Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 221: What is the drug of choice for the treatment of neurosyphilis?

A. Benzathine Penicillin G
B. Procaine Penicillin G (Correct Answer)
C. Penicillin V
D. Tetracycline

Explanation: The treatment of neurosyphilis requires a penicillin formulation that can achieve high, sustained therapeutic concentrations in the cerebrospinal fluid (CSF). [1] **1. Why Procaine Penicillin G is Correct:** According to standard treatment guidelines (CDC/WHO), the preferred treatment for neurosyphilis is **Aqueous Crystalline Penicillin G** (18–24 million units per day, administered intravenously). However, if IV access is unavailable or compliance is an issue, the alternative is **Procaine Penicillin G** (2.4 million units IM once daily) plus **Probenecid** (500 mg orally four times daily) for 10–14 days. [1] In the context of the provided options, Procaine Penicillin is the only formulation capable of reaching the necessary CSF levels when combined with Probenecid. [1] **2. Why Other Options are Incorrect:** * **Benzathine Penicillin G:** This is the drug of choice for primary, secondary, and early latent syphilis. However, it is a long-acting formulation that provides very low serum levels and **does not penetrate the blood-brain barrier** sufficiently to treat neurosyphilis. * **Penicillin V:** This is an oral formulation with poor bioavailability and negligible CNS penetration; it has no role in the treatment of syphilis. * **Tetracycline:** While Doxycycline (a tetracycline) can be used as an alternative in penicillin-allergic patients for early syphilis, it is not the first-line choice for neurosyphilis. Ceftriaxone is the preferred alternative if penicillin cannot be used for neurosyphilis. **Clinical Pearls for NEET-PG:** * **Jarisch-Herxheimer Reaction:** A common acute febrile reaction occurring within 24 hours of starting syphilis treatment due to the release of endotoxins from dying spirochetes. * **Argyll Robertson Pupil:** A classic sign of neurosyphilis (Tabes Dorsalis) where the pupil accommodates but does not react to light ("Prostitute's Pupil"). * **Gold Standard Diagnosis:** CSF-VDRL is highly specific for neurosyphilis, though its sensitivity is lower.

Question 222: A girl complained of abdominal pain with the passage of foul-smelling stool that does not wash away easily. There is a history of swimming in contaminated water. What is the likely causative organism?

A. Giardia lamblia (Correct Answer)
B. Naegleria
C. Amoeba
D. Shigella

Explanation: The clinical presentation described is a classic case of **Giardiasis**, caused by the flagellated protozoan **Giardia lamblia**. **Why Giardia lamblia is correct:** The hallmark of Giardiasis is **steatorrhea** (fatty, foul-smelling stools that float and are difficult to flush/wash away). This occurs because the parasite attaches to the duodenal and jejunal mucosa via a ventral sucking disc, causing blunting of villi and malabsorption of fats. The history of **swimming in contaminated water** (lakes, streams, or pools) is a high-yield risk factor, as Giardia cysts are resistant to standard chlorine levels [1]. **Why the other options are incorrect:** * **Naegleria fowleri:** Known as the "brain-eating amoeba," it is also associated with contaminated water but causes Primary Amoebic Meningoencephalitis (PAM), not gastrointestinal symptoms. * **Amoeba (Entamoeba histolytica):** Causes amoebic dysentery characterized by bloody stools (haematochezia) and flask-shaped ulcers. It does not typically cause steatorrhea [2]. * **Shigella:** A bacterial cause of inflammatory diarrhea (dysentery). It presents with high fever, tenesmus, and stools containing blood and mucus, rather than foul-smelling, fatty stools. **High-Yield Clinical Pearls for NEET-PG:** * **Site of infection:** Primarily the **Duodenum** and upper Jejunum (Giardia "likes" the alkaline environment) [1]. * **Diagnosis:** Stool microscopy (cysts or pear-shaped trophozoites with "falling leaf" motility). **Entero-test (String test)** can be used if stool samples are negative. * **Drug of Choice:** **Tinidazole** (preferred over Metronidazole due to single-dose efficacy). * **Common Association:** Increased incidence in patients with **IgA deficiency**.

