Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 701: A 40-year-old diabetic patient presents with proptosis of one eye and a black eschar over the palate. What is the likely causative organism?

A. Pseudomonas
B. Candida
C. E. coli
D. Mucor (Correct Answer)

Explanation: ### Explanation The clinical presentation of **proptosis** and a **black necrotic eschar** on the palate in a **diabetic patient** (especially one in ketoacidosis) is the classic triad for **Rhinocerebral Mucormycosis** [1]. **Why Mucor is the correct answer:** Mucormycosis is caused by fungi of the order Mucorales (e.g., *Rhizopus*, *Mucor*). These fungi are **angioinvasive**, meaning they invade blood vessel walls, leading to thrombosis, tissue ischemia, and necrosis [1]. This necrosis manifests clinically as a characteristic **black eschar** on the nasal mucosa or palate. The infection spreads rapidly from the sinuses to the orbit (causing proptosis and ophthalmoplegia) and eventually to the brain. **Why the other options are incorrect:** * **Pseudomonas:** While it can cause "Malignant Otitis Externa" in diabetics (involving the ear canal and skull base), it does not typically present with a palatal eschar or acute rhino-orbital syndrome. * **Candida:** Usually causes superficial infections like oral thrush (white plaques) or systemic candidiasis. It is not angioinvasive enough to cause rapid tissue necrosis and eschar formation [2]. * **E. coli:** A common cause of urinary tract infections and sepsis in diabetics, but it does not have a predilection for the paranasal sinuses or cause necrotic facial lesions. **High-Yield Clinical Pearls for NEET-PG:** * **Risk Factors:** Uncontrolled Diabetes Mellitus (Ketoacidosis), Neutropenia, and Iron overload (Deferoxamine use) [1]. * **Diagnosis:** KOH mount or biopsy showing **broad, ribbon-like, non-septate hyphae** with **right-angle (90°) branching**. * **Management:** Immediate surgical debridement + Intravenous **Liposomal Amphotericin B** [1]. (Note: Azoles like Fluconazole are ineffective; Posaconazole/Isavuconazole are alternatives).

Question 702: What are the investigations in a clinically suspected case of tuberculosis?

A. Mantoux test (in children)
B. Sputum for Acid-Fast Bacilli (AFB)
C. Bactec culture
D. All of the above (Correct Answer)

Explanation: In clinical practice, the diagnosis of Tuberculosis (TB) relies on a combination of immunological screening, microbiological identification, and advanced culture techniques. **Explanation of the Correct Answer:** The correct answer is **D (All of the above)** because each investigation plays a specific role in the diagnostic algorithm: * **Mantoux Test (Option A):** While it cannot differentiate between latent infection and active disease, it is a vital screening tool, especially in children (pediatric TB) [1]. A positive result (usually $\geq 10$ mm induration) indicates a Type IV hypersensitivity reaction to Tuberculin Purified Protein Derivative (PPD). * **Sputum for AFB (Option B):** This remains the traditional "gold standard" for initial diagnosis and assessing infectivity [1]. Using Ziehl-Neelsen (ZN) staining, a minimum of 5,000–10,000 bacilli/ml is required for a positive result [1]. * **Bactec Culture (Option C):** This is a rapid automated liquid culture system (radiometric). Unlike traditional Lowenstein-Jensen (LJ) medium, which takes 6–8 weeks, Bactec can provide results in 7–14 days, allowing for faster diagnosis and drug susceptibility testing (DST). **High-Yield Clinical Pearls for NEET-PG:** * **CBNAAT (GeneXpert):** Currently the preferred initial diagnostic test under the NTEP (National TB Elimination Program) due to its high sensitivity and ability to detect Rifampicin resistance within 2 hours. * **Sputum Collection:** Two samples are required (one "spot" and one "early morning"). * **Culture:** Liquid culture (MGIT/Bactec) is more sensitive and faster than solid culture (LJ Medium). * **Gold Standard:** While culture is the microbiological gold standard, CBNAAT is the frontline investigation in the current Indian protocol.

Question 703: A 20-year-old male was admitted with fever, headache and retro-orbital pain with rash. The tourniquet test is positive. What is the diagnosis?

