Infectious Diseases Practice Questions

Q: A patient presents with a painless genital ulcer followed by painful inguinal buboes (lymphadenopathy). Which strains of Chlamydia trachomatis are responsible for this condition?

L1–L3. ***L1–L3*** - These serovars of **Chlamydia trachomatis** are the causative agents of **lymphogranuloma venereum (LGV)**, a sexually transmitted infection. - The clinical presentation involves a transient, **painless genital ulcer** followed by the classic development of **painful inguinal lymphadenopathy** (buboes). *A, B, C* - These serovars are responsible for causing **trachoma**, a chronic keratoconjunctivitis that is the leading infectious cause of blindness worldwide. - They are typically transmitted via direct or indirect contact with eye, nose, or throat secretions rather than sexual contact. *D–K* - These strains cause common **sexually transmitted infections** including **urethritis**, **cervicitis**, and **pelvic inflammatory disease (PID)**. - They are the most frequent cause of bacterial sexually transmitted infections in developed countries but do not typically present with the pronounced **lymphadenopathy** seen in LGV. *B, C, D* - This grouping combines serovars associated with **trachoma** (B, C) and those causing **urogenital infections** (D), making it clinically incorrect. - There is no specific pathological entity associated with this collective group of **Chlamydia trachomatis** serovars.

Q: A 32-year-old woman with a history of splenectomy presents to the emergency department with sudden-onset high-grade fever, vomiting, hypotension, and rapidly progressive septic shock. Her symptoms began 2 weeks after a minor febrile illness. Which organism is the most likely causative agent of this life-threatening condition?

Streptococcus pneumoniae. ***Streptococcus pneumoniae*** - Patients with **asplenia** (post-splenectomy) are at significantly increased risk for overwhelming post-splenectomy infection (OPSI) due to defective clearance of **encapsulated organisms**. - *Streptococcus pneumoniae* is the most common cause of sepsis in asplenic patients, characterized by fulminant disease progression, high mortality rates, and rapid development of **septic shock**. *Escherichia coli* - While *Escherichia coli* is a common cause of sepsis (particularly urosepsis and intra-abdominal infections), it is not the classic pathogen associated with the unique susceptibility of the **asplenic patient**. - It lacks the specific capsular polysaccharide susceptibility profile that makes *S. pneumoniae* the primary concern in individuals without a functional **spleen**. *Staphylococcus aureus* - *Staphylococcus aureus* is a leading cause of skin and soft tissue infections, endocarditis, and osteomyelitis, but it is not typically characterized as an **encapsulated organism** that targets asplenic individuals. - The clinical presentation of rapid-onset septic shock following minor illness is more classic for the **fulminant course** of a pneumococcal infection in this specific patient demographic. *Pseudomonas aeruginosa* - *Pseudomonas aeruginosa* is an important cause of sepsis especially in **immunocompromised** or hospitalized patients, but it is not the most frequent pathogen associated with asplenia. - It generally presents in settings such as **ventilator-associated pneumonia**, burn wounds, or neutropenic fever, rather than the classic OPSI syndrome triggered by circulating **encapsulated bacteria**.

Q: A 65-year-old diabetic male presents with high-grade fever, productive rust-coloured sputum, and right-sided pleuritic chest pain for 3 days. His oxygen saturation is 88% on room air. A sputum Gram stain is performed (Image 1). Which of the following tests would most definitively confirm the identity of this organism from a positive blood culture?