Question 223: All of the following are associated with primary tuberculosis EXCEPT:

A. Cavitary lesion (Correct Answer)
B. Pleural effusion
C. Fibrocaseous lesion
D. Phlyctenular conjunctivitis

Explanation: **Explanation:** The distinction between primary and secondary (reactivation) tuberculosis is a frequent high-yield topic in NEET-PG. **Why "Cavitary lesion" is the correct answer:** Cavitary lesions are the hallmark of **Secondary (Post-primary) Tuberculosis** [3]. Cavitation occurs due to a robust cell-mediated immune response (Type IV hypersensitivity) leading to extensive tissue necrosis. In contrast, **Primary TB** typically presents as a localized parenchymal lesion (Ghon focus) with associated lymphadenopathy (Ghon complex) [1], but rarely results in cavitation because the initial immune response is usually insufficient to cause such extensive tissue destruction. **Analysis of incorrect options:** * **Pleural effusion:** This is a common manifestation of primary TB, often resulting from the rupture of a subpleural focus into the pleural space. * **Fibrocaseous lesion:** Primary TB begins with a Ghon focus, which is pathologically a fibrocaseous granuloma [1]. While secondary TB also shows caseation, it is a fundamental feature of the primary infection as the body attempts to wall off the bacilli. * **Phlyctenular conjunctivitis:** This is a known **hypersensitivity reaction** to the tubercle bacilli protein [2]. It is considered a "delayed-type hypersensitivity" manifestation that can occur during the primary infection stage. **High-Yield Clinical Pearls for NEET-PG:** * **Ghon Complex:** Parenchymal lesion + Lymphangitis + Hilar lymphadenopathy [1]. * **Ranke Complex:** A healed, calcified Ghon complex (visible on X-ray) [1]. * **Location:** Primary TB usually affects the **lower or middle lobes**, whereas Secondary TB favors the **apical/posterior segments of the upper lobes** (due to higher oxygen tension). * **Epithelioid cells:** These are modified macrophages and are the characteristic diagnostic cell type found in TB granulomas [1].

Question 224: The appearance of this foot is most consistent with which one of the following diagnoses?

A. Buruli ulcer
B. Chromomycosis (Correct Answer)
C. Leishmaniasis
D. Madura foot

Explanation: ***Chromomycosis*** - Characterized by **verrucous, cauliflower-like lesions** on the foot, caused by dematiaceous fungi like **Fonsecaea pedrosoi** or **Cladophialophora carrionii**. - Diagnosis confirmed by finding **sclerotic bodies** (muriform cells) in tissue or KOH preparations, showing thick-walled, brown, septate cells. *Buruli ulcer* - Presents as **painless, necrotic ulcers** with undermined edges, not verrucous lesions, caused by **Mycobacterium ulcerans**. - Typically occurs in **tropical regions** near water bodies and progresses from nodules to large ulcerative lesions. *Leishmaniasis* - **Cutaneous leishmaniasis** presents as painless ulcers with **raised, indurated borders**, not cauliflower-like growths. - Caused by **Leishmania species** transmitted by **sandfly bites**, diagnosed by finding amastigotes in tissue samples. *Madura foot* - **Mycetoma** characterized by the triad of **tumefaction, sinuses, and grains** discharging from multiple openings. - Caused by either **actinomycetes** (actinomycetoma) or **true fungi** (eumycetoma), with grains varying in color depending on the causative organism.

Question 225: Which statement is FALSE regarding Tuberculosis in an HIV-positive individual?

A. Frequent negative sputum smear.
B. False negative tuberculin test result.
C. Extrapulmonary tuberculosis is more common.
D. Cavitation lesions in the lungs as shown by chest X-ray. (Correct Answer)

