamydia. NAAT tests for both are negative. He reports adherence to therapy and denies reexposure. What is the most appropriate next step?

Accepted Answer

Testing for Mycoplasma genitalium

Answer

HIV testing

Answer

Repeat treatment with higher-dose azithromycin

Answer

Urologic evaluation for structural abnormalities

Question 4

Which of the following best predicts the need for lumbar puncture in a patient with syphilis?

Accepted Answer

Neurological or ophthalmic signs

Answer

Presence of genital ulcers

Answer

History of prior treatment

Answer

Positive VDRL test

Question 5

A 30-year-old woman presents with dysuria, urinary frequency, and lower abdominal pain for 3 days. She has a new sexual partner. On examination, she has suprapubic tenderness but no cervical motion tenderness or vaginal discharge. Urine dipstick shows positive leukocyte esterase but negative nitrites. Microscopy reveals numerous WBCs but no bacteria. What is the most likely diagnosis and appropriate management?

Accepted Answer

Acute urethral syndrome due to C. trachomatis - Doxycycline

Answer

Gonorrheal urethritis - Ceftriaxone

Answer

Interstitial cystitis - Pain management and urinary analgesics

Answer

Acute bacterial cystitis - Empiric antibiotic therapy

Question 6

A 27-year-old HIV-positive man (CD4 count 250/μL) presents with a 2-month history of perianal ulcer that is painless, clean-based, and indurated. Dark field microscopy and PCR for HSV are negative. VDRL is 1:64, and TPHA is positive. Lumbar puncture shows 30 WBCs (predominantly lymphocytes) and CSF-VDRL is reactive. Despite receiving standard benzathine penicillin therapy 2 weeks ago, the ulcer persists unchanged. What is the most appropriate next step?

Accepted Answer

Aqueous crystalline penicillin G 18-24 million units IV daily for 14 days

Answer

Repeat benzathine penicillin G 2.4 MU IM weekly for 3 weeks

Answer

Doxycycline 100mg twice daily for 28 days

Answer

Biopsy of the lesion to rule out malignancy

Question 7

A 22-year-old man presents with urethral discharge and dysuria for 3 days. Gram stain shows intracellular gram-negative diplococci. Two weeks after appropriate treatment, he returns with similar symptoms. Repeat testing shows no organisms on Gram stain but leukocytes are present. What is the most likely explanation?

Accepted Answer

Concurrent chlamydial infection

Answer

Antibiotic resistance

Answer

Reinfection with N. gonorrhoeae

Answer

Urethral stricture

Question 8

How does HIV infection alter the natural history of syphilis?

Accepted Answer

Increased risk of neurosyphilis

Answer

Elimination of secondary stage

Answer

Reduced serological response

Answer

Faster progression to tertiary stage

Question 9

A patient living with HIV presents with foulsmelling stools. Microscopic examination of the stool reveals no cysts or ova, but a 200-micrometer larva is observed. What is the most likely pathogen?

Accepted Answer

Strongyloides stercoralis

Answer

Ascaris lumbricoides

Answer

Ancylostoma duodenale

Answer

Schistosoma mansoni

Question 10

A farmer presents with severe leg pain, fever, chills, retro-orbital pain, and bilateral conjunctival suffusion. What is the most likely diagnosis?

Accepted Answer

Leptospirosis

Answer

Dengue fever

Answer

Malaria

Answer

Rickettsia infection

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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