A. Optochin sensitivity and bile solubility. ***A. Optochin sensitivity and bile solubility*** - The clinical presentation of **rust-colored sputum** and Gram stain showing **lancet-shaped diplococci** confirms *Streptococcus pneumoniae*. - This organism is definitively identified by its **sensitivity to optochin** (Ethylhydrocupreine) and its **solubility in bile** salts, which distinguishes it from other alpha-hemolytic streptococci. *B. CAMP test and hippurate hydrolysis* - These tests are used for the identification of **Group B Streptococcus** (*Streptococcus agalactiae*), not pneumococcus. - *S. agalactiae* typically causes infections in **neonates** or postpartum women, rather than lobar pneumonia with rust-colored sputum. *C. Coagulase test and catalase test* - The **catalase test** is the primary step to differentiate *Staphylococci* (positive) from *Streptococci* (negative). - The **coagulase test** specifically identifies *Staphylococcus aureus*, which would appear as **clusters** on Gram stain rather than pairs. *D. Oxidase test and motility in SIM medium* - These tests are generally used for identifying **Gram-negative bacilli** like *Pseudomonas aeruginosa* or *Enterobacteriaceae*. - *Streptococcus pneumoniae* is a **Gram-positive** non-motile coccus and would not be evaluated using these biochemical parameters.

Q: Which of the following causes mesenteric lymphadenitis?

All of the above. **Explanation:** Mesenteric lymphadenitis is the inflammation of the lymph nodes within the mesentery, often clinically mimicking acute appendicitis (Pseudo-appendicitis syndrome). This condition is caused by a variety of infectious agents, including viral, bacterial, and parasitic pathogens. * **Yersinia pseudotuberculosis (and Y. enterocolitica):** These are the most classic bacterial causes. They have a tropism for lymphoid tissue and frequently cause terminal ileitis and mesenteric lymphadenitis, leading to right lower quadrant pain. * **Campylobacter jejuni:** While primarily known for causing inflammatory diarrhea, *Campylobacter* can also involve the mesenteric lymph nodes, presenting with a clinical picture indistinguishable from appendicitis. * **Adenovirus:** This is the most common **viral** cause of mesenteric lymphadenitis, particularly in children. It is often associated with a concurrent or recent upper respiratory tract infection. Since all three agents listed are recognized causes of this clinical syndrome, **Option D (All of the above)** is the correct answer. **High-Yield Clinical Pearls for NEET-PG:** * **Pseudo-appendicitis:** Always consider *Yersinia enterocolitica* or *Yersinia pseudotuberculosis* in a patient presenting with appendicitis-like symptoms but a normal appendix on imaging/surgery. * **Diagnosis:** Ultrasound is the preferred initial imaging modality, showing enlarged lymph nodes (>8mm in short-axis diameter) with a normal-looking appendix. * **Other Causes:** *Salmonella typhi*, *Mycobacterium tuberculosis* (Tabes mesenterica), and Giardiasis can also lead to mesenteric nodal enlargement. * **Key Distinction:** Unlike acute appendicitis, mesenteric lymphadenitis is usually self-limiting and managed conservatively.

Q: A 45-year-old man with AIDS presents with productive cough, fever, and night sweats. Chest X-ray reveals an ill-defined area of consolidation at the periphery of the right middle lobe and mediastinal lymphadenopathy. Sputum culture yields acid-fast bacilli. The patient subsequently develops severe headache and neck rigidity. Which of the following brain areas is most likely affected by this patient's infection?

Base of the brain. **Explanation:** The clinical presentation of productive cough, fever, night sweats, and acid-fast bacilli in sputum in an immunocompromised patient (AIDS) strongly suggests **Tuberculosis (TB)**. The subsequent development of headache and neck rigidity indicates **Tuberculous Meningitis (TBM)**, a common extrapulmonary complication in HIV-infected individuals. **1. Why "Base of the brain" is correct:** Tuberculous meningitis is characterized by a thick, gelatinous **exudate** that preferentially accumulates in the **basal cisterns** (interpeduncular fossa, pontine cistern, and around the optic chiasm). This basal distribution occurs because the bacilli spread via the subarachnoid space after the rupture of a subependymal tubercle (Rich focus). This predilection for the base of the brain often leads to cranial nerve palsies (CN III, IV, and VI) and obstructive hydrocephalus. **2. Why other options are incorrect:** * **Cerebellum:** While tuberculomas can occur here, it is not the primary site for the characteristic meningeal exudate. * **Hippocampus:** Classically associated with **Herpes Simplex Virus (HSV-1) encephalitis** or Rabies (Negri bodies), not TB. * **Periventricular white matter:** This is the characteristic site for **Progressive Multifocal Leukoencephalopathy (PML)** caused by the JC virus or Primary CNS Lymphoma in AIDS patients. **Clinical Pearls for NEET-PG:** * **Rich Focus:** A small tuberculous lesion in the brain parenchyma or meninges that ruptures into the subarachnoid space to cause TBM. * **CSF Findings in TBM:** High protein, very low glucose, and **lymphocytic pleocytosis** (Cobweb coagulum formation). * **Imaging:** Contrast-enhanced CT/MRI typically shows **basal meningeal enhancement**. * **Complication:** The most common cranial nerve involved in TBM is the **6th Nerve (Abducens)**.