Explanation: **Explanation:** The presentation of Tuberculosis (TB) in HIV-positive patients is heavily dependent on the degree of immunosuppression (CD4 count). **Why Option D is the Correct (False) Statement:** Cavitation is a result of a robust cell-mediated immune response where the body attempts to wall off the infection, leading to caseous necrosis and tissue destruction. In HIV-positive individuals, especially those with low CD4 counts, the immune system is too weak to mount this hypersensitivity response. Consequently, **atypical chest X-ray findings** are common; patients often show lower lobe infiltrates, hilar lymphadenopathy, or even normal X-rays, while **cavitation is characteristically absent.** **Analysis of Other Options:** * **Option A (True):** Sputum smears are frequently negative because the lack of cavitation means fewer bacilli are discharged into the airways. * **Option B (True):** The Tuberculin Skin Test (TST/Mantoux) relies on a Delayed-Type Hypersensitivity (DTH) response. Due to T-cell depletion in HIV, patients often exhibit **anergy**, leading to false-negative results. * **Option C (True):** As immunity declines, the body fails to contain the primary infection, leading to hematogenous spread. This results in a much higher incidence of extrapulmonary (e.g., lymph nodes, CNS) and disseminated (miliary) TB. **NEET-PG High-Yield Pearls:** 1. **Diagnosis:** Since smear microscopy is often negative, **CBNAAT (GeneXpert)** is the preferred initial diagnostic test for TB in HIV patients. 2. **IRIS:** Starting ART in a TB patient can lead to **Immune Reconstitution Inflammatory Syndrome**, where the recovering immune system causes an exaggerated inflammatory response to TB antigens. 3. **Treatment:** Rifampicin is a potent inducer of CYP450; therefore, Efavirenz is the preferred NNRTI as it has fewer interactions compared to Protease Inhibitors.

Question 226: A patient with HIV and a CD4 count of 160 cells/µL presents with fever, cough, and shortness of breath for 3 weeks. Chest X-ray and silver staining of bronchoalveolar lavage are shown. What is the drug of choice for the causative organism?

A. Azithromycin
B. Vancomycin
C. Gentamicin
D. Cotrimoxazole (Correct Answer)

Explanation: ***Cotrimoxazole*** - The clinical picture of **HIV patient** with **CD4 <200 cells/µL**, subacute respiratory symptoms, and **silver staining** showing characteristic **Pneumocystis jirovecii cysts** in BAL confirms **Pneumocystis pneumonia (PCP)**. - **Cotrimoxazole (TMP-SMX)** is the **first-line drug of choice** for both treatment and prophylaxis of PCP in immunocompromised patients. *Azithromycin* - This **macrolide antibiotic** is effective against **atypical bacteria** like Mycoplasma and Chlamydia, but has **no activity against Pneumocystis jirovecii**. - Commonly used for **community-acquired pneumonia** and **MAC prophylaxis** in HIV patients, but not for PCP treatment. *Vancomycin* - This **glycopeptide antibiotic** is specifically used for **gram-positive bacterial infections**, particularly **MRSA** and other resistant organisms. - Has **no antifungal activity** and is ineffective against **Pneumocystis jirovecii**, which is a fungal pathogen. *Gentamicin* - This **aminoglycoside antibiotic** is primarily effective against **gram-negative bacteria** and some gram-positive organisms. - Has **no antifungal properties** and would be completely ineffective against **Pneumocystis jirovecii** pneumonia.

Question 227: Sardonic grin is associated with which condition?

A. Rabies
B. Tetanus (Correct Answer)
C. Bell's palsy
D. Hemiplegia

Explanation: **Explanation:** **Risus sardonicus** (Sardonic grin) is a characteristic clinical sign of **Tetanus**, caused by the neurotoxin *tetanospasmin* produced by *Clostridium tetani* [2]. **Why Tetanus is correct:** Tetanospasmin blocks the release of inhibitory neurotransmitters (GABA and Glycine) from Renshaw cells in the spinal cord. This leads to unchecked excitatory impulses, resulting in generalized muscle rigidity and spasms. The "sardonic grin" occurs due to the sustained contraction (spasticity) of the facial muscles, particularly the **frontalis** (raising the eyebrows) and the **orbicularis oris** (retracting the corners of the mouth). Strychnine poisoning, which also affects Renshaw cells and glycine inhibition, can produce a similar presentation of constant muscle contractions [1]. **Why other options are incorrect:** * **Rabies:** Characterized by hydrophobia, aerophobia, and "furious" episodes due to encephalitis, but it does not typically present with sustained facial muscle spasms. * **Bell’s Palsy:** This is a lower motor neuron lesion of the facial nerve (CN VII) resulting in facial **paralysis** (flaccidity), not spastic contraction. * **Hemiplegia:** Usually results from an upper motor neuron lesion (like a stroke), causing contralateral weakness or paralysis of the limbs and lower face, rather than a bilateral sardonic expression. **High-Yield Clinical Pearls for NEET-PG:** * **Trismus (Lockjaw):** Usually the earliest presenting symptom of tetanus (contraction of masseter muscles). * **Opisthotonus:** Severe backward arching of the spine due to extensor spasm. * **Management:** Neutralize unbound toxin with Human Tetanus Immunoglobulin (HTIG), wound debridement, and Metronidazole (preferred over Penicillin as Penicillin is a GABA antagonist) [2]. * **Autonomic Instability:** A common cause of death in modern ICU settings.

