Infectious Diseases — MCQs

A 59-year-old man undergoes coronary bypass surgery and receives vancomycin prophylactically for 24 hours. On the ninth postoperative day, he develops a fever of 39.8°C (103°F) with a heart rate of 115 beats/min and a blood pressure of 105/65 mm Hg. The surgical site is healing well with no redness or discharge. His white blood cell count is 14,000/mm³ and urinalysis reveals many white blood cells per high-power field. Blood and urine cultures grow a non-lactose-fermenting oxidase-positive gram-negative rod. Which of the following antibiotics is most appropriate to treat this infection?

Q236Medium

Inflammation of nerve is seen in which of the following conditions?

Q237Medium

A farmer who handles goats and sheep is presenting with fever, muscle and joint pain, and rash. What is the most likely diagnosis?

Q238Easy

Which of the following statements is true about measles?

Q239Medium

What is the best treatment for a diabetic patient with the condition described below?

Q240Easy

What is the drug of choice in Bacteroides infections?

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 231: What is the causative agent responsible for the chronic carrier state in liver disease?

A. Hepatitis B virus (HBV) (Correct Answer)
B. Hepatitis A virus (HAV)
C. Hepatitis E virus (HEV)
D. Hepatitis C virus (HCV)

Explanation: **Explanation:** The chronic carrier state is defined as the persistence of the Hepatitis B surface antigen (**HBsAg**) in the blood for more than **6 months** [1]. Among the options provided, **Hepatitis B Virus (HBV)** is the classic causative agent associated with this state. The risk of becoming a chronic carrier is inversely proportional to the age at infection: approximately 90% of infected neonates become carriers, compared to only 5–10% of immunocompetent adults [1]. **Analysis of Options:** * **Hepatitis A (HAV) & Hepatitis E (HEV):** These are transmitted via the fecal-oral route and cause **acute** hepatitis only [2]. They do not progress to chronic infection or a carrier state (Exception: HEV can cause chronic infection in severely immunocompromised individuals/transplant recipients, but it is not the standard "carrier state" answer). * **Hepatitis C (HCV):** While HCV has a very high rate of **chronicity** (75–85% of cases), the term "chronic carrier state" (asymptomatic persistence with low viral replication) is traditionally and most frequently associated with HBV in medical literature and examinations. **NEET-PG High-Yield Pearls:** * **HBsAg:** First serological marker to appear; indicates active infection (acute or chronic) [1]. * **HBeAg:** Marker of high infectivity and active viral replication. * **Anti-HBs:** Indicates immunity (via recovery or vaccination) [1]. * **Window Period:** The interval when HBsAg disappears but Anti-HBs has not yet appeared; **Anti-HBc IgM** is the only diagnostic marker during this phase [1]. * **Ground-glass hepatocytes:** The characteristic histopathological finding in chronic HBV carriers.

Question 232: A nurse has been found to be seropositive for both HbsAg and HBeAg. She is suffering from which of the following conditions?

A. Concurrent Hepatitis B and Hepatitis E infection
B. Acute Hepatitis B infection (Correct Answer)
C. Chronic Hepatitis B infection
D. Past Hepatitis B infection

Explanation: ### Explanation The presence of **HBsAg** (Hepatitis B surface Antigen) indicates that the patient is currently infected with the Hepatitis B virus [1]. The presence of **HBeAg** (Hepatitis B envelope Antigen) is a marker of active viral replication and high infectivity. **Why Acute Hepatitis B is the correct answer:** In the clinical context of a healthcare worker (like a nurse) presenting with these markers, it typically represents an **Acute Hepatitis B infection**. During the early phase of acute infection, HBsAg appears first, followed closely by HBeAg [1]. While HBeAg can also be present in the "Immune Tolerant" or "Reactive" phases of chronic infection, in standard NEET-PG questions, the combination of HBsAg and HBeAg without further qualifiers (like duration >6 months) is the classic laboratory profile for a highly infectious acute case. **Analysis of Incorrect Options:** * **Option A:** HBeAg stands for "envelope" antigen of HBV, not Hepatitis E. Hepatitis E is a separate RNA virus diagnosed via Anti-HEV IgM. * **Option C:** Chronic infection is defined by the persistence of HBsAg for **more than 6 months** [1]. Without a longitudinal history, acute infection is the primary clinical assumption. * **Option D:** In a past/resolved infection, HBsAg is cleared and **Anti-HBs antibodies** are present [1]. HBeAg would also be absent. --- ### High-Yield Clinical Pearls for NEET-PG * **HBsAg:** First marker to appear; indicates current infection (acute or chronic) [1]. * **HBeAg:** Indicates **high viral load**, active replication, and maximum infectivity. * **Anti-HBc IgM:** The **best marker for Acute HBV** (especially during the "Window Period" when HBsAg and Anti-HBs are both negative) [1]. * **Anti-HBc IgG:** Indicates "Remote" infection; it persists for life. * **Anti-HBs:** Indicates **immunity** (either from recovery or vaccination) [1]. If it is the *only* positive marker, it indicates vaccination.

