Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 1101: A 55-year-old farmer from the Midwest presents with a chronic cough and weight loss. A chest X-ray shows calcified granulomas, and a sputum culture reveals a dimorphic fungus. What is the most likely diagnosis?

A. Coccidioidomycosis
B. Blastomycosis
C. Histoplasmosis (Correct Answer)
D. Paracoccidioidomycosis

Explanation: ***Histoplasmosis*** - This fungus is endemic to the **Midwest** (Ohio and Mississippi river valleys) and is often associated with exposure to **bird or bat droppings**. - **Calcified granulomas** on chest X-ray and a **dimorphic fungus** on sputum culture are classic findings in chronic histoplasmosis. Chronic marks of the disease are typically managed with long-term antifungal therapy [1]. *Coccidioidomycosis* - This fungus is primarily found in the **Southwestern United States** and parts of Mexico and Central/South America ("desert rheumatism"). - While it can cause pulmonary symptoms and granulomas, its endemic region does not match the patient's geographic location. *Blastomycosis* - Blastomycosis is also endemic to the **Midwest** but commonly presents with skin lesions, bone involvement, and lung disease with broader-based budding yeast. - While it can cause pulmonary issues, the presence of **calcified granulomas** points more specifically towards histoplasmosis. *Paracoccidioidomycosis* - This fungal infection is largely restricted to **Central and South America**, making it highly unlikely for a patient from the Midwest to acquire it without travel history. - It typically presents with chronic progressive pulmonary disease and mucocutaneous lesions, with characteristic "pilot wheel" yeast forms.

Question 1102: A patient presents with fever and jaundice after repairing sewers. What is the most appropriate test to diagnose the infection in this patient?

A. Weil Felix test
B. Paul Bunnell test
C. Microscopic agglutination test (Correct Answer)
D. Microimmunofluorescence test

Explanation: ***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.

Question 1103: A patient presents with fever, eschar, and regional lymphadenopathy after hiking in an area known for mite infestation. What is the most likely diagnosis?

A. Rocky Mountain spotted fever
B. Typhus
C. Scrub typhus (Correct Answer)
D. Lyme disease

Explanation: ***Scrub typhus*** - The classic triad of **fever**, an **eschar** at the bite site, and **regional lymphadenopathy** in an endemic area (often associated with mite exposure) is highly indicative of scrub typhus [1]. - Caused by **_Orientia tsutsugamushi_**, transmitted by the bite of infected **chiggers** (larval mites) [1]. *Rocky Mountain spotted fever* - Characterized by a **maculopapular rash** that typically begins on the wrists and ankles and spreads centrally, often involving palms and soles. - While it can present with fever and may be tick-borne, the presence of an **eschar is atypical**. *Typhus* - Includes **epidemic typhus** (lice-borne, caused by _Rickettsia prowazekii_) and **murine typhus** (flea-borne, caused by _Rickettsia typhi_) [2]. - Both forms primarily present with **fever and rash** (macular or maculopapular) but generally **do not feature an eschar** at the bite site [2]. *Lyme disease* - The hallmark is **erythema migrans**, a characteristic bull's-eye rash, along with fever, headache, and fatigue. - It is a **tick-borne illness** but an **eschar is not a typical presentation**, and the rash is distinct from that seen in scrub typhus.

Question 1104: What is the first-line treatment for acute bacterial meningitis in adults?

A. Ceftriaxone (Correct Answer)
B. Amoxicillin
C. Vancomycin
D. Doxycycline

Explanation: ***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.

Question 1105: 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?

A. Direct-acting antivirals (Correct Answer)
B. Lamivudine
C. Interferon-alpha
D. Ribavirin

Explanation: ***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.

Question 1106: 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.

A. Cryptosporidiosis; initiate antiretroviral therapy (Correct Answer)
B. Mycobacterium avium complex; start azithromycin
C. Cytomegalovirus colitis; initiate ganciclovir
D. Giardiasis; treat with metronidazole

Explanation: ***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.

Question 1107: A 45-year-old female presents with abdominal pain, jaundice, and fever. An abdominal CT scan reveals multiple liver abscesses, and aspiration yields anchovy paste-like pus. What is the most likely etiological agent responsible for these findings?

