Infectious Diseases Practice Questions

Q: A 35-year-old male with HIV presents with watery diarrhea, abdominal pain, and weight loss. Stool examination shows acid-fast oocysts. Analyze and determine the most likely diagnosis and initial management.

Cryptosporidiosis; initiate antiretroviral therapy. ***Cryptosporidiosis; initiate antiretroviral therapy*** - The presence of **watery diarrhea**, **abdominal pain**, **weight loss**, and **acid-fast oocysts** in a patient with **HIV** is highly suggestive of **Cryptosporidium parvum** infection [1]. - While **supportive care** is essential, the most effective long-term management for **cryptosporidiosis** in HIV patients is **immune reconstitution** through **antiretroviral therapy (ART)** [1]. *Mycobacterium avium complex; start azithromycin* - **MAC infection** typically causes **fever**, **night sweats**, **weight loss**, and **diarrhea**, but stool examination would show **acid-fast bacilli**, not oocysts [1]. - While **azithromycin** is used for MAC treatment and prophylaxis, it is not indicated for cryptosporidiosis. *Cytomegalovirus colitis; initiate ganciclovir* - **CMV colitis** in HIV patients presents with **bloody diarrhea**, **abdominal pain**, and potentially **fever**, which differs from the watery diarrhea described. - Diagnosis is usually made via **colonoscopy with biopsy** showing intranuclear inclusions, not acid-fast oocysts in stool. *Giardiasis; treat with metronidazole* - **Giardiasis** causes **watery, foul-smelling diarrhea**, **abdominal cramps**, and **bloating**, but stool examination would show **trophozoites** or **cysts**, which are not acid-fast. - **Metronidazole** is the standard treatment for giardiasis, but it is ineffective against Cryptosporidium.

Q: A healthcare worker presents with fever, muscle pain, and fatigue. Serological tests are positive for HCV RNA. Which treatment option is considered first-line for hepatitis C?

Direct-acting antivirals. ***Direct-acting antivirals*** - **Direct-acting antivirals (DAAs)** are the current first-line treatment for chronic hepatitis C virus (HCV) infection due to their high efficacy, improved tolerability, and shorter treatment durations compared to older therapies. [1] - DAAs target specific viral proteins crucial for HCV replication, leading to **high sustained virologic response (SVR) rates**, often exceeding 95%. *Interferon-alpha* - **Interferon-alpha** was previously a cornerstone of HCV treatment but has largely been replaced by DAAs due to its significant side effects (e.g., flu-like symptoms, depression) and lower cure rates. [2] - Its mechanism involves modulating the host immune response rather than directly inhibiting viral replication, making it less specific and associated with more systemic adverse events. *Lamivudine* - **Lamivudine** is an antiviral drug primarily used in the treatment of **hepatitis B virus (HBV)** and human immunodeficiency virus (HIV) infections, not HCV. - It functions as a **nucleoside reverse transcriptase inhibitor**, and while it has some activity against HCV in vitro, it is not clinically effective as a monotherapy for hepatitis C. *Ribavirin* - **Ribavirin** is an antiviral medication that was commonly used in combination with interferon-alpha for HCV treatment in the past. - It is currently used in **combination with DAAs** in certain difficult-to-treat cases (e.g., decompensated cirrhosis, prior treatment failure) but is not effective as a monotherapy and is not considered a first-line agent on its own.

Q: A patient presents with fever and jaundice after repairing sewers. What is the most appropriate test to diagnose the infection in this patient?

Microscopic agglutination test. ***Microscopic agglutination test*** - The patient's presentation (fever, jaundice, history of repairing sewers) is highly suggestive of **leptospirosis** [1]. The **Microscopic Agglutination Test (MAT)** is considered the gold standard for diagnosing leptospirosis, as it directly detects antibodies against *Leptospira* serovars [1]. - MAT provides **serovar-specific results** and is highly sensitive and specific, especially when acute and convalescent phase sera are tested [1]. *Weil Felix test* - The Weil-Felix test is used to diagnose **rickettsial infections**, not leptospirosis. - It detects antibodies that cross-react with antigens of certain *Proteus* species. *Paul Bunnell test* - The Paul-Bunnell test is used to detect **heterophile antibodies** associated with **infectious mononucleosis** (Epstein-Barr virus infection). - This test is not relevant for diagnosing bacterial infections like leptospirosis. *Microimmunofluorescence test* - The microimmunofluorescence (MIF) test is primarily used for the diagnosis of **chlamydial infections** and sometimes for rickettsial diseases. - While an antibody-detection test, it is not the standard or preferred method for diagnosing leptospirosis.