Q: Which of the following is NOT true about cutaneous anthrax?

It is extremely painful.. Cutaneous anthrax, caused by *Bacillus anthracis*, is the most common clinical form of the disease. Understanding its classic presentation is vital for NEET-PG. **Why Option A is the correct answer (The "Not True" statement):** The hallmark of a cutaneous anthrax lesion is that it is **painless**. Despite its angry, necrotic appearance, the lesion lacks significant pain or tenderness. If a similar-looking lesion is exquisitely painful, a clinician should instead suspect a staphylococcal carbuncle or orf. **Analysis of other options:** * **Option B:** The lesion is typically surrounded by extensive **non-pitting edema** and congestion. This is due to the "Edema Factor" (EF), a component of the anthrax toxin that increases cAMP levels, leading to massive fluid accumulation in the extracellular space. * **Option C:** The lesion begins as a papule, progresses to a vesicle, and eventually undergoes central necrosis to form a characteristic **painless black eschar** (malignant pustule) with a surrounding rim of edema. * **Option D:** While the primary lesion is localized, **satellite vesicles** or nodules may occasionally develop. Regional lymphadenopathy (e.g., inguinal or axillary, depending on the site of inoculation) is common and may be associated with systemic symptoms. **High-Yield Clinical Pearls for NEET-PG:** 1. **Occupational Hazard:** Often called "Hide-porter’s disease" because it affects those handling infected animal products. 2. **Microscopy:** *B. anthracis* shows a "Bamboo stick" appearance and "Medusa head" colonies on agar. 3. **McFadyean’s Reaction:** Used to visualize the capsule (polypeptide of D-glutamic acid) using polychrome methylene blue. 4. **String of Pearls Reaction:** Occurs when grown on agar containing penicillin.

Q: Which infection is not common in HIV patients?

Aspergillosis. ### Explanation The correct answer is **Aspergillosis**. **1. Why Aspergillosis is the correct answer:** While *Aspergillus* is an opportunistic fungus, it is primarily seen in patients with **severe neutropenia** (e.g., leukemia, bone marrow transplant) or those on high-dose corticosteroids. In HIV/AIDS patients, the primary immune deficit is **Cell-Mediated Immunity (CD4+ T-cell depletion)** rather than neutrophil dysfunction. Therefore, unless an HIV patient is also neutropenic or has advanced structural lung disease, invasive aspergillosis is significantly less common compared to the other listed infections. **2. Why the other options are incorrect:** * **Cryptosporidiosis (Option A):** This is a classic AIDS-defining illness. It causes chronic, profuse watery diarrhea in patients with CD4 counts typically below 100 cells/mm³. * **Atypical Mycobacterial Infection (Option B):** Specifically *Mycobacterium avium complex* (MAC), this is very common in late-stage AIDS (CD4 < 50 cells/mm³), presenting as disseminated disease with fever and lymphadenopathy. * **Candidiasis (Option D):** Oropharyngeal candidiasis (thrush) is the most common opportunistic fungal infection in HIV patients and often serves as an early clinical sign of disease progression. **3. NEET-PG High-Yield Pearls:** * **Most common fungal infection in HIV:** Candidiasis (Mucosal). * **Most common opportunistic infection (overall) in HIV:** *Pneumocystis jirovecii* pneumonia (PCP). * **Most common CNS mass lesion in HIV:** Toxoplasmosis. * **Aspergillus Risk Factor:** Remember "Neutropenia" for *Aspergillus* and "CD4 count" for the others. * **Diagnostic Clue:** *Aspergillus* shows septate hyphae with acute-angle (45°) branching.

