Infectious Diseases — MCQs

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.

Q1115

In a patient with AIDS and a CD4 count of fewer than 50 cells/µL, which of the following opportunistic infections is most likely to occur?

Q1116

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?

Q1117

A patient with diabetes presents with a black eschar on the nose and facial swelling. A biopsy shows broad, non-septate hyphal elements with right-angle branching. Assess the likely diagnosis and the urgency of the management required.

Q1118

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?

Q1119

A 55-year-old man presents with fever, chills, and hematuria. He has a history of travel to sub-Saharan Africa, and a blood smear shows schistosomes. What is the most likely diagnosis?

Q1120

According to current evidence and emerging guidelines, what is the preferred primary treatment for initial Clostridium difficile infection in adults?

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 1111: 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 1112: 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 1113: A patient presents with a bull's-eye rash and flu-like symptoms following a tick bite. What is the most likely diagnosis?

A. Rocky Mountain spotted fever
B. Lyme disease (Correct Answer)
C. Ehrlichiosis
D. Anaplasmosis

Explanation: ***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.

Question 1114: 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.

A. Pneumocystis pneumonia; TMP-SMX and steroids (Correct Answer)
B. Pulmonary embolism; anticoagulation
C. Acute lupus pneumonitis; increased steroids
D. Bacterial pneumonia; IV antibiotics

Explanation: ***Pneumocystis pneumonia; TMP-SMX and steroids*** - The patient's immunosuppressed status due to **systemic lupus erythematosus** and **prednisone** use [4], combined with **fever**, **cough**, **bilateral patchy infiltrates** on chest X-ray [3], and **leukopenia** (WBC 3,000) [1], are all highly suggestive of **Pneumocystis pneumonia (PCP)**. - **Trimethoprim-sulfamethoxazole (TMP-SMX)** is the first-line treatment for PCP, and **corticosteroids** are often added for moderate to severe cases to reduce inflammation [3]. *Pulmonary embolism; anticoagulation* - While **pleuritic chest pain** can be a symptom of pulmonary embolism (PE), the presence of **fever**, **cough**, and **bilateral patchy infiltrates** makes PE less likely as the primary diagnosis. Patients with SLE and antiphospholipid antibodies are, however, at increased risk for thromboembolism [2]. - PE is typically characterized by hypoxia and a normal chest X-ray, or findings like **Westermark sign** or **Hampton's hump**, which are not described here. *Acute lupus pneumonitis; increased steroids* - **Acute lupus pneumonitis** is a possible complication of SLE, but it usually presents with **rapid onset dyspnea**, **hypoxemia**, and more often **lobar or diffuse alveolar infiltrates**, sometimes with hemorrhage [2]. - While it might require increased steroids, the significant **leukopenia** and the specific X-ray findings (patchy infiltrates) are more characteristic of an opportunistic infection in an immunocompromised patient than a lupus flare in the lungs. *Bacterial pneumonia; IV antibiotics* - While **bacterial pneumonia** can cause fever, cough, and infiltrates, the **bilateral patchy infiltrates** are less typical for most bacterial pneumonias which often present with **lobar consolidation**. - More importantly, bacterial pneumonia in an immunocompromised patient typically presents with a **high white blood cell count**, not leukopenia, making it a less likely primary diagnosis in this context [1].

Question 1115: In a patient with AIDS and a CD4 count of fewer than 50 cells/µL, which of the following opportunistic infections is most likely to occur?

A. Cryptococcus neoformans (Correct Answer)
B. Candida albicans
C. Aspergillus fumigatus
D. Histoplasma capsulatum

Explanation: ***Cryptococcus neoformans*** - **Cryptococcal meningitis** is a common and severe opportunistic infection in AIDS patients with **CD4 counts below 50 cells/µL** [1]. - It often presents with **headache**, **fever**, **nuchal rigidity**, and altered mental status. *Candida albicans* - While common in AIDS patients, **oral candidiasis (thrush)** typically occurs at **higher CD4 counts** (e.g., below 200 cells/µL) and is less indicative of a CD4 count below 50 cells/µL compared to cryptococcosis [2]. - Systemic candidiasis is less common than oral or esophageal forms in this setting [1]. *Aspergillus fumigatus* - **Aspergillosis** is typically seen in patients with **severe neutropenia** and profound immunosuppression, often related to hematological malignancies or transplant, rather than solely based on low CD4 count in AIDS. - It is less likely to be the *most likely* opportunistic infection at a CD4 count of fewer than 50 cells/µL in an HIV patient presenting with typical symptoms of opportunistic infection. *Histoplasma capsulatum* - **Disseminated histoplasmosis** can occur in AIDS patients with CD4 counts below 100-150 cells/µL, but it is **geographically localized** to endemic areas (e.g., Ohio and Mississippi River valleys) [3]. - Cryptococcal meningitis is more universally prevalent in AIDS patients with very low CD4 counts, making it a more likely general answer.

Question 1116: 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?

A. Start antibiotics based on clinical suspicion
B. Repeat the rapid antigen test
C. Perform a throat culture (Correct Answer)
D. Prescribe symptomatic treatment only

Explanation: ***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.