Question 233: A 19-year-old male tests positive for hepatitis C infection. He was arrested twice for stealing and belongs to a gang of friends. Which of the following is the most likely method of transmission?

A. Fecal-oral
B. Fomite
C. Sexual transmission
D. Intravenous drug use (Correct Answer)

Explanation: **Explanation:** The correct answer is **D. Intravenous drug use (IVDU).** Hepatitis C Virus (HCV) is primarily a **blood-borne pathogen**. [2] In developed and developing countries alike, the most common risk factor for HCV transmission is the sharing of needles and paraphernalia among intravenous drug users [3]. The clinical vignette provides behavioral clues—history of arrests for theft and gang affiliation—which are high-yield "social markers" in medical exams pointing toward a lifestyle associated with substance abuse and IVDU. **Analysis of Incorrect Options:** * **A. Fecal-oral:** This is the primary route for Hepatitis A and E ("The vowels hit the bowels"). HCV is not transmitted via the fecal-oral route. * **B. Fomite:** HCV is not typically spread through casual contact or inanimate objects (fomites) unless they are contaminated with fresh blood (e.g., shared razors or toothbrushes), but this is significantly less common than IVDU. * **C. Sexual transmission:** While possible, the efficiency of sexual transmission for HCV is remarkably low (unlike HBV or HIV). It is generally only a significant risk factor in individuals with multiple partners or co-infection with HIV. **NEET-PG High-Yield Pearls:** * **Most common cause of post-transfusion hepatitis:** Historically HCV, though now rare due to rigorous screening. * **Chronicity:** HCV has the highest rate of progression to chronic infection (~75–85%) among the hepatitis viruses. * **Screening:** Anti-HCV antibody is the initial screening test; HCV RNA (PCR) is the gold standard for confirming active infection. [1] * **Extrahepatic manifestations:** Essential mixed cryoglobulinemia, Membranoproliferative glomerulonephritis (MPGN), and Porphyria cutanea tarda (PCT).

Question 234: Treatment with what antibiotic is most likely to have resulted in this patient's skin changes?

A. Rifampin
B. Chloramphenicol
C. Nitrofurantoin
D. Minocycline (Correct Answer)

Explanation: ***Minocycline*** - **Minocycline** is well-known for causing distinctive **blue-grey to blue-black skin hyperpigmentation**, particularly in sun-exposed areas and mucous membranes. - This **irreversible pigmentation** occurs due to deposition of **minocycline-melanin complexes** in tissues, making it a classic adverse effect of long-term tetracycline therapy. *Rifampin* - **Rifampin** typically causes **orange-red discoloration** of body fluids (urine, tears, saliva) but not the blue-grey skin changes described. - Known adverse effects include **hepatotoxicity** and **flu-like syndrome**, not characteristic skin pigmentation. *Chloramphenicol* - **Chloramphenicol** is associated with serious **bone marrow suppression** (aplastic anemia) and **grey baby syndrome** in neonates. - Does not cause the distinctive **blue-grey skin hyperpigmentation** characteristic of minocycline therapy. *Nitrofurantoin* - **Nitrofurantoin** commonly causes **pulmonary toxicity** (acute pneumonitis, chronic fibrosis) and **peripheral neuropathy**. - Skin pigmentation changes are not a recognized adverse effect of **nitrofurantoin** therapy.

