Infectious Diseases — MCQs

A 62-year-old man presents with new symptoms of fevers, chills, and malaise. His past medical history is significant for a prosthetic aortic valve replacement 5 years ago due to aortic stenosis from a bicuspid valve. On physical examination, the blood pressure is 130/85 mm Hg, heart rate is 88/min, and temperature is 38.5°C. He has a 2/6 systolic ejection murmur heard best at the aortic region and a mechanical second heart sound, but no other abnormalities on examination. Blood cultures are most likely to grow which of the following organisms?

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 291: Prodromal symptom complex of tetanus consists of which of the following?

A. Restlessness
B. Headache
C. Masseter muscle spasm
D. All the above (Correct Answer)

Explanation: Tetanus is caused by the neurotoxin **tetanospasmin**, produced by *Clostridium tetani*. The clinical presentation typically follows an incubation period (usually 3–21 days) and begins with a non-specific prodromal phase before the onset of classic generalized muscle spasms [1]. 1. **Restlessness and Irritability:** These are among the earliest signs of autonomic nervous system involvement and neuromuscular irritability. Patients often feel an unexplained sense of unease or anxiety. 2. **Headache:** This is a common early constitutional symptom. Along with low-grade fever and malaise, it reflects the initial systemic response to the toxin. 3. **Masseter Muscle Spasm (Trismus):** While trismus is the hallmark of "Lockjaw," it often begins as a subtle stiffness or mild spasm of the masseter muscles during the prodromal phase before progressing to full-blown rigidity. Since all three symptoms—restlessness, headache, and early masseter involvement—characterize the transition from the incubation period to the clinical disease, **Option D (All the above)** is the correct choice. **High-Yield Clinical Pearls for NEET-PG:** * **Descending Paralysis:** Tetanus typically follows a descending pattern: Trismus (Lockjaw) → Risus Sardonicus (facial grin) → Opisthotonus (archback) → Respiratory failure. * **Diagnosis:** It is a **clinical diagnosis**. Laboratory tests (like wound cultures) are often negative and not required for treatment. * **Spatula Test:** A high-yield bedside test where touching the oropharynx triggers a reflex bite (positive) instead of a gag reflex (negative). * **Management:** The priority is neutralizing unbound toxin with **Human Tetanus Immune Globulin (HTIG)** and controlling spasms with benzodiazepines.

Question 292: A 26-year-old patient presents with suspected pneumococcal meningitis. CSF culture is sent for antibiotic sensitivity. Which empirical antibiotic should be given until culture sensitivity results are available?

A. Penicillin G
B. Ceftriaxone + metronidazole
C. Doxycycline
D. Cefotaxime + vancomycin (Correct Answer)

Explanation: **Explanation:** The management of bacterial meningitis is a medical emergency requiring immediate empirical antibiotic therapy. The choice of drugs is guided by the most likely pathogens and current resistance patterns. [2] **1. Why Option D is Correct:** * **Streptococcus pneumoniae** is the most common cause of community-acquired bacterial meningitis in adults. [1] * Due to the rising prevalence of **penicillin-resistant** and **cephalosporin-resistant** pneumococci, monotherapy with a third-generation cephalosporin (Cefotaxime or Ceftriaxone) is no longer sufficient. * **Vancomycin** is added empirically to ensure coverage against these highly resistant strains. Once culture sensitivity results are available, the regimen can be narrowed. **2. Why Other Options are Incorrect:** * **Option A (Penicillin G):** While historically the drug of choice, it is no longer used empirically due to widespread high-level penicillin resistance in *S. pneumoniae*. * **Option B (Ceftriaxone + Metronidazole):** Ceftriaxone is appropriate, but Metronidazole is used for anaerobic coverage (e.g., brain abscesses) and has no role in the standard empirical treatment of community-acquired pneumococcal meningitis. [3] * **Option C (Doxycycline):** This is a bacteriostatic drug with poor CNS penetration and is not indicated for the treatment of acute bacterial meningitis. **Clinical Pearls for NEET-PG:** * **Steroids:** Dexamethasone should be administered **before or with** the first dose of antibiotics to reduce neurological complications (hearing loss, edema). [1] * **Age-specific coverage:** In patients >50 years or those who are immunocompromised, **Ampicillin** must be added to the regimen to cover *Listeria monocytogenes*. * **CSF Findings:** Classic bacterial meningitis shows high opening pressure, high protein (>45 mg/dL), low glucose (<40 mg/dL), and neutrophilic pleocytosis. [1]

