Infectious Diseases Practice Questions

Q: What is the drug of choice in herpes simplex encephalitis?

Acyclovir. **Explanation:** **Acyclovir** is the gold-standard drug of choice for Herpes Simplex Encephalitis (HSE). HSE is a medical emergency, most commonly caused by HSV-1 in adults. Acyclovir acts as a nucleoside analog that inhibits viral DNA polymerase [1]. It is administered intravenously (10 mg/kg every 8 hours for 14–21 days) [1]. Early initiation is critical because it significantly reduces mortality (from 70% to ~20-30%) and improves neurological outcomes. **Why other options are incorrect:** * **Vidarabine:** This was the previous standard of care before the 1980s. However, it is less effective and significantly more toxic (bone marrow suppression, neurotoxicity) compared to Acyclovir. * **Interferon:** While interferons have antiviral properties and are used in chronic hepatitis, they have no proven efficacy in the acute management of HSE. * **Amantadine:** This is an anti-influenza A medication (M2 ion channel blocker) and is also used in Parkinson’s disease. It has no activity against the Herpesviridae family. **High-Yield Clinical Pearls for NEET-PG:** * **Site of involvement:** HSE characteristically affects the **temporal lobes** (look for "hemorrhagic necrosis" on pathology) [2]. * **Gold Standard Diagnosis:** **CSF PCR** for HSV DNA (highest sensitivity and specificity). * **EEG Finding:** Periodic lateralized epileptiform discharges (**PLEDs**) over the temporal lobes. * **MRI:** The most sensitive imaging modality, showing hyperintensities in the temporal lobes and insular cortex on T2/FLAIR sequences. * **Empiric Therapy:** Never delay Acyclovir while waiting for diagnostic confirmation if HSE is suspected.

Q: Atypical chest X-ray findings in tuberculosis are usually seen in which of the following populations?

Patients with HIV. **Explanation:** The presentation of Pulmonary Tuberculosis (PTB) on a chest X-ray (CXR) is heavily dependent on the host's immune status. In immunocompetent adults, **Post-Primary (Reactivation) TB** typically presents with "typical" findings: upper lobe infiltrates and cavitary lesions. **1. Why HIV is the correct answer:** In patients with HIV, the radiological presentation depends on the degree of immunosuppression (CD4 count). [1] As the CD4 count declines, the body loses the ability to form granulomas and contain the infection. This leads to **"atypical" findings**, which resemble primary TB rather than reactivation TB. These include: * Lower or middle lobe opacities (instead of upper lobes). * Intrathoracic lymphadenopathy (hilar/mediastinal). * Miliary patterns. * **Absence of cavitation** (cavitation is an immune-mediated necrotic process; low immunity prevents its formation). [1] * Normal CXR (seen in up to 10-15% of symptomatic HIV patients). **2. Why other options are incorrect:** * **MDR-TB:** The drug resistance profile of the *M. tuberculosis* strain does not inherently change the radiological pattern; it affects treatment response. * **Adults with TB:** Most adults present with "typical" reactivation TB (upper lobe cavitary disease) unless they are severely immunocompromised. * **Culture-positive TB:** This simply confirms the diagnosis and does not dictate the radiological morphology. **High-Yield Clinical Pearls for NEET-PG:** * **CD4 >200/mm³:** CXR often shows typical post-primary patterns (cavitation). [1] * **CD4 <200/mm³:** CXR shows atypical patterns (adenopathy, no cavities, lower lobe involvement). [1] * **Most common CXR finding in Primary TB:** Hilar lymphadenopathy. * **Ghon’s Complex:** Calcified peripheral node + calcified hilar node (Ranke complex).

Q: A patient with necrotizing fasciitis was treated with antibiotics and debridement and discharged on wound recovery. He presented 10 days later with diarrhea and fever. Which of the following investigations or interventions is NOT indicated?