A. Entamoeba histolytica (Correct Answer)
B. Staphylococcus aureus
C. Klebsiella pneumoniae
D. Echinococcus granulosus

Explanation: ***Entamoeba histolytica*** - The combination of **abdominal pain**, **jaundice**, **fever**, and **multiple liver abscesses** with **anchovy paste-like pus** is highly characteristic of an **amebic liver abscess** caused by *Entamoeba histolytica* [1]. - This parasite is acquired through the **fecal-oral route** and can invade the intestinal wall, leading to extraintestinal dissemination, most commonly to the liver [1]. *Echinococcus granulosus* - This pathogen causes **hydatid cysts**, which are typically **single**, large cysts with an **acellular fluid** rather than a purulent or "anchovy paste-like" consistency [2]. - While it can cause abdominal pain and jaundice, the pus description is not consistent with **hydatid disease** [2]. *Staphylococcus aureus* - **Pyogenic liver abscesses** caused by *Staphylococcus aureus* typically present with **fever** and **abdominal pain** but commonly involve **multiple smaller abscesses** and the pus is typically **creamy** and foul-smelling, not resembling "anchovy paste." - These are often associated with a primary source of infection, such as **bacteremia**. *Klebsiella pneumoniae* - **Klebsiella pneumoniae** is a common cause of **pyogenic liver abscesses**, particularly in patients with **diabetes mellitus**, and can present with fever, abdominal pain, and jaundice [2]. - However, the pus from a *Klebsiella* abscess is typically **thick and purulent** but lacks the distinctive **"anchovy paste" appearance** seen in amebic abscesses.

Question 1108: A patient with a recent history of antibiotic use develops severe diarrhea, and the stool sample tests positive for a toxin. What is the likely diagnosis?

A. Salmonella gastroenteritis
B. Campylobacter jejuni infection
C. Clostridioides difficile infection (Correct Answer)
D. Shigella dysenteriae infection

Explanation: ***Clostridioides difficile infection*** - **Clostridioides difficile infection (CDI)** is strongly associated with recent **antibiotic use** and presents with severe diarrhea due to toxin production [1]. - The **toxin test** for *C. difficile* in stool is the gold standard for diagnosis [1]. *Salmonella gastroenteritis* - While *Salmonella* can cause **diarrhea**, it is typically acquired through contaminated food or water, and antibiotic use is not a primary risk factor. - Diagnosis usually relies on a **stool culture**, not a toxin test. *Campylobacter jejuni infection* - *Campylobacter jejuni* causes **gastroenteritis** with bloody diarrhea but is acquired through contaminated food, particularly poultry, and is not directly linked to prior antibiotic use. - Diagnosis is primarily by **stool culture**. *Shigella dysenteriae infection* - **Shigellosis** is characterized by severe, often bloody diarrhea (**dysentery**) and can produce toxins, but its onset is not directly linked to prior antibiotic use. - Diagnosis is typically confirmed by **stool culture**.

Question 1109: A patient presents with ulcerative lesions and lymphadenopathy. PCR of lesion swabs is positive for Bartonella henselae DNA. What is the most likely diagnosis?

A. Cat scratch disease (Correct Answer)
B. Tuberculosis
C. Syphilis
D. Lymphogranuloma venereum

Explanation: ***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**.

Question 1110: Which part of the spine is most frequently affected by tuberculosis (Pott's disease)?

A. Cervical spine
B. Thoracic spine (Correct Answer)
C. Lumbar spine
D. Sacral spine

Explanation: ***Thoracic spine*** - The **thoracic spine** is the most common site for **Pott's disease** (tuberculous spondylitis) [1] due to its larger blood supply and potential for slower vertebral blood flow, allowing bacterial seeding. - Involvement often leads to **vertebral body collapse** and subsequent **kyphosis** (gibbus deformity), which is a classic presentation of spinal tuberculosis [1]. *Cervical spine* - While it can be affected, the **cervical spine** is less commonly involved in Pott's disease compared to the thoracic and lumbar regions. - Cervical involvement is often associated with **neurological deficits** due to the narrower spinal canal. *Lumbar spine* - The **lumbar spine** is the second most common site for Pott's disease, frequently presenting with **back pain** and **psoas abscess formation** [1]. - While significant, it is less frequently affected than the thoracic spine by tuberculosis. *Sacral spine* - The **sacral spine** is rarely the primary site of Pott's disease. - When it occurs, it is often due to direct extension from adjacent disease or as part of disseminated tuberculosis.

Practice by Chapter

Principles of Antimicrobial Therapy

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Fever of Unknown Origin

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HIV/AIDS and Related Infections

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Tuberculosis and Mycobacterial Diseases

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Tropical and Parasitic Infections

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Viral Infections (Hepatitis, Herpes, etc.)

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Healthcare-Associated Infections

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Fungal Infections

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Sepsis and Septic Shock

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Infection in Immunocompromised Hosts

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Emerging and Re-emerging Infections

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Antimicrobial Resistance

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Vaccination Principles

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