Question 293: Hepatitis C is associated with all of the following except:

A. Polyarteritis nodosa (PAN)
B. Dermatomyositis-like syndrome (Correct Answer)
C. Lichen planus
D. All of the above

Explanation: **Explanation:** Hepatitis C Virus (HCV) is a systemic infection known for its numerous extrahepatic manifestations, primarily mediated by immune complex deposition and chronic immune activation. **Why Dermatomyositis-like syndrome is the correct answer:** Dermatomyositis-like syndrome is classically associated with **Hepatitis B Virus (HBV)** and certain malignancies, but it is not a recognized association of Hepatitis C. While HCV can cause various skin and muscle symptoms, it does not typically present with the specific inflammatory myopathy and heliotrope rash characteristic of dermatomyositis. **Analysis of other options:** * **Polyarteritis nodosa (PAN):** While PAN is most famously associated with Hepatitis B (up to 30% of cases), it is also documented in patients with **Hepatitis C** [1]. However, HCV is more strongly linked to **Mixed Cryoglobulinemia (Type II)**, which presents as a small-vessel vasculitis. * **Lichen planus:** There is a statistically significant correlation between HCV infection and Lichen planus (especially the oral form). It is a high-yield association frequently tested in postgraduate exams. **High-Yield Clinical Pearls for NEET-PG:** * **Most common HCV association:** Mixed Cryoglobulinemia (presents with Meltzer’s triad: purpura, arthralgia, and weakness). * **Renal association:** Membranoproliferative glomerulonephritis (MPGN). * **Dermatological associations:** Porphyria cutanea tarda (PCT) and Lichen planus. * **Endocrine association:** Type 2 Diabetes Mellitus and Autoimmune Thyroiditis [2]. * **B-cell Lymphoma:** Chronic HCV stimulation can lead to Non-Hodgkin Lymphoma.

Question 294: A 10-year-old school girl has recurrent episodes of boils on the scalp. The boils subside with antibiotic therapy but recur after some time. What is the most likely cause of these recurrences?

A. Primary immunodeficiency syndrome
B. Juvenile diabetes mellitus
C. Pediculosis capitis (Correct Answer)
D. HPV infection

Explanation: **Explanation:** The clinical presentation of recurrent boils (furunculosis) on the scalp of a school-going girl, which respond to antibiotics but recur shortly after, is a classic sign of an underlying **predisposing factor** rather than a primary infectious failure [1]. **Why Pediculosis Capitis is the correct answer:** Pediculosis capitis (head lice) is the most common cause of recurrent scalp pyoderma in school-aged children. The lice cause intense pruritus; subsequent scratching leads to **micro-abrasions and skin breaches**. These breaches serve as a portal of entry for commensal bacteria like *Staphylococcus aureus*, leading to secondary bacterial infections (boils/impetigo) [1]. While antibiotics clear the current infection, they do not eliminate the lice. The persistent itching and scratching cycle leads to inevitable recurrence. **Analysis of Incorrect Options:** * **Primary Immunodeficiency:** While these can cause recurrent infections, they typically present with systemic involvements (pneumonia, abscesses in deep organs, or failure to thrive) rather than localized scalp boils alone. * **Juvenile Diabetes Mellitus:** Poor glycemic control predisposes to skin infections, but it is a less common cause in this specific age group compared to the high prevalence of head lice in schools. It would usually present with systemic symptoms like polyuria or weight loss. * **HPV Infection:** Human Papillomavirus causes warts (verrucae), not acute inflammatory boils or furuncles. **NEET-PG Clinical Pearls:** * In any case of **recurrent pyoderma** in children, always look for an underlying itchy dermatosis (Lice, Scabies, or Atopic Dermatitis) [1]. * **Occipital lymphadenopathy** is a common physical finding associated with secondary infection in pediculosis capitis. * The drug of choice for Pediculosis capitis is **Topical Permethrin (1%)**; alternatively, Ivermectin can be used.

Question 295: All are true about post-meningococcal reactive disease, EXCEPT?

