Infectious Diseases Practice Questions

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)**.

Q: A 25-year-old farmer presented with a history of high-grade fever for 7 days and altered sensorium for 2 days. On examination, he was comatose and had conjunctival hemorrhage. Urgent investigations showed a hemoglobin of 11 gm/dl, serum bilirubin 8 mg/dl, and urea 78 mg/dl. The peripheral blood smear was negative for malarial parasites. What is the most likely diagnosis?

Weil's disease. ### Explanation The clinical presentation of high-grade fever, jaundice (bilirubin 8 mg/dl), and renal impairment (urea 78 mg/dl) in a farmer constitutes the classic triad of **Weil’s disease**, the severe icteric form of **Leptospirosis**. **1. Why Weil’s Disease is Correct:** Leptospirosis is a zoonosis caused by *Leptospira interrogans*, often transmitted via water contaminated with the urine of infected rodents (common in farmers). * **Clinical Triad:** Jaundice, renal failure, and hemorrhage (e.g., conjunctival suffusion/hemorrhage). * **Neurological Involvement:** Altered sensorium in this patient suggests aseptic meningitis or encephalopathy, common in severe cases. * **Laboratory Findings:** The negative malarial smear helps rule out cerebral malaria, which is the primary differential for fever with jaundice and altered sensorium. **2. Why Other Options are Incorrect:** * **Brucellosis:** Typically presents as undulant fever with musculoskeletal symptoms (back pain, arthritis) and hepatosplenomegaly, but rarely causes acute jaundice or renal failure. * **Acute Viral Hepatitis:** While it causes high bilirubin and altered sensorium (hepatic encephalopathy), it does not typically cause renal failure or conjunctival hemorrhage. * **Q Fever:** Caused by *Coxiella burnetii*, it usually presents as atypical pneumonia or culture-negative endocarditis; it does not typically present with this severe ictero-hemorrhagic profile. **3. High-Yield Pearls for NEET-PG:** * **Gold Standard Test:** Microscopic Agglutination Test (MAT). * **Culture Media:** EMJH medium or Fletcher’s medium. * **Morphology:** Spiral-shaped bacteria with "hooked ends" (Question-mark shape). * **Drug of Choice:** Doxycycline (prophylaxis/mild cases) or IV Penicillin G (severe cases). * **Key Sign:** Conjunctival suffusion (redness without inflammatory exudate) is a pathognomonic sign.

Q: Scrub typhus presents with which of the following clinical features?

Lymphadenopathy, rash, and eschar. **Explanation:** Scrub typhus is caused by **_Orientia tsutsugamushi_**, an obligate intracellular bacterium transmitted by the bite of the larval stage (chigger) of **trombiculid mites**. **Why Option A is correct:** The clinical presentation of Scrub typhus is characterized by a classic triad: 1. **Eschar:** This is the hallmark of the disease. It is a painless, necrotic, black crusty lesion that develops at the site of the mite bite. It is most commonly found in areas with skin folds (axilla, groin, neck). 2. **Lymphadenopathy:** Localized lymphadenopathy near the eschar site is common, which often progresses to generalized lymphadenopathy. 3. **Rash:** A maculopapular rash typically appears on the trunk around the 5th to 7th day of illness and spreads to the extremities (centrifugal spread). **Why other options are incorrect:** * **Options B, C, and D** are incorrect because they exclude one or more components of the classic clinical triad. While not every patient presents with all three features (the eschar is found in roughly 50-80% of cases), for the purpose of NEET-PG, the presence of **lymphadenopathy, rash, and eschar** defines the characteristic clinical profile of Scrub typhus. **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** Trombiculid mite (Leptotrombidium). * **Reservoir:** Mites (via transovarial transmission). * **Diagnosis:** **Weil-Felix test** shows agglutination with **OX-K** strain (OX-19 and OX-2 are negative). The gold standard is the Indirect Immunofluorescence Assay (IFA). * **Drug of Choice:** **Doxycycline** is the first-line treatment; Azithromycin is used in pregnancy. * **Differential:** Unlike Epidemic typhus (centripetal rash), Scrub typhus rash is centrifugal and involves an eschar.

Q: A person presents with difficulty of breathing and a CD-4 count of 200. What is the most probable diagnosis?

Pneumocystis pneumonia. **Explanation:** The clinical presentation of dyspnea in an immunocompromised patient with a **CD4 count of 200 cells/mm³** strongly points toward **Pneumocystis pneumonia (PCP)**, caused by *Pneumocystis jirovecii*. **Why Pneumocystis pneumonia is correct:** PCP is the most common opportunistic infection in patients with HIV when the CD4 count falls below **200 cells/mm³** [1]. It typically presents with a subacute onset of progressive dyspnea, non-productive cough, and low-grade fever. A hallmark feature is **exertional desaturation** (hypoxia out of proportion to radiologic findings). **Analysis of Incorrect Options:** * **Tuberculosis (A):** While common in HIV, TB can occur at **any CD4 count**. However, at CD4 >200, it usually presents with typical cavitary lesions. PCP is the more "classic" association specifically at the 200 threshold [1]. * **Histoplasmosis (B):** This fungal infection usually occurs when the CD4 count drops below **150 cells/mm³**. It often presents with systemic features like hepatosplenomegaly or lymphadenopathy. * **Candidiasis (C):** Mucocutaneous candidiasis (thrush) occurs at CD4 <250, but **Esophageal Candidiasis** (an AIDS-defining illness) typically occurs at CD4 <100. It presents with odynophagia rather than primary respiratory distress. **High-Yield Clinical Pearls for NEET-PG:** * **Investigation of Choice:** Induced sputum or Bronchoalveolar Lavage (BAL) with **Gomori Methenamine Silver (GMS)** stain showing "crushed ping-pong ball" cysts [1]. * **Radiology:** Characterized by bilateral perihilar **"ground-glass opacities."** * **Treatment:** High-dose **Trimethoprim-Sulfamethoxazole (TMP-SMX)** [1]. * **Steroid Indication:** Add corticosteroids if $PaO_2 35$ mmHg to prevent inflammatory worsening [1]. * **Prophylaxis:** Started when CD4 count is **< 200 cells/mm³**.