Question 1

A patient presents with a painless genital ulcer followed by painful inguinal buboes (lymphadenopathy). Which strains of Chlamydia trachomatis are responsible for this condition?

Accepted Answer

L1–L3

Answer

A, B, C

Answer

D–K

Answer

B, C, D

Question 2

A female presents with high grade fever, diffuse erythematous rash and hypotension. She is
currently menstruating and using tampoons. The toxin responsible acts by?

Accepted Answer

Vbeta region of the T-cell receptor and MHC class II molecule

Answer

MHC class I molecule only

Answer

CD4 receptor only

Answer

B-cell receptor and IgG

Question 3

A 32-year-old woman with a history of splenectomy presents to the emergency department with
sudden-onset high-grade fever, vomiting, hypotension, and rapidly progressive septic shock. Her
symptoms began 2 weeks after a minor febrile illness. Which organism is the most likely causative
agent of this life-threatening condition?

Accepted Answer

Streptococcus pneumoniae

Answer

Escherichia coli

Answer

Staphylococcus aureus

Answer

Pseudomonas aeruginosa

Question 4

A 34-year-old man with a CD4 count of 48 cells/µL presents with a 3-week history of progressive headache, low-grade fever, and neck stiffness. Lumbar puncture reveals elevated opening pressure, low glucose, and elevated protein. CSF microscopy is shown (Image 1). Which of the following best describes the virulence mechanism of the organism identified that directly enables its evasion of phagocytic killing in the host?

Accepted Answer

A. Production of a polysaccharide capsule that inhibits complement-mediated opsonisation and phagocytosis

Answer

D. Expression of protein A on the cell wall that binds the Fc region of IgG and prevents opsonin recognition

Answer

B. Formation of a heat-stable lipopolysaccharide that activates TLR-4 and suppresses macrophage oxidative burst

Answer

C. Secretion of a pore-forming exotoxin that lyses neutrophils before phagocytic engulfment occurs

Question 5

A 65-year-old diabetic male presents with high-grade fever, productive rust-coloured sputum, and right-sided pleuritic chest pain for 3 days. His oxygen saturation is 88% on room air. A sputum Gram stain is performed (Image 1). Which of the following tests would most definitively confirm the identity of this organism from a positive blood culture?

Accepted Answer

A. Optochin sensitivity and bile solubility

Answer

B. CAMP test and hippurate hydrolysis

Answer

C. Coagulase test and catalase test

Answer

D. Oxidase test and motility in SIM medium

Question 6

Which of the following is NOT implicated in congenital transmission?

Accepted Answer

Hepatitis A

Answer

Toxoplasmosis

Answer

Herpes

Answer

Syphilis

Question 7

Which of the following causes mesenteric lymphadenitis?

Accepted Answer

All of the above

Answer

Adenovirus

Answer

Campylobacter

Answer

Yersinia pseudotuberculosis

Question 8

A 45-year-old man with AIDS presents with productive cough, fever, and night sweats. Chest X-ray reveals an ill-defined area of consolidation at the periphery of the right middle lobe and mediastinal lymphadenopathy. Sputum culture yields acid-fast bacilli. The patient subsequently develops severe headache and neck rigidity. Which of the following brain areas is most likely affected by this patient's infection?

Accepted Answer

Base of the brain

Answer

Cerebellum

Answer

Hippocampus

Answer

Periventricular white matter

Question 9

Which of the following is NOT true about cutaneous anthrax?

Accepted Answer

It is extremely painful.

Answer

The entire affected area is congested and edematous.

Answer

It presents with central crustation and a black eschar.

Answer

Satellite nodules may appear around the inguinal region.

Question 10

Which infection is not common in HIV patients?

Accepted Answer

Aspergillosis

Answer

Cryptosporidiosis

Answer

Atypical mycobacterial infection

Answer

Candidiasis

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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