A. Develops after 4 weeks of meningococcal disease (Correct Answer)
B. Maculopapular or vasculitic rash and polyserositis
C. These features resolve spontaneously without sequelae
D. Antibiotic prophylaxis is not needed

Explanation: ### Explanation **Post-meningococcal Reactive Disease (PMRD)** is an immune-mediated phenomenon that occurs during the recovery phase of meningococcal meningitis. **1. Why Option A is the Correct Answer (The "Except"):** The timing in Option A is incorrect. PMRD typically develops **4 to 10 days** after the onset of the initial meningococcal illness, not 4 weeks. It is characterized by an immune-complex mediated (Type III hypersensitivity) reaction as the patient is recovering from the acute infection. **2. Analysis of Other Options:** * **Option B:** The clinical triad of PMRD includes **arthritis** (most common), **maculopapular or vasculitic rash**, and **polyserositis** (such as pleurisy or pericarditis). Fever often recurs during this phase. * **Option C:** The condition is self-limiting. These immune-mediated features **resolve spontaneously** within 1 to 2 weeks without causing permanent joint damage or long-term sequelae. * **Option D:** Since PMRD is an **immunological reaction** and not a relapse of the bacterial infection, additional or prolonged antibiotic prophylaxis is not indicated. Treatment is primarily supportive, using NSAIDs for pain and inflammation. **Clinical Pearls for NEET-PG:** * **Pathogenesis:** It is caused by the deposition of circulating immune complexes (meningococcal antigen + antibody) in synovial tissues and blood vessels. * **Synovial Fluid:** If joints are aspirated, the fluid is usually sterile (culture negative) with a high polymorphonuclear leukocyte count. * **Differential Diagnosis:** It must be distinguished from a treatment failure or secondary infection; however, the patient with PMRD usually appears clinically stable despite the new-onset fever and joint pain.

Question 296: Relapse in malaria is seen in which Plasmodium species?

A. P. malariae and P. ovale
B. P. vivax and P. malariae
C. P. falciparum and P. ovale
D. P. vivax, P. ovale, and P. malariae (Correct Answer)

Explanation: ### Explanation The correct answer is **D (P. vivax, P. ovale, and P. malariae)**. **Understanding the Concept: Relapse vs. Recrudescence** In malaria, a clinical recurrence of symptoms can occur via two distinct mechanisms: 1. **Relapse:** This is caused by the reactivation of **hypnozoites**—dormant stages of the parasite that remain in the liver (exo-erythrocytic cycle). While **P. vivax** and **P. ovale** are the classic species known for hypnozoite formation [1], recent clinical evidence and standard textbooks (including Harrison’s Principles of Internal Medicine) acknowledge that **P. malariae** can also cause long-term clinical recurrences. 2. **Recrudescence:** This occurs when a sub-clinical population of parasites persists in the **bloodstream** (erythrocytic cycle) due to inadequate treatment or drug resistance. This is the primary mechanism for recurrence in **P. falciparum** and **P. malariae** [1]. **Analysis of Options:** * **P. vivax and P. ovale:** These are the most common species associated with true relapse via hypnozoites [1]. * **P. malariae:** While it does not technically form hypnozoites, it is famous for "delayed manifestation" or "long-term persistence" in the blood for decades [1]. In the context of NEET-PG, it is often grouped with relapsing species because it causes clinical recurrence long after the initial infection. * **P. falciparum:** This species does **not** have a liver stage (hypnozoite) and does not cause relapse [1]. Any recurrence is strictly due to recrudescence. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice for Relapse:** **Primaquine** or **Tafenoquine** is mandatory to clear the liver stages (radical cure). * **G6PD Deficiency:** Always screen for G6PD deficiency before administering Primaquine to avoid acute hemolysis. * **P. malariae Fact:** It is associated with **Quartan malaria** (72-hour fever spikes) and **Nephrotic Syndrome** (specifically Quartan Malarial Nephropathy). * **P. falciparum Fact:** Associated with **Malignant Tertian malaria** and complications like Cerebral Malaria and Blackwater Fever.

Question 297: A 49-year-old gentleman undergoes a root canal procedure. A few days later, he develops fever, weight loss, and anorexia. He is diagnosed with mitral valve prolapse with mitral regurgitation. What is the most common organism implicated in the causation of this condition?