Question 235: A 59-year-old man undergoes coronary bypass surgery and receives vancomycin prophylactically for 24 hours. On the ninth postoperative day, he develops a fever of 39.8°C (103°F) with a heart rate of 115 beats/min and a blood pressure of 105/65 mm Hg. The surgical site is healing well with no redness or discharge. His white blood cell count is 14,000/mm³ and urinalysis reveals many white blood cells per high-power field. Blood and urine cultures grow a non-lactose-fermenting oxidase-positive gram-negative rod. Which of the following antibiotics is most appropriate to treat this infection?

A. Moxifloxacin
B. Ceftriaxone
C. Imipenem (Correct Answer)
D. Trimethoprim-sulfamethoxazole

Explanation: ### Explanation **1. Why Imipenem is Correct:** The clinical presentation describes a healthcare-associated infection (likely a UTI/urosepsis) following surgery. The key to the diagnosis lies in the microbiology: a **non-lactose-fermenting, oxidase-positive, Gram-negative rod**. This description is classic for ***Pseudomonas aeruginosa***. Among the options provided, **Imipenem** (a carbapenem) is a potent anti-pseudomonal agent [1]. It is highly effective against multidrug-resistant Gram-negative bacteria often encountered in hospital settings. **2. Why the Other Options are Incorrect:** * **Moxifloxacin (Option A):** While it is a respiratory fluoroquinolone, it lacks reliable activity against *Pseudomonas*. Ciprofloxacin and Levofloxacin are the only fluoroquinolones with anti-pseudomonal activity. * **Ceftriaxone (Option B):** This is a third-generation cephalosporin. While it covers many Gram-negative rods, it has **no activity** against *Pseudomonas*. * **Trimethoprim-sulfamethoxazole (Option D):** This is typically used for uncomplicated UTIs or specific organisms like *Stenotrophomonas*, but it is not effective against *Pseudomonas*. **3. Clinical Pearls for NEET-PG:** * **Pseudomonas Identification:** Gram-negative rod, Oxidase positive, Non-lactose fermenter (NLF), produces pigments (Pyocyanin/Pyoverdin), and has a characteristic "fruity/grape-like" odor. * **Anti-pseudomonal "Must-Knows":** * **Penicillins:** Piperacillin-Tazobactam (Pip-Tazo). * **Cephalosporins:** Ceftazidime (3rd gen), Cefepime (4th gen). * **Carbapenems:** Imipenem, Meropenem (**Note:** *Ertapenem* does NOT cover Pseudomonas). * **Fluoroquinolones:** Ciprofloxacin, Levofloxacin. * **Monobactams:** Aztreonam. * **Aminoglycosides:** Amikacin, Gentamicin, Tobramycin.

Question 236: Inflammation of nerve is seen in which of the following conditions?

A. Leprosy
B. Diabetes Mellitus (Correct Answer)
C. Guillain-Barré Syndrome
D. Diphtheria

Explanation: The question asks for the condition characterized by **inflammation** of the nerve (Neuritis), rather than just degeneration or demyelination. ### **Explanation of the Correct Answer** **B. Diabetes Mellitus:** While diabetic neuropathy is primarily metabolic and vascular (microangiopathy of vasa nervorum), certain subtypes involve significant inflammatory components [1]. Specifically, **Diabetic Amyotrophy** (Proximal Diabetic Neuropathy) is characterized by **ischaemic nerve infarction secondary to an immune-mediated microvasculitis**. Biopsies in these cases show perivascular inflammatory infiltrates, making "inflammation of the nerve" a histopathological feature of this specific diabetic complication. ### **Why the Other Options are Incorrect** * **A. Leprosy:** Although leprosy is the most common cause of nerve *enlargement* and damage worldwide, the primary pathology is a chronic granulomatous infection. While there is an immune response, the term "neuritis" in the context of this specific question's framing (often sourced from standard textbooks like Harrison’s) distinguishes the metabolic/vasculitic inflammation of DM from the granulomatous destruction in Leprosy. * **C. Guillain-Barré Syndrome (GBS):** GBS is primarily an **acute inflammatory demyelinating polyradiculoneuropathy (AIDP)** [2]. The focus is on the myelin sheath and nerve roots rather than the nerve parenchyma itself. * **D. Diphtheria:** Nerve damage in Diphtheria is caused by a **circulating exotoxin** that leads to paranodal demyelination. It is a toxic neuropathy, not a primary inflammatory neuritis. ### **NEET-PG Clinical Pearls** * **Most common cause of peripheral neuropathy:** Diabetes Mellitus [1]. * **Most common cause of nerve thickening:** Leprosy (others include Amyloidosis, CMT, and Refsum disease). * **Diabetic Amyotrophy (Bruns-Garland Syndrome):** Presents as acute, asymmetrical, painful weakness of the proximal thigh muscles (L2-L4) in elderly Type 2 Diabetics. * **Key Distinction:** In exams, if "inflammation of nerve" is linked to DM, think of the **vasculitic** basis of proximal neuropathy.