A. Dengue hemorrhagic fever (Correct Answer)
B. Malaria
C. Japanese encephalitis
D. Measles

Explanation: ***Dengue hemorrhagic fever***- The combination of high fever, **headache**, **retro-orbital pain**, and rash is characteristic of classic Dengue fever (breakbone fever) [1].- A **positive tourniquet test** suggests increased capillary fragility, which, along with the other symptoms, strongly indicates progression toward **Dengue hemorrhagic fever (DHF)** [1].*Malaria*- Malaria is characterized by cyclical fever patterns (such as tertian or quartan), often associated with severe chills and sweats, which are not mentioned here.- It typically does not cause prominent retro-orbital pain or lead to a positive **tourniquet test** as a primary finding.*Measles*- Measles is typically preceded by a prodrome including cough, coryza, and conjunctivitis, followed by the appearance of **Koplik spots** (buccal lesions).- The rash starts on the face and spreads downwards, and while fever is present, the key combination of **retro-orbital pain** and a positive tourniquet test is not characteristic.*Japanese encephalitis*- This is primarily a **neuroinvasive disease** transmitted by Culex mosquitoes, leading to symptoms like altered mental status, seizures, and focal neurological deficits.- Simple fever, headache, and rash without significant encephalopathy make this diagnosis less likely, and it is not typically associated with the **tourniquet test**.

Question 704: An AIDS-positive patient came with a history of fever, vomiting, and meningismus. Which of the following tests help in the rapid diagnosis of cryptococcal meningitis?

A. CSF culture
B. India ink preparation of CSF
C. Urine lateral flow assay for cryptococcal antigen (Correct Answer)
D. Blood culture

Explanation: ***Urine lateral flow assay for cryptococcal antigen*** - The **Cryptococcal Antigen (CrAg) lateral flow assay (LFA)**, performed on various body fluids (CSF, serum, or urine), allows for rapid diagnosis, often yielding results in 10 minutes. - Detection of CrAg is highly sensitive in patients with extensive disease, such as those with AIDS and high fungal burdens, facilitating quick initiation of life-saving antifungal therapy. *India ink preparation of CSF* - Although relatively quick, the **India ink preparation** has low sensitivity (50-75%) in HIV-associated cryptococcal meningitis, leading to potential false-negative results. - This test identifies the yeast by visualizing the characteristic **capsule** against a black background, but its utility has largely been replaced by the more sensitive CrAg assay. *Blood culture* - Blood cultures confirm **cryptococcemia** (disseminated infection), which is common in AIDS patients with meningitis, but require several days (3–7 or more) for growth and identification. - Due to the prolonged incubation time, blood culture is unsuitable for the **rapid diagnosis** required to manage acute meningeal symptoms promptly. *CSF culture* - CSF culture remains the **gold standard** for definitive diagnosis, confirmation of viability, and performance of antifungal susceptibility testing. - Similar to blood culture, CSF culture takes multiple days (typically 2–7 days) to provide results, thus delaying immediate treatment needed for **meningitis**.

Question 705: A woman presents with sudden-onset high-grade fever, hypotension, diffuse rash, and a history of using a tampon for an extended period. What is the most likely diagnosis?

A. Septic shock
B. Pelvic Inflammatory Disease
C. Toxic Shock Syndrome (Correct Answer)
D. Streptococcal pharyngitis

Explanation: Toxic Shock Syndrome - This diagnosis is defined by the sudden onset of **high fever**, **hypotension** (shock), and a **diffuse erythematous rash** (often described as sunburn-like), strongly supported by the history of prolonged **tampon use** (a common source for *Staphylococcus aureus* producing **TSST-1** superantigen). [1] - TSS is a life-threatening illness caused by toxins that induce massive cytokine release, leading rapidly to shock and potential multi-organ failure. [1] Septic shock - While TSS is a specific diagnosis within the broader category of **sepsis/septic shock**, the acute presentation with the classic **diffuse rash** and clear association with prolonged tampon use makes TSS the most accurate diagnosis. - Septic shock is a general condition of infection-induced circulatory failure but lacks the specific **sunburn-like rash** and classic toxin etiology that defines TSS. Pelvic Inflammatory Disease - PID typically presents with **lower abdominal pain**, **cervical motion tenderness**, and purulent vaginal discharge, rather than rapid-onset systemic shock and generalized diffuse rash. - Although PID is an ascending infection often causing fever, it rarely leads to the swift and profound **hypotension** and multi-organ dysfunction characteristic of TSS. Streptococcal pharyngitis - This infection primarily presents with **sore throat**, fever, and sometimes exudates on the tonsils; it is locally confined and generally does not cause sudden, severe **hypotension** or systemic collapse. - While *Streptococcus pyogenes* can also cause a toxic shock syndrome, simple pharyngitis lacks the multi-system involvement, hypotensive crisis, and definitive association with **tampon usage** seen in this presentation. [1]