A. Streptococcus pneumoniae
B. Staphylococcus aureus
C. Viridans streptococci (Correct Answer)
D. Providencia stuartii

Explanation: ### Explanation This clinical scenario describes **Subacute Bacterial Endocarditis (SBE)**. The patient has a pre-existing structural heart defect (**Mitral Valve Prolapse with Mitral Regurgitation**) and recently underwent a dental procedure (**root canal**), which are classic triggers for this condition [1]. **Why Viridans streptococci is correct:** *Viridans group streptococci* (including *S. mitis, S. sanguinis, and S. mutans*) are normal flora of the oropharynx [1]. Dental manipulations cause transient bacteremia, allowing these low-virulence organisms to settle on damaged or abnormal heart valves (like MVP with MR) [1]. They produce **dextran**, which facilitates adherence to fibrin-platelet aggregates, leading to the formation of vegetations [1]. This typically follows a subacute course characterized by fever, weight loss, and anorexia [1]. **Why the other options are incorrect:** * **Staphylococcus aureus:** This is the most common cause of **Acute** Infective Endocarditis, often affecting healthy valves [1]. It is the leading cause in IV drug users and healthcare-associated infections [1]. * **Streptococcus pneumoniae:** While it can cause endocarditis (part of the Austrian Syndrome triad), it is an uncommon cause and usually presents acutely with high-grade fever and rapid valve destruction [1]. * **Providencia stuartii:** This is a Gram-negative rod typically associated with urinary tract infections (especially in catheterized patients) and burn wound infections, not endocarditis. **High-Yield Clinical Pearls for NEET-PG:** * **Most common cause of IE overall:** *Staphylococcus aureus* [1]. * **Most common cause of IE in Native Valves (Subacute):** *Viridans streptococci* [1]. * **Most common cause in Prosthetic Valves (<1 year):** *Staphylococcus epidermidis*. * **Culture-negative IE:** Most commonly due to *Coxiella burnetii* or HACEK organisms [2]. * **MVP with MR:** This is the most common predisposing underlying heart condition for IE in developed countries [3].

Question 298: Which of the following statements regarding diarrhea in HIV infection is incorrect?

A. Diarrhea due to Salmonella has a greater incidence of associated bacteremia and may require chronic suppressive antibiotic therapy.
B. The most common parasites associated with diarrhea in HIV infection are Giardia lamblia, Entamoeba histolytica, and Cryptosporidium.
C. Mycobacterium avium complex may cause diarrhea due to malabsorption, which responds well to treatment. (Correct Answer)
D. Cryptosporidium is diagnosed by acid-fast stain of intestinal biopsy or stool specimens, and there is no proven effective treatment.

Explanation: ### Explanation **Why Option C is Incorrect (The Correct Answer):** While *Mycobacterium avium* complex (MAC) is a common cause of diarrhea and malabsorption in advanced HIV (CD4 < 50 cells/µL), the statement is incorrect because MAC-associated diarrhea **does not respond well to treatment** [1]. Even with multidrug therapy (e.g., Clarithromycin and Ethambutol), clinical improvement is often slow, and complete eradication is difficult without significant immune reconstitution via Antiretroviral Therapy (ART). **Analysis of Other Options:** * **Option A:** HIV patients have a 20- to 100-fold increased risk of *Salmonella* bacteremia compared to immunocompetent hosts. Recurrence is common, often necessitating **chronic suppressive therapy** (secondary prophylaxis) with fluoroquinolones. * **Option B:** While *Cryptosporidium*, *Isospora*, and *Microsporidia* are classic HIV-associated pathogens [1], *Giardia lamblia* and *Entamoeba histolytica* remain the most common parasites causing diarrhea in sexually active MSM (Men who have Sex with Men) populations, regardless of HIV status. * **Option D:** *Cryptosporidium* is a leading cause of chronic, watery diarrhea in HIV. It is diagnosed using **Modified Acid-Fast staining** [1]. Currently, there is **no proven curative antimicrobial**; the mainstay of treatment is immune reconstitution through ART [1]. **Clinical Pearls for NEET-PG:** * **CD4 Thresholds:** Diarrhea in HIV is often stage-specific. *Cryptosporidium* and MAC typically occur when **CD4 < 100/µL** and **< 50/µL**, respectively. * **CMV Colitis:** The most common viral cause of diarrhea in HIV; characterized by bloody stools and "owl’s eye" inclusion bodies on biopsy. * **Acid-Fast Organisms in Stool:** Remember the trio: *Cryptosporidium*, *Cyclospora*, and *Cystoisospora* (Isospora) [1].

Question 299: Antibiotic-associated diarrhea is most commonly caused by which organism?