Question 228: In a neutropenic patient, which of the following would be most commonly encountered as a cause of bacterial meningitis and brain abscess?

A. Pseudomonas aeruginosa (Correct Answer)
B. Staphylococcus aureus
C. Haemophilus influenzae
D. Bacteroides fragilis

Explanation: ### Explanation **1. Why Pseudomonas aeruginosa is the correct answer:** Neutropenia (Absolute Neutrophil Count <500 cells/mm³) is a critical risk factor for life-threatening infections. In these patients, the integrity of mucosal barriers is often compromised, and the lack of phagocytic cells allows opportunistic pathogens to disseminate [1]. **Pseudomonas aeruginosa** is a quintessential opportunistic gram-negative rod that thrives in neutropenic environments. It has a unique predilection for invading blood vessel walls (*ecthyma gangrenosum*), leading to hematogenous spread to the Central Nervous System (CNS). This results in aggressive bacterial meningitis and a high propensity for forming brain abscesses compared to other common pathogens in this specific population [1]. **2. Analysis of Incorrect Options:** * **Staphylococcus aureus (Option B):** While a common cause of skin infections and endocarditis-related brain abscesses, it is less specifically associated with the unique vulnerability of the neutropenic state compared to *Pseudomonas*. * **Haemophilus influenzae (Option C):** This is a classic cause of meningitis in children or unvaccinated individuals. However, its incidence has significantly decreased due to the Hib vaccine, and it is not the primary pathogen associated with neutropenia. * **Bacteroides fragilis (Option D):** This anaerobe is typically associated with brain abscesses secondary to chronic otitis media or intra-abdominal sepsis, but it is not the most common cause in the context of systemic neutropenia. **3. Clinical Pearls for NEET-PG:** * **The "Big Three" in Neutropenia:** Always prioritize *Pseudomonas aeruginosa*, *Enterobacteriaceae*, and *Staphylococci* [1]. * **Fungal Consideration:** If a neutropenic patient with CNS symptoms does not respond to antibacterial therapy, suspect **Aspergillus** (which also causes angioinvasive brain abscesses). * **Empiric Choice:** For febrile neutropenia, the initial antibiotic must cover *Pseudomonas* (e.g., Piperacillin-Tazobactam, Cefepime, or Meropenem) [1]. * **Key Association:** *Pseudomonas* + Neutropenia + Skin Lesion = **Ecthyma Gangrenosum**.

Question 229: Salmonellosis is most commonly associated with which of the following conditions?