Question 706: A patient presents with fever after returning from a forest trip. On examination, a black eschar is noted on the abdomen. Which of the following is the most likely diagnosis and its drug of choice?

A. Ceftriaxone
B. Penicillin
C. Artesunate
D. Doxycycline (Correct Answer)

Explanation: ***Doxycycline (Scrub Typhus)*** - The clinical presentation of fever following a forest trip, along with a characteristic **black eschar** (tache noire), is highly suggestive of **scrub typhus**, a rickettsial infection caused by *Orientia tsutsugamushi*. - **Doxycycline** is the drug of choice for rickettsial diseases, including scrub typhus, as it effectively inhibits protein synthesis in these obligate intracellular bacteria. - The diagnosis is scrub typhus, and doxycycline is the first-line treatment with rapid clinical response typically within 24-48 hours. *Penicillin* - Penicillin targets bacterial **cell wall synthesis** and is primarily effective against gram-positive organisms like *Streptococcus* and *Staphylococcus*. - It is ineffective against intracellular pathogens like *Orientia tsutsugamushi*, which lack a typical peptidoglycan cell wall targeted by penicillins. *Ceftriaxone* - Ceftriaxone is a third-generation cephalosporin used for a wide range of bacterial infections, such as meningitis and community-acquired pneumonia, but it is not the standard treatment for rickettsial diseases. - Clinical trials have shown that tetracyclines like doxycycline result in faster defervescence and better outcomes for scrub typhus compared to cephalosporins. *Artesunate* - Artesunate is a potent **antimalarial** drug used for treating severe malaria caused by *Plasmodium* species. - While malaria can cause fever after travel, it does not produce a necrotic eschar, which is a key diagnostic feature distinguishing scrub typhus from malaria.

Question 707: A patient presents with blackish discoloration of the nasal cavity and posterior buccal mucosa. He has a history of high-dose steroid use. What is the most appropriate drug for treatment?

A. Amphotericin B (Correct Answer)
B. Fluconazole
C. Griseofulvin
D. Itraconazole

Explanation: ***Amphotericin B*** - The patient's signs (**blackish discoloration** of the nasal and buccal mucosa) coupled with profound immunosuppression (high-dose steroids) strongly suggest **Rhinocerebral mucormycosis**, an aggressive angioinvasive fungal infection caused by **Mucorales** [2]. - **Amphotericin B** (liposomal formulation preferred) is the drug of choice for empirical and definitive treatment of life-threatening mucormycosis due to its potent fungicidal activity against **Zygomycetes** [2]. - Early surgical debridement combined with Amphotericin B therapy is essential for optimal outcomes [2]. *Fluconazole* - **Fluconazole** has no reliable activity against **Mucorales** (causative agents of mucormycosis) [3]. - It is primarily used for *Candida* and *Cryptococcus* infections, completely lacking the spectrum needed for this severe angioinvasive process [1][3]. *Itraconazole* - **Itraconazole** is typically ineffective against **Mucorales** and is generally reserved for endemic mycoses (*Histoplasma, Blastomyces*) or step-down therapy for *Aspergillus* [3]. - It does not achieve adequate fungicidal activity needed for aggressive invasive fungal sinusitis. *Griseofulvin* - **Griseofulvin** is indicated only for **dermatophytosis** (superficial tinea infections of skin, hair, and nails). - It has no role or efficacy in treating severe, systemic, or angioinvasive fungal infections like mucormycosis.

Question 708: CSF shows abundant PMNs with low sugar and elevated proteins. Diagnosis is?