Q: What is the first-line treatment for acute bacterial meningitis in adults?

Ceftriaxone. ***Ceftriaxone*** - **Ceftriaxone** is a broad-spectrum **third-generation cephalosporin** that provides excellent penetration into the **cerebrospinal fluid (CSF)** and covers common bacterial meningitis pathogens like *Streptococcus pneumoniae* and *Neisseria meningitidis* [1]. - Its efficacy against these key pathogens and good safety profile make it the **first-line empirical treatment** for acute bacterial meningitis in adults, often used in combination with **vancomycin** to cover resistant strains [1], [2]. *Amoxicillin* - While an effective antibiotic for certain bacterial infections, **amoxicillin** does **not provide adequate coverage** for the typical pathogens causing acute bacterial meningitis, especially *Neisseria meningitidis*. - Its **CSF penetration** is generally insufficient to reliably treat meningitis, particularly for severe cases or resistant strains. *Vancomycin* - **Vancomycin** is crucial in the treatment of bacterial meningitis, particularly for covering **penicillin-resistant *Streptococcus pneumoniae*** and **methicillin-resistant *Staphylococcus aureus* (MRSA)** [2]. - However, it is typically used in **combination with a third-generation cephalosporin** like ceftriaxone, rather than as monotherapy, because it has a slower bactericidal effect and less optimal CSF penetration compared to ceftriaxone for initial broad coverage. *Doxycycline* - **Doxycycline** is a tetracycline antibiotic primarily used for atypical bacterial infections, such as those caused by **Rickettsia, Mycoplasma, or Chlamydia**. - It is **not effective** against the primary bacterial culprits of acute meningitis like *S. pneumoniae* or *N. meningitidis* and lacks the necessary bactericidal activity for this severe infection.

Q: A patient presents with ulcerative lesions and lymphadenopathy. PCR of lesion swabs is positive for Bartonella henselae DNA. What is the most likely diagnosis?

Cat scratch disease. ***Cat scratch disease*** - The presence of **ulcerative lesions**, **lymphadenopathy**, and a positive **PCR for Bartonella henselae DNA** are pathognomonic for cat scratch disease. - This condition is caused by **Bartonella henselae** and transmitted through a cat scratch or bite, typically from a kitten. *Tuberculosis* - While tuberculosis can cause **lymphadenopathy**, it usually presents with **pulmonary symptoms** such as chronic cough, fever, and weight loss. - **Ulcerative skin lesions** are less typical in primary tuberculosis and would not be associated with **Bartonella henselae**. *Syphilis* - Syphilis presents with **chancres** (**painless ulcers**) in the primary stage and widespread **lymphadenopathy**. - However, the causative agent is **Treponema pallidum**, which would not yield a positive PCR for **Bartonella henselae**. *Lymphogranuloma venereum* - This is a sexually transmitted infection caused by specific serovars of **Chlamydia trachomatis**, leading to **genital ulcers** and **inguinal lymphadenopathy** (**buboes**). - The presentation is not associated with **Bartonella henselae infection**.

Q: A patient with COVID-19 develops severe ARDS despite receiving dexamethasone. What additional treatment option could target the underlying inflammatory process?