Question 1117: A patient with diabetes presents with a black eschar on the nose and facial swelling. A biopsy shows broad, non-septate hyphal elements with right-angle branching. Assess the likely diagnosis and the urgency of the management required.

A. Aspergillosis, elective treatment
B. Mucormycosis, immediate aggressive treatment (Correct Answer)
C. Candidiasis, standard antifungal treatment
D. Dermatophytosis, topical treatment

Explanation: ***Mucormycosis, immediate aggressive treatment*** - The presence of a **black eschar**, **facial swelling** in a diabetic patient, and biopsy findings of **broad, non-septate hyphal elements with right-angle branching** are classic for **mucormycosis** [1]. - This is an **opportunistic fungal infection** that is rapidly progressive and highly fatal, requiring **immediate aggressive treatment** including surgical debridement and antifungal therapy (e.g., amphotericin B) [1]. *Aspergillosis, elective treatment* - **Aspergillosis** typically presents with **septate hyphae with acute angle branching**, which differs from the *non-septate, right-angle branching* seen in the biopsy. - While serious, it does not typically manifest with a **black eschar** as the primary sign of rhino-orbital-cerebral involvement; also, the urgency described for mucormycosis is much higher than for most forms of aspergillosis. *Candidiasis, standard antifungal treatment* - **Candidiasis** usually presents with **pseudohyphae and budding yeasts**; it does not exhibit the *broad, non-septate hyphal elements* described. - While fungal, it rarely causes a **necrotic black eschar** in the absence of severe systemic involvement in immunocompromised patients, and its treatment regimen is generally less urgent and aggressive than for mucormycosis. *Dermatophytosis, topical treatment* - **Dermatophytosis (ringworm)** is a **superficial fungal infection** of the skin, hair, or nails, typically presenting with *erythematous, scaly lesions*. - It would not cause a **black eschar** or facial swelling indicative of deep tissue invasion, nor would the biopsy show *broad, non-septate hyphae* in the manner described.

Question 1118: 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?

A. Atypical pneumonia in immunocompromised setting
B. Gram-positive bacterial pneumonia in immunocompromised patient
C. Fungal pneumonia in neutropenic patient (Correct Answer)
D. Respiratory infection in immunocompromised host

Explanation: **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 1119: A 55-year-old man presents with fever, chills, and hematuria. He has a history of travel to sub-Saharan Africa, and a blood smear shows schistosomes. What is the most likely diagnosis?

A. Malaria
B. Schistosomiasis (Correct Answer)
C. Leptospirosis
D. Typhoid fever

Explanation: Schistosomiasis - The presence of schistosomes on a blood smear directly confirms the diagnosis of schistosomiasis. - Hematuria is a classic symptom, particularly with Schistosoma haematobium infection which is common in sub-Saharan Africa [1]. Malaria - Characterized by periodic fevers, chills, and sweats [2], but the blood smear would show Plasmodium parasites, not schistosomes. - While common in sub-Saharan Africa, the specific finding of schistosomes rules out malaria as the primary diagnosis [2]. Leptospirosis - Presents with fever, chills, headache, muscle pain, and can involve renal dysfunction [3], but is caused by bacteria (Leptospira species), not parasites. - Diagnosis is typically by serology or PCR, and blood smears would not show schistosomes. Typhoid fever - Symptoms include sustained fever, headache, abdominal pain, and sometimes rash, caused by Salmonella Typhi bacteria. - Diagnosis is made by blood or stool cultures, and it does not involve hematuria or schistosomes on a blood smear.

Question 1120: According to current evidence and emerging guidelines, what is the preferred primary treatment for initial Clostridium difficile infection in adults?

A. Fidaxomicin (Correct Answer)
B. Rifaximin
C. Vancomycin
D. Metronidazole

Explanation: Fidaxomicin - **Fidaxomicin** is a macrocyclic antibiotic that has demonstrated superior sustained clinical response rates compared to vancomycin for initial episodes of *C. difficile* infection, especially in preventing recurrence. - Its **narrow spectrum of activity** minimizes disruption to the gut microbiome, which is crucial for preventing subsequent infections. *Metronidazole* - While previously used for mild-to-moderate *C. difficile* infection (CDI), **metronidazole** is no longer recommended as primary therapy due to its inferior efficacy compared to vancomycin or fidaxomicin [1]. - Its use is generally reserved for situations where **vancomycin or fidaxomicin are unavailable**, or in very specific, mild cases [1]. *Vancomycin* - **Oral vancomycin** is an effective treatment for *C. difficile* infection and was long considered a first-line option [1]. However, evidence suggests fidaxomicin may be superior, particularly in preventing recurrence. - It is still a highly effective treatment for CDI, especially for **initial episodes that are moderate to severe**, but fidaxomicin offers an advantage in sustained response. *Rifaximin* - **Rifaximin** is primarily used to prevent recurrence of *C. difficile* infection after an initial course of vancomycin, rather than as a primary treatment. - It is a **non-absorbable antibiotic** with limited utility as a standalone initial therapy for active CDI.

Practice by Chapter

Principles of Antimicrobial Therapy

Practice Questions

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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