A. Clostridioides difficile (Correct Answer)
B. Vibrio cholerae
C. Salmonella species
D. Klebsiella pneumoniae

Explanation: **Explanation:** **1. Why Clostridioides difficile is correct:** *Clostridioides difficile* (formerly *Clostridium*) is the most common identifiable cause of antibiotic-associated diarrhea (AAD) [1]. The underlying mechanism involves the disruption of normal colonic flora by broad-spectrum antibiotics (most commonly Clindamycin, Fluoroquinolones, and Cephalosporins). This allows *C. difficile* to colonize the gut and release **Toxin A (Enterotoxin)** and **Toxin B (Cytotoxin)**, leading to mucosal inflammation and, in severe cases, the formation of yellow-white plaques known as **Pseudomembranous colitis** [1]. **2. Why the other options are incorrect:** * **Vibrio cholerae:** Causes "rice-water" stools through a toxin-mediated mechanism (adenylate cyclase activation) but is associated with contaminated water/food, not antibiotic use. * **Salmonella species:** Typically causes food poisoning or enteric fever. While it causes diarrhea, it is not a sequela of antibiotic-induced flora disruption. * **Klebsiella pneumoniae:** While *K. oxytoca* is specifically linked to antibiotic-associated hemorrhagic colitis, *K. pneumoniae* is primarily a respiratory and urinary pathogen and is not the "most common" cause of AAD. **3. NEET-PG High-Yield Pearls:** * **Drug of Choice:** Oral **Vancomycin** or **Fidaxomicin** are first-line treatments. Metronidazole is now reserved for non-severe cases if other options are unavailable. * **Diagnosis:** The gold standard for toxin identification is the **Cell Cytotoxicity Assay**, but the most common initial tests are **GDH (Glutamate Dehydrogenase) screening** and **NAAT/PCR** for toxin genes [1]. * **Risk Factors:** Advanced age, prolonged hospitalization, and use of **Proton Pump Inhibitors (PPIs)** [1]. * **Alcohol-based rubs** are ineffective against *C. difficile* spores; handwashing with soap and water is mandatory.

Question 300: A 62-year-old man presents with new symptoms of fevers, chills, and malaise. His past medical history is significant for a prosthetic aortic valve replacement 5 years ago due to aortic stenosis from a bicuspid valve. On physical examination, the blood pressure is 130/85 mm Hg, heart rate is 88/min, and temperature is 38.5°C. He has a 2/6 systolic ejection murmur heard best at the aortic region and a mechanical second heart sound, but no other abnormalities on examination. Blood cultures are most likely to grow which of the following organisms?

A. Fungi
B. Bartonella
C. Diphtheroids
D. Staphylococcus epidermidis (Correct Answer)

Explanation: The patient presents with symptoms of **Prosthetic Valve Endocarditis (PVE)**. The key to identifying the causative organism in PVE is the **timing** of symptom onset after surgery. 1. **Why D is correct:** PVE is classified into early (<1 year) and late (>1 year) onset [1]. While **Staphylococcus epidermidis** (Coagulase-negative Staphylococci) is the most common cause of *early* PVE due to perioperative contamination, it remains a significant pathogen in late PVE as well. However, in the context of NEET-PG questions, if a patient has a prosthetic valve and the clinical picture suggests endocarditis, **Staphylococci** (specifically *S. epidermidis*) are the most frequently implicated organisms across various stages of the disease due to their ability to form biofilms on prosthetic material [1]. 2. **Why other options are incorrect:** * **A & B (Fungi/Bartonella):** These are causes of "Culture-Negative Endocarditis." While they occur, they are far less common than bacterial causes. * **C (Diphtheroids):** *Corynebacterium* species are rare causes of PVE and are usually considered contaminants unless isolated from multiple blood cultures. **Clinical Pearls for NEET-PG:** * **Early PVE (<12 months):** Most common organism is *Staphylococcus epidermidis*. * **Late PVE (>12 months):** The microbiology starts to resemble Native Valve Endocarditis (NVE) [4], with *Streptococcus* species and *Staphylococcus aureus* becoming more prevalent. However, *S. epidermidis* remains a high-yield answer for any prosthetic material infection. * **Duke’s Criteria:** Remember that a new valvular regurgitation or positive blood cultures are "Major Criteria" for diagnosis [2]. * **Treatment:** PVE caused by *S. epidermidis* usually requires a combination of Vancomycin + Rifampin + Gentamicin [3].

Practice by Chapter

Principles of Antimicrobial Therapy

Practice Questions

Fever of Unknown Origin

Practice Questions

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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