Continue the same antibiotic. The clinical presentation of fever and diarrhea following recent broad-spectrum antibiotic therapy for necrotizing fasciitis is highly suggestive of **Clostridioides difficile Infection (CDI)** [1]. **Why "Continue the same antibiotic" is NOT indicated:** The primary step in managing CDI is the immediate cessation of the inciting antibiotic agent whenever possible. Continuing the same antibiotic further disrupts the normal colonic flora, allowing *C. difficile* to proliferate and produce toxins, thereby worsening the clinical condition. **Analysis of other options:** * **Stop loperamide:** Anti-motility agents like loperamide are contraindicated in CDI as they can precipitate toxic megacolon by slowing the clearance of toxins from the bowel. * **Oral Vancomycin:** According to current guidelines (IDSA/SHEA), oral Vancomycin (or Fidaxomicin) is the first-line treatment for CDI [2]. Intravenous vancomycin is ineffective as it does not reach therapeutic concentrations in the gut lumen. * **Hand Hygiene:** *C. difficile* produces spores that are resistant to alcohol-based sanitizers. **Mechanical handwashing with soap and water** is mandatory to physically remove spores and prevent nosocomial transmission. Therefore, the statement that alcohol sanitizers are superior is false (making it a potential distractor, though in this specific question format, stopping the offending drug is the most critical clinical intervention). **Clinical Pearls for NEET-PG:** * **Risk Factors:** Recent antibiotic use (Clindamycin, Fluoroquinolones, Cephalosporins), PPI use, and hospitalization [2]. * **Diagnosis:** Stool toxin assay (GDH/EIA) or PCR for toxin genes [1]. * **Complication:** Pseudomembranous colitis (visualized as yellow-white plaques on colonoscopy) [1]. * **Treatment:** Oral Vancomycin 125 mg QID for 10 days [2]. For fulminant cases, use high-dose oral Vancomycin plus IV Metronidazole.

Q: Which of the following is pathognomonic of miliary tuberculosis?

Choroid tubercles on fundus examination. **Explanation:** **Miliary Tuberculosis (TB)** is a form of disseminated tuberculosis resulting from the hematogenous spread of *Mycobacterium tuberculosis* [1]. **Why Option B is Correct:** **Choroid tubercles** are considered **pathognomonic** of miliary TB [1]. These are small, yellowish-white, granulomatous lesions with ill-defined margins, typically seen on funduscopic examination. They represent direct hematogenous seeding of the choroid plexus. Their presence is highly specific; when seen in a patient with systemic symptoms, they confirm the diagnosis of miliary TB even before radiological or microbiological evidence is available. They are found in approximately 10–30% of cases. **Analysis of Incorrect Options:** * **Option A (Snow storm appearance):** While a "millet-seed" or "snow storm" appearance on Chest X-ray (CXR) is a classic finding of miliary TB, it is **not pathognomonic** [1]. Similar radiological patterns can be seen in silicosis, sarcoidosis, histoplasmosis, or metastatic deposits (e.g., thyroid or renal cell carcinoma). * **Options C & D (Pericardial and Peritoneal TB):** These are forms of extrapulmonary tuberculosis [2]. While they can occur concurrently with miliary spread, they are distinct clinical entities and do not serve as diagnostic hallmarks for miliary dissemination. **Clinical Pearls for NEET-PG:** * **Gold Standard Diagnosis:** Sputum/body fluid culture or biopsy showing caseating granulomas. * **Most Sensitive Imaging:** High-Resolution CT (HRCT) is more sensitive than CXR for detecting early miliary nodules (1–2 mm). * **Hematological finding:** Leukopenia or leukemoid reaction can occur; hyponatremia (due to SIADH or adrenal involvement) is common. * **Anergetic response:** Up to 50% of patients with miliary TB may have a **negative Tuberculin Skin Test (Mantoux)** due to overwhelmed immunity.

Q: All of the following should be included during the preliminary evaluation of a case of suspected acute viral hepatitis, except?