Question 237: A farmer who handles goats and sheep is presenting with fever, muscle and joint pain, and rash. What is the most likely diagnosis?

A. Melioidosis
B. Brucellosis (Correct Answer)
C. Malaria
D. Glanders

Explanation: **Explanation:** **Brucellosis** is the most likely diagnosis given the patient's occupation and clinical presentation. It is a classic zoonotic infection transmitted to humans through direct contact with infected animals (goats, sheep, cattle, pigs) or by consuming unpasteurized dairy products. 1. **Why Brucellosis is correct:** The triad of **occupational exposure** (farming goats/sheep), **constitutional symptoms** (fever, arthralgia, myalgia), and a **rash** (though less common than fever, it can occur) points strongly toward *Brucella melitensis* (common in goats/sheep) [1]. The fever is often "undulant" (rising and falling like waves). 2. **Why other options are incorrect:** * **Melioidosis:** Caused by *Burkholderia pseudomallei*, it is typically associated with exposure to **soil and surface water** (e.g., rice farmers), not specifically goats or sheep. It often presents with pulmonary involvement or abscesses. * **Malaria:** While it causes fever and body aches, it is transmitted by the *Anopheles* mosquito. It lacks a specific association with livestock handling. * **Glanders:** Caused by *Burkholderia mallei*, this is primarily a disease of **horses, donkeys, and mules**. While it is zoonotic, the specific mention of goats and sheep makes Brucellosis the superior choice. **High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard Diagnosis:** Bone marrow culture (more sensitive than blood culture) [1]. * **Standard Serology:** Standard Agglutination Test (SAT); titers >1:160 are significant [1]. * **Treatment:** WHO recommends **Rifampicin + Doxycycline** for 6 weeks [1]. For complications like spondylitis or endocarditis, Streptomycin is often added. * **Key Association:** Look for "Undulant fever" and "Malta fever" in clinical vignettes.

Question 238: Which of the following statements is true about measles?

A. It is an RNA virus.
B. Causes Koplik's spots on the buccal mucosa.
C. Acute catarrhal conjunctivitis is a known feature.
D. All the above. (Correct Answer)

Explanation: Measles (Rubeola) is a highly contagious viral infection caused by the **Measles virus**, which belongs to the genus *Morbillivirus* within the *Paramyxoviridae* family. 1. **Option A (RNA Virus):** The measles virus is a single-stranded, negative-sense, enveloped **RNA virus**. Understanding its genomic structure is high-yield, as it lacks the genetic stability of DNA viruses but remains antigenically stable. 2. **Option B (Koplik’s Spots):** These are the **pathognomonic** hallmark of measles [1]. They appear during the prodromal stage as small, bluish-white grains of sand on an erythematous base, typically located on the buccal mucosa opposite the lower second molars. They appear 48 hours before the characteristic maculopapular rash [1]. 3. **Option C (Acute Catarrhal Conjunctivitis):** Measles is clinically characterized by the "3 Cs": **Cough, Coryza, and Conjunctivitis**. The conjunctivitis is often associated with photophobia and excessive lacrimation, occurring during the catarrhal (prodromal) stage. Since all three statements accurately describe the virology and clinical presentation of the disease, **Option D** is the correct answer. **High-Yield Clinical Pearls for NEET-PG:** * **Rash Progression:** The maculopapular rash starts behind the ears (retro-auricular) and spreads cephalocaudally (head to toe) [1]. It disappears in the same order, leaving behind brownish discoloration/desquamation. * **Vitamin A:** Supplementation is recommended for all children with acute measles to reduce morbidity and mortality (especially blindness and pneumonia). * **Complications:** The most common complication is **Otitis Media**; the most common cause of death is **Pneumonia** [1]. * **SSPE:** Subacute Sclerosing Panencephalitis is a rare, delayed neurological complication occurring years after the initial infection [1].