Tocilizumab. ***Tocilizumab*** - **Tocilizumab** is an **IL-6 receptor blocker** that can be considered in severe COVID-19 with ARDS, especially when there's evidence of a cytokine storm despite corticosteroids. - It works by inhibiting the pro-inflammatory effects of **interleukin-6 (IL-6)**, a key mediator in severe COVID-19 inflammation. *Remdesivir* - **Remdesivir** is an **antiviral medication** that directly inhibits viral replication, but it does not directly target the inflammatory process leading to ARDS. - Its benefit is primarily seen in reducing recovery time and preventing progression to severe disease, not in managing established severe inflammation or ARDS. *Ivermectin* - **Ivermectin** is an **antiparasitic drug** that has been investigated for COVID-19, but there is no strong evidence from large, well-designed clinical trials to support its use for treating or preventing COVID-19, especially not for ARDS related to inflammation. - Its mechanism of action is not related to modulating the inflammatory pathways involved in severe COVID-19 ARDS. *Azithromycin* - **Azithromycin** is an **antibiotic** with some anti-inflammatory properties, but its efficacy in directly treating severe COVID-19 or ARDS has not been consistently demonstrated. - It's mainly used to treat bacterial co-infections and doesn't target the primary immunological drivers of severe COVID-19 ARDS like IL-6.

Q: A 22-year-old male with a sore throat, fever, and swollen lymph nodes presents with white patches on his tonsils. A rapid antigen detection test is negative. What is the next best step?

Perform a throat culture. ***Perform a throat culture*** - A negative **rapid antigen detection test (RADT)** does not completely rule out **streptococcal pharyngitis**, especially in highly suspicious cases. - A **throat culture** is the **gold standard** for diagnosing Group A Streptococcus (GAS) and is necessary to confirm the diagnosis and guide appropriate antibiotic treatment. *Start antibiotics based on clinical suspicion* - While clinical suspicion for **strep throat** is high, starting antibiotics without confirmation could contribute to **antibiotic resistance** and unnecessary side effects if the infection is viral. - Due to the potential for viral etiologies presenting similarly, it's crucial to confirm bacterial infection before initiating treatment. *Repeat the rapid antigen test* - Repeating the **RADT** may still yield a false negative, as its sensitivity is not 100%. - Given the high clinical suspicion and the potential for complications if untreated, a more definitive test is warranted. *Prescribe symptomatic treatment only* - While symptomatic treatment is appropriate for **viral pharyngitis**, untreated **bacterial strep throat** can lead to serious complications such as **rheumatic fever** or **glomerulonephritis**. - Without confirming the absence of a bacterial infection, simply providing symptomatic relief would be negligent.

Q: A patient presents with a bull's-eye rash and flu-like symptoms following a tick bite. What is the most likely diagnosis?

Lyme disease. ***Lyme disease*** - The classic **bull's-eye rash** (erythema migrans) is a hallmark sign of early **Lyme disease**, often accompanied by **flu-like symptoms** after a tick bite [1]. - This presentation is highly indicative of infection with **Borrelia burgdorferi**, transmitted by **Ixodes ticks** [1]. *Rocky Mountain spotted fever* - Characterized by a **maculopapular rash** that typically starts on the **ankles and wrists** and spreads centrally, often becoming **petechial**. - While it follows a tick bite and can present with flu-like symptoms, the rash is not described as a **bull's-eye**. *Ehrlichiosis* - Symptoms include **fever, headache, malaise**, and **muscle aches** after a tick bite [1]. - A rash is less common and, if present, is usually **maculopapular** or **petechial**, not the characteristic bull's-eye. *Anaplasmosis* - Presents with **fever, chills, headache**, and **myalgia** following a tick bite, similar to other tick-borne illnesses. - It does **not typically cause a rash**, distinguishing it from Lyme disease and RMSF.

Q: A patient with acute myelogenous leukemia develops severe neutropenia following chemotherapy. He presents with fever and multiple nodular lung infiltrates. What are the likely pathogens and the preferred empirical therapy?

Fungal pneumonia in neutropenic patient. **Fungal pneumonia in neutropenic patient** - The presence of **fever**, **neutropenia**, and **multiple nodular lung infiltrates** in an acute myelogenous leukemia patient post-chemotherapy is highly suggestive of **invasive fungal infection**, particularly aspergillosis [1]. - **Empirical antifungal therapy**, such as voriconazole or a lipid formulation of amphotericin B, is crucial in this high-risk population given the high mortality associated with delayed treatment [2]. *Gram-positive bacterial pneumonia in immunocompromised patient* - While gram-positive bacteria can cause pneumonia in neutropenic patients, **nodular lung infiltrates** are less typical for common bacterial pneumonias which often present with lobar consolidation. - Bacterial pneumonia might be considered, but the risk of fungal infection is paramount given the clinical scenario, necessitating broader coverage. *Atypical pneumonia in immunocompromised setting* - **Atypical pneumonias** (e.g., *Mycoplasma, Chlamydophila, Legionella*) generally cause interstitial infiltrates, not typically multiple distinct nodules. - While possible, the immune status and radiological findings steer away from atypical bacterial pathogens as the primary concern. *Respiratory infection in immunocompromised host* - This is too broad and does not specify the likely pathogens or preferred therapy to address the critical situation [3]. - The clinical presentation demands a more targeted approach, prioritizing the most dangerous and likely organisms like fungi, which are strongly suggested by the nodular infiltrates in a neutropenic patient [1].