IgM antibody to Hepatitis B e antigen (IgM anti-HBe). Explanation: In the preliminary evaluation of acute viral hepatitis, the goal is to identify the specific viral etiology (A, B, C, or E) using markers that appear during the acute phase of infection [1]. Why Option D is the Correct Answer: IgM anti-HBe is not a standard clinical marker used in the diagnosis of acute hepatitis. While HBeAg (Hepatitis B e-antigen) indicates high viral replication and infectivity, the antibodies to it (Anti-HBe) typically appear during the "seroconversion" phase as HBeAg disappears. There is no clinical utility for an IgM-specific version of this antibody in routine diagnostic panels; its presence does not help differentiate acute from chronic infection or guide initial management. Analysis of Incorrect Options: * A. HBsAg: This is the first serological marker to appear in Hepatitis B [1]. It indicates the presence of the virus but cannot distinguish between acute infection and a chronic carrier state [1]. * B. IgM anti-HBc: This is the gold standard for diagnosing acute Hepatitis B [1]. It is particularly crucial during the "window period" when HBsAg may have disappeared but Anti-HBs has not yet appeared [1]. * C. Anti-HCV: This is the primary screening test for Hepatitis C. While it may take weeks to become positive (leading to a potential false negative in the very early acute phase), it remains a standard part of the initial workup for viral hepatitis. High-Yield Clinical Pearls for NEET-PG: * Best marker for acute HBV: IgM anti-HBc [1]. * Best marker for chronic HBV: HBsAg persisting for >6 months [1]. * Window Period: The interval where only IgM anti-HBc is detectable [1]. * Acute Hepatitis A/E: Diagnosed by IgM anti-HAV and IgM anti-HEV, respectively [1]. * HBeAg: Indicates high infectivity and active viral replication ("e" for envelope/extracellular) [1].

Q: What is the drug of choice for acute Salmonella Typhi infection?

Cefixime. ### Explanation The management of Enteric Fever (Typhoid) has evolved significantly due to the emergence of drug-resistant strains. **Why Cefixime is the Correct Answer:** Currently, **Third-generation Cephalosporins** (Ceftriaxone IV or Cefixime orally) are considered the **drugs of choice** for the empirical treatment of acute *Salmonella Typhi* infection. This shift is primarily due to the widespread prevalence of **Multidrug-Resistant (MDR)** strains (resistant to Chloramphenicol, Ampicillin, and Cotrimoxazole) and the increasing incidence of **Fluoroquinolone-resistant** *S. Typhi* (NARST - Nalidixic Acid Resistant *Salmonella Typhi*). Cefixime is preferred for outpatient management of uncomplicated cases. **Analysis of Incorrect Options:** * **Chloramphenicol (A):** Historically the gold standard, it is no longer the first-line choice due to high rates of plasmid-mediated resistance (MDR strains) and the risk of bone marrow toxicity (Aplastic anemia). * **Ciprofloxacin (B):** Previously the drug of choice, it is now avoided as primary empirical therapy in South Asia because of high "Minimum Inhibitory Concentrations" (MICs) and widespread resistance (NARST). It is now reserved for documented sensitive cases. * **Amoxicillin (D):** Like Chloramphenicol, it is part of the traditional "first-line" drugs but is currently ineffective against MDR strains. **Clinical Pearls for NEET-PG:** * **Drug of Choice for Carriers:** **Amoxicillin** is used for biliary carriers; **Ciprofloxacin** is used for fecal carriers. * **Most sensitive test:** Bone marrow culture (remains positive even after starting antibiotics). * **Standard Diagnostic:** Blood culture is the gold standard in the 1st week; Widal test is significant only from the 2nd week onwards. * **Azithromycin:** Often used as an alternative for uncomplicated typhoid caused by quinolone-resistant strains.

Q: A 20-year-old female diagnosed with acute myeloid leukemia underwent allogeneic stem cell transplantation one year ago. During a follow-up visit, she presents with manifestations of chronic graft-versus-host disease but is otherwise doing well and has no evidence of recurrence. Which of the following vaccines should not be administered to this patient at this point in time?

Measles, mumps, and rubella. **Explanation** The core concept tested here is the contraindication of **live-attenuated vaccines** in immunocompromised individuals. **1. Why "Measles, mumps, and rubella (MMR)" is the correct answer:** MMR is a live-attenuated vaccine. In patients who have undergone Hematopoietic Stem Cell Transplantation (HSCT), live vaccines are strictly contraindicated for at least **24 months** post-transplant. Furthermore, they should only be administered if the patient is free of **Graft-versus-Host Disease (GvHD)** and has been off all immunosuppressive therapy for at least 3–11 months. This patient has active chronic GvHD, making the administration of a live vaccine highly dangerous due to the risk of unchecked viral replication. **2. Why the other options are incorrect:** * **A & D (Diphtheria-tetanus and IPV):** These are **inactivated/killed vaccines** (or toxoids). Inactivated vaccines do not pose a safety risk of causing disease in immunocompromised hosts. Post-HSCT protocols typically recommend restarting the primary series of these vaccines 6–12 months after transplantation. * **B (23-Valent pneumococcal polysaccharide):** This is a subunit/polysaccharide vaccine. It is not live and is actually a high-priority vaccine for HSCT recipients to prevent invasive pneumococcal disease, usually administered starting 6–12 months post-transplant. **Clinical Pearls for NEET-PG:** * **HSCT Rule:** Inactivated vaccines start at **6 months** post-transplant; Live vaccines start at **24 months** (only if no GvHD). * **GvHD Status:** Active GvHD is a definitive contraindication for live vaccines, regardless of the time elapsed since transplant. * **Household Contacts:** Family members of immunocompromised patients *should* receive MMR and Varicella vaccines (to provide herd immunity), but should avoid the Oral Polio Vaccine (OPV) as the virus can be shed in stools. Always prefer **Inactivated Polio Vaccine (IPV)**.