Question 239: What is the best treatment for a diabetic patient with the condition described below?

A. Ceftriaxone
B. Vancomycin
C. Amphotericin (Correct Answer)
D. Ketoconazole

Explanation: ***Correct Answer: Amphotericin B*** The image shows **rhinocerebral mucormycosis** — a life-threatening fungal infection caused by *Mucor*, *Rhizopus*, or *Rhizomucor* species, seen characteristically in **poorly controlled diabetic patients** (especially those in diabetic ketoacidosis). **Key clinical features:** - **Black necrotic eschar** on nasal mucosa, hard palate, or periorbital region - Rapid spread to sinuses, orbit, and brain - Strongly associated with **diabetes mellitus** (high glucose + acidosis impairs phagocyte function) **Why Amphotericin B is correct:** - **Drug of choice** for mucormycosis - Liposomal Amphotericin B (L-AmB) is preferred for lower nephrotoxicity - Mucorales are **intrinsically resistant** to azole antifungals (including ketoconazole, fluconazole, voriconazole) *Incorrect: Ketoconazole* - An azole antifungal — **not effective** against Mucorales due to intrinsic azole resistance - Would be appropriate for dermatophytosis or candidiasis, not mucormycosis *Incorrect: Ceftriaxone* - A 3rd-generation cephalosporin (antibiotic) — **no antifungal activity** - Irrelevant for this fungal infection *Incorrect: Vancomycin* - A glycopeptide antibiotic active against Gram-positive bacteria (MRSA, etc.) — **no antifungal activity** - Completely ineffective against Mucorales **Key mnemonic:** "Mucor = Must use Amphotericin — azoles fail!"

Question 240: What is the drug of choice in Bacteroides infections?

A. Gentamicin
B. Metronidazole (Correct Answer)
C. Tigecycline
D. Penicillin

Explanation: **Explanation:** *Bacteroides fragilis* is the most clinically significant anaerobic, Gram-negative bacillus, commonly implicated in intra-abdominal infections, pelvic inflammatory disease, and abscesses. **1. Why Metronidazole is the Correct Answer:** Metronidazole is considered the **drug of choice** for most anaerobic infections, particularly those caused by the *Bacteroides* group [1]. Its mechanism involves the reduction of its nitro group by anaerobic electron transport proteins (like ferredoxin), creating toxic free radicals that disrupt bacterial DNA. It possesses excellent tissue penetration and remains highly effective despite increasing resistance to other antibiotics. **2. Why the Other Options are Incorrect:** * **Gentamicin:** This is an aminoglycoside. Aminoglycosides require oxygen for uptake into the bacterial cell; therefore, they have **zero activity** against obligate anaerobes like *Bacteroides* [1]. * **Tigecycline:** While Tigecycline has a broad spectrum that includes anaerobes, it is generally reserved for multidrug-resistant (MDR) infections or complicated skin/intra-abdominal infections, as there is an associated excess mortality [1]. It is not the first-line "drug of choice" for isolated *Bacteroides* infections. * **Penicillin:** Most *Bacteroides* species (especially *B. fragilis*) produce **beta-lactamases**, making them inherently resistant to Penicillin G and early-generation cephalosporins [1]. **Clinical Pearls for NEET-PG:** * **"Below the Diaphragm":** Metronidazole is the preferred anaerobic coverage for infections below the diaphragm [1]. * **"Above the Diaphragm":** For anaerobic infections above the diaphragm (e.g., aspiration pneumonia, lung abscess), **Clindamycin** is often preferred, though *Bacteroides* resistance to Clindamycin is rising. * **Alternative Agents:** Other effective drugs against *Bacteroides* include Carbapenems (Imipenem/Meropenem) and Beta-lactam/Beta-lactamase inhibitor combinations (Piperacillin-Tazobactam) [1].

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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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