A. Sickle cell anemia (Correct Answer)
B. Thalassemia
C. Hemophilia
D. Cystic fibrosis

Explanation: **Explanation:** The association between **Sickle Cell Anemia (SCA)** and **Salmonellosis** (specifically *Salmonella* osteomyelitis) is a classic high-yield medical concept. Patients with SCA are uniquely predisposed to *Salmonella* infections due to several pathophysiological mechanisms: 1. **Autosplenectomy:** Chronic sickling leads to splenic infarction and functional asplenia, impairing the clearance of encapsulated organisms and *Salmonella* [1]. 2. **Bowel Infarction:** Microvascular occlusion in the gut wall allows *Salmonella* (part of the normal flora in some) to translocate into the bloodstream. 3. **Expanded Bone Marrow:** Chronic hemolysis leads to marrow hyperplasia and sluggish blood flow, creating a nidus for bacterial seeding. 4. **Impaired Macrophage Function:** The Reticuloendothelial System (RES) is "overloaded" with the breakdown products of sickled RBCs, reducing its ability to phagocytose bacteria. **Analysis of Incorrect Options:** * **B. Thalassemia:** While these patients are at risk for infections due to iron overload (siderophilic bacteria like *Yersinia*) and splenectomy, the specific association with *Salmonella* is significantly weaker than in SCA. * **C. Hemophilia:** This is a coagulation disorder. Risk of infection is primarily related to blood-borne pathogens (HIV, Hepatitis) from historical transfusion practices, not *Salmonella*. * **D. Cystic Fibrosis:** These patients are predisposed to pulmonary infections, most notably *Pseudomonas aeruginosa* and *Staphylococcus aureus*, not systemic Salmonellosis. **Clinical Pearls for NEET-PG:** * **Most common cause of Osteomyelitis in SCA:** While *Staphylococcus aureus* is the most common cause of osteomyelitis in the general population, **Salmonella** is uniquely frequent and often cited as the most common or second most common cause specifically in SCA patients [2]. * **Drug of Choice:** Third-generation cephalosporins (e.g., Ceftriaxone) or Fluoroquinolones are typically used for treatment. * **X-ray finding:** Look for "diaphyseal involvement" in *Salmonella* osteomyelitis.

Question 230: Leukopenia is characteristic of which of the following conditions?

A. Appendicitis
B. Enteric fever (Correct Answer)
C. Meningitis
D. Myocardial infarction

Explanation: **Explanation:** **Correct Answer: B. Enteric fever** Leukopenia (a decrease in the total white blood cell count) is a classic hematological hallmark of **Enteric Fever (Typhoid)** caused by *Salmonella Typhi* [1]. While most bacterial infections trigger neutrophilic leukocytosis, Enteric fever is a notable exception [1]. The underlying mechanism involves the invasion of the Reticuloendothelial System (RES), specifically the bone marrow, where the bacteria cause marrow suppression and increased destruction of cells. Typically, the WBC count ranges between 3,000 to 5,000/mm³. **Analysis of Incorrect Options:** * **A. Appendicitis:** This is an acute pyogenic inflammatory condition. It characteristically presents with **leukocytosis** (elevated WBC) with a "shift to the left" (increased immature neutrophils), which helps in clinical diagnosis. * **C. Meningitis:** Acute bacterial meningitis typically presents with significant **polymorphonuclear leukocytosis** as the body mounts an immune response against the invading pathogen (e.g., *S. pneumoniae* or *N. meningitidis*). * **D. Myocardial Infarction:** Tissue necrosis in MI triggers a systemic inflammatory response, leading to a transient **leukocytosis** (usually appearing within 24 hours), not leukopenia. **High-Yield Clinical Pearls for NEET-PG:** * **Relative Bradycardia (Faget’s Sign):** Another classic feature of Enteric fever where the pulse rate is slower than expected for the degree of fever [1]. * **Other causes of Leukopenia in Infections:** Viral infections (Influenza, Measles, Hepatitis), Malaria, Kala-azar, and Brucellosis [2]. * **Diagnostic Gold Standard:** Bone marrow culture is the most sensitive test for Enteric fever, especially if antibiotics have already been started. Blood culture is most sensitive in the first week.

Practice by Chapter

Principles of Antimicrobial Therapy

Practice Questions

Fever of Unknown Origin

Practice Questions

HIV/AIDS and Related Infections

Practice Questions

Tuberculosis and Mycobacterial Diseases

Practice Questions

Tropical and Parasitic Infections

Practice Questions

Viral Infections (Hepatitis, Herpes, etc.)

Practice Questions

Healthcare-Associated Infections

Practice Questions

Fungal Infections

Practice Questions

Sepsis and Septic Shock

Practice Questions

Infection in Immunocompromised Hosts

Practice Questions

Emerging and Re-emerging Infections

Practice Questions

Antimicrobial Resistance

Practice Questions

Vaccination Principles

Practice Questions

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