A. Viral encephalitis
B. Tubercular Meningitis
C. Acute bacterial meningitis (Correct Answer)
D. Viral meningitis

Explanation: ***Acute bacterial meningitis*** - The findings of abundant **Polymorphonuclear leukocytes (PMNs)**, **low CSF glucose** (due to bacterial consumption), and **elevated protein** are the classic triad for an acute bacterial infection of the meninges [1]. - A high PMN count indicates an acute inflammatory response, and the profound hypoglycemia and marked protein elevation distinguish it from most viral etiologies [1]. *Tubercular Meningitis* - While also associated with **low CSF glucose** and **elevated protein**, the predominant cell type is typically **lymphocytic** (mononuclear cells), not PMNs [3]. - The CSF often appears xanthochromic, and organisms like *M. tuberculosis* generally cause a subacute or chronic presentation rather than the acute presentation suggested by abundant PMN presence [3]. *Viral encephalitis* - CSF analysis usually reveals a **lymphocytic pleocytosis** (a higher proportion of lymphocytes), not a PMN predominance. - Glucose levels are typically **normal**, and protein elevation is usually mild to moderate, not markedly elevated. *Viral meningitis* - Similar to viral encephalitis, viral meningitis primarily causes a **lymphocytic pleocytosis** with a transient PMN phase early on, which quickly shifts to lymphocytes [2]. - The defining feature differentiating it from bacterial or tubercular meningitis is the **normal CSF glucose** level and milder protein elevation [2].

Question 709: What is the management of undulant fever?

A. Doxycycline
B. Doxycycline plus ceftriaxone
C. Doxycycline plus rifampicin (Correct Answer)
D. Doxycycline with azithromycin

Explanation: ***Doxycycline plus rifampicin***- This is the **standard and preferred oral combination regimen** for treating **Brucellosis** (undulant fever), typically administered for 6 weeks [1].- The combination is crucial because it uses antibiotics that penetrate macrophages and have a **synergistic effect**, significantly reducing the risk of relapse compared to monotherapy.*Doxycycline*- **Doxycycline** is the cornerstone of treatment due to its excellent **intracellular penetration**, but **monotherapy** is associated with high rates of **relapse**.- It must be combined with a second agent (like **rifampicin** or **streptomycin**) to achieve adequate cure rates and prevent recurrence.*Doxycycline with azithromycin*- While macrolides like **azithromycin** show *in vitro* activity against *Brucella*, clinical data supporting this combination as a first-line treatment are generally lacking.- This combination is **less effective** and not recommended by major professional guidelines compared to regimens using **rifampicin** or aminoglycosides.*Doxycycline plus ceftriaxone*- **Ceftriaxone** (a third-generation cephalosporin) is used primarily for complicated brucellosis, especially **neurobrucellosis** (often added to the standard regimen).- It is **not recommended** as part of the standard initial **oral** regimen for uncomplicated brucellosis due to inferior efficacy compared to rifampicin.

Question 710: A patient presents with fever and altered sensorium. Peripheral smear shows multiple ring stages. Best treatment is?

A. Artesunate (Correct Answer)
B. Chloroquine
C. Primaquine
D. Quinine

Explanation: Artesunate - The clinical presentation of fever and altered sensorium, along with a peripheral smear showing multiple ring stages (characteristic of P. falciparum), indicates severe malaria [1]. Intravenous artesunate is the recommended first-line treatment [1]. - Artesunate is a potent and rapidly acting artemisinin derivative that quickly reduces the parasite burden, leading to lower mortality rates compared to quinine in severe malaria cases [1]. Primaquine - Primaquine is primarily used to eradicate the dormant liver stages (hypnozoites) of P. vivax and P. ovale to prevent relapse, not for treating acute, severe falciparum malaria. - It is ineffective against the asexual erythrocytic stages of P. falciparum and can cause severe hemolysis in patients with G6PD deficiency. Quinine - Quinine is a second-line agent for severe malaria and is only used if artesunate is unavailable, due to its inferior efficacy and greater toxicity [1]. - Its use is associated with adverse effects known as cinchonism (tinnitus, headache, nausea) and can cause severe hypoglycemia and cardiac arrhythmias [1]. Chloroquine - Widespread resistance of P. falciparum to chloroquine makes it an ineffective choice for treating this infection in most malaria-endemic regions. - Chloroquine is typically reserved for the treatment of uncomplicated malaria caused by chloroquine-sensitive species like P. malariae, _P. ovale, or P. vivax (in areas without resistance).

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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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