Question 1

What is the drug of choice in herpes simplex encephalitis?

Accepted Answer

Acyclovir

Answer

Vidarabine

Answer

Interferon

Answer

Amantadine

Question 2

Which of the following statements is NOT true about the clinical course of chickenpox?

Accepted Answer

Younger children tend to have more vesicles than elders.

Answer

Skin rash is maculopapular and vesicular in various stages of development.

Answer

Secondary and tertiary cases in the family tend to have a relatively larger number of vesicles.

Answer

Immunocompromised hosts have a higher chance of visceral complications.

Question 3

Atypical chest X-ray findings in tuberculosis are usually seen in which of the following populations?

Accepted Answer

Patients with HIV

Answer

Multidrug-resistant tuberculosis (MDR TB)

Answer

Adults with tuberculosis (TB)

Answer

Culture-positive tuberculosis (TB)

Question 4

A patient with necrotizing fasciitis was treated with antibiotics and debridement and discharged on wound recovery. He presented 10 days later with diarrhea and fever. Which of the following investigations or interventions is NOT indicated?

Accepted Answer

Continue the same antibiotic

Answer

Stop loperamide

Answer

Oral Vancomycin is the drug of choice

Answer

Washing hands with alcohol-based hand sanitizers is superior to washing hands with soap to stop the spread of diarrhea.

Question 5

Which of the following is pathognomonic of miliary tuberculosis?

Accepted Answer

Choroid tubercles on fundus examination

Answer

Snow storm appearance in CXR

Answer

Pericardial TB

Answer

Peritoneal TB

Question 6

All of the following should be included during the preliminary evaluation of a case of suspected acute viral hepatitis, except?

Accepted Answer

IgM antibody to Hepatitis B e antigen (IgM anti-HBe)

Answer

Hepatitis B surface antigen (HBsAg)

Answer

IgM antibody to Hepatitis B core antigen (IgM anti-HBc)

Answer

Antibody to Hepatitis C virus (Anti-HCV)

Question 7

What is the drug of choice for acute Salmonella Typhi infection?

Accepted Answer

Cefixime

Answer

Chloramphenicol

Answer

Ciprofloxacin

Answer

Amoxicillin

Question 8

A 35-year-old HIV-positive man presents with a 6-month history of progressive memory loss and incontinence. He is currently on zidovudine and a protease inhibitor. Examination reveals deficits in cognitive and fine motor control functions. His CD4 cell count is 25/mm
3. MRI studies show moderate brain atrophy with no focal lesions. Lumbar puncture shows no cerebrospinal fluid abnormalities. What is the most likely diagnosis?

Accepted Answer

HIV encephalitis

Answer

CMV encephalitis

Answer

Cryptococcal meningoencephalitis

Answer

HIV myelopathy

Question 9

Which variant of immunoblastic lymphoma is primarily seen in HIV patients?

Accepted Answer

Primary Effusion Lymphoma

Answer

Centroblastic Lymphoma

Answer

Anaplastic Lymphoma

Answer

Any of the Above

Question 10

A 20-year-old female diagnosed with acute myeloid leukemia underwent allogeneic stem cell transplantation one year ago. During a follow-up visit, she presents with manifestations of chronic graft-versus-host disease but is otherwise doing well and has no evidence of recurrence. Which of the following vaccines should not be administered to this patient at this point in time?

Accepted Answer

Measles, mumps, and rubella

Answer

Diphtheria-tetanus

Answer

23-Valent pneumococcal polysaccharide

Answer

Poliomyelitis injection

Infectious Diseases — MCQs

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