Question 1

A 35-year-old male with HIV presents with watery diarrhea, abdominal pain, and weight loss. Stool examination shows acid-fast oocysts. Analyze and determine the most likely diagnosis and initial management.

Accepted Answer

Cryptosporidiosis; initiate antiretroviral therapy

Answer

Mycobacterium avium complex; start azithromycin

Answer

Cytomegalovirus colitis; initiate ganciclovir

Answer

Giardiasis; treat with metronidazole

Question 2

A healthcare worker presents with fever, muscle pain, and fatigue. Serological tests are positive for HCV RNA. Which treatment option is considered first-line for hepatitis C?

Accepted Answer

Direct-acting antivirals

Answer

Lamivudine

Answer

Interferon-alpha

Answer

Ribavirin

Question 3

A patient presents with fever and jaundice after repairing sewers. What is the most appropriate test to diagnose the infection in this patient?

Accepted Answer

Microscopic agglutination test

Answer

Weil Felix test

Answer

Paul Bunnell test

Answer

Microimmunofluorescence test

Question 4

What is the first-line treatment for acute bacterial meningitis in adults?

Accepted Answer

Ceftriaxone

Answer

Amoxicillin

Answer

Vancomycin

Answer

Doxycycline

Question 5

A patient presents with ulcerative lesions and lymphadenopathy. PCR of lesion swabs is positive for Bartonella henselae DNA. What is the most likely diagnosis?

Accepted Answer

Cat scratch disease

Answer

Tuberculosis

Answer

Syphilis

Answer

Lymphogranuloma venereum

Question 6

A patient with COVID-19 develops severe ARDS despite receiving dexamethasone. What additional treatment option could target the underlying inflammatory process?

Accepted Answer

Tocilizumab

Answer

Remdesivir

Answer

Ivermectin

Answer

Azithromycin

Question 7

A 22-year-old male with a sore throat, fever, and swollen lymph nodes presents with white patches on his tonsils. A rapid antigen detection test is negative. What is the next best step?

Accepted Answer

Perform a throat culture

Answer

Start antibiotics based on clinical suspicion

Answer

Repeat the rapid antigen test

Answer

Prescribe symptomatic treatment only

Question 8

A patient presents with a bull's-eye rash and flu-like symptoms following a tick bite. What is the most likely diagnosis?

Accepted Answer

Lyme disease

Answer

Rocky Mountain spotted fever

Answer

Ehrlichiosis

Answer

Anaplasmosis

Question 9

A 53-year-old female with a history of systemic lupus erythematosus on prednisone presents with fever, cough, and pleuritic chest pain. Chest X-ray shows bilateral patchy infiltrates. Laboratory results indicate a white blood cell count of 3,000 and creatinine level of 1.4. Analyze and determine the diagnosis and initial treatment.

Accepted Answer

Pneumocystis pneumonia; TMP-SMX and steroids

Answer

Pulmonary embolism; anticoagulation

Answer

Acute lupus pneumonitis; increased steroids

Answer

Bacterial pneumonia; IV antibiotics

Question 10

A patient with acute myelogenous leukemia develops severe neutropenia following chemotherapy. He presents with fever and multiple nodular lung infiltrates. What are the likely pathogens and the preferred empirical therapy?

Accepted Answer

Fungal pneumonia in neutropenic patient

Answer

Atypical pneumonia in immunocompromised setting

Answer

Gram-positive bacterial pneumonia in immunocompromised patient

Answer

Respiratory infection in immunocompromised host

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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