Q: All are risk factors for antituberculosis treatment related hepatotoxicity, EXCEPT?

HBeAg negative hepatitis B. Antituberculosis therapy (ATT)-induced hepatotoxicity is a common and potentially serious adverse effect, primarily associated with Isoniazid (INH), Rifampicin, and Pyrazinamide. [1] **Why HBeAg negative hepatitis B is the correct answer:** While chronic viral hepatitis (HBV and HCV) is a well-established risk factor for ATT-induced liver injury, the risk is specifically associated with **chronic carriers** or those with **active viral replication**. HBeAg (Hepatitis B e-antigen) is a marker of high viral replication and infectivity. Being "HBeAg negative" typically implies a lower viral load and lower replication state (unless it is a precore mutant), making it a less significant risk factor compared to active hepatitis or other systemic factors. [2] **Analysis of Incorrect Options:** * **CYP2E1 status:** Polymorphisms in the Cytochrome P450 2E1 gene (especially the c1/c1 genotype) are linked to increased production of hepatotoxic metabolites of INH, significantly increasing risk. * **HLA haplotype associations:** Genetic predisposition plays a major role. Specific HLA alleles (e.g., HLA-B*52, HLA-DQA1*0102, and HLA-DQB1*0502) have been strongly associated with an increased susceptibility to ATT-induced hepatotoxicity. * **Female gender:** Epidemiological studies consistently show that females are at a higher risk for developing drug-induced liver injury (DILI) from ATT compared to males. **High-Yield Clinical Pearls for NEET-PG:** * **Most hepatotoxic drug:** Pyrazinamide (PZA) > Isoniazid (INH) > Rifampicin (RIF). * **Other Risk Factors:** Age >35 years, malnutrition (low albumin), chronic alcohol consumption, and "Slow Acetylator" status (NAT2 polymorphism). * **Management Rule:** Discontinue ATT if Serum Bilirubin >1.5 mg/dL or if Transaminases are >3 times the upper limit of normal (with symptoms) or >5 times (if asymptomatic). [1]

Question 1

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

Question 2

What are the known complications of Shigella infections?

Accepted Answer

Hemolytic Uremic Syndrome (HUS), Reactive arthritis, and Sepsis

Answer

Hemolytic Uremic Syndrome (HUS) and Reactive arthritis

Answer

Reactive arthritis and Sepsis

Answer

Hemolytic Uremic Syndrome (HUS) and Sepsis

Question 3

A 25-year-old farmer presented with a history of high-grade fever for 7 days and altered sensorium for 2 days. On examination, he was comatose and had conjunctival hemorrhage. Urgent investigations showed a hemoglobin of 11 gm/dl, serum bilirubin 8 mg/dl, and urea 78 mg/dl. The peripheral blood smear was negative for malarial parasites. What is the most likely diagnosis?

Accepted Answer

Weil's disease

Answer

Brucellosis

Answer

Acute viral hepatitis

Answer

Q fever

Question 4

In which of the following conditions is the pneumococcal vaccine indicated?

Accepted Answer

HIV infection

Answer

Patients who have undergone splenectomy

Answer

Sickle cell anemia

Answer

Corticosteroid therapy

Question 5

A 35-year-old man presents with an 18 kg weight loss over the preceding 4 months. He reports no dieting, but experiences abdominal pain, nausea, and diarrhea. He also has a chronic cough. Sputum studies reveal Pneumocystis carinii, and esophagogastroduodenoscopy with biopsy shows Candida and Herpes in the esophagus. Which group of viruses is the causative agent of this patient's underlying disease?

Accepted Answer

Retroviridae

Answer

Caliciviridae

Answer

Coronaviridae

Answer

Flaviviridae

Question 6

Scrub typhus presents with which of the following clinical features?

Accepted Answer

Lymphadenopathy, rash, and eschar

Answer

Lymphadenopathy and rash but no eschar

Answer

Rash and eschar but no lymphadenopathy

Answer

Lymphadenopathy but no rash and eschar

Question 7

Which of the following infections does NOT typically cause acute hepatic and renal failure?

Accepted Answer

Shigellosis

Answer

Leptospirosis

Answer

Malaria

Answer

Hantavirus

Question 8

A person presents with difficulty of breathing and a CD-4 count of 200. What is the most probable diagnosis?

Accepted Answer

Pneumocystis pneumonia

Answer

Tuberculosis

Answer

Histoplasmosis

Answer

Candidiasis

Question 9

Following extraction of an upper central incisor, a patient develops ophthalmoplegia, meningitis, and lateral rectus paralysis. What is the most likely diagnosis?

Accepted Answer

Cavernous sinus thrombosis

Answer

Not related

Answer

Cellulitis

Answer

Ludwig's angina

Question 10

All are risk factors for antituberculosis treatment related hepatotoxicity, EXCEPT?

Accepted Answer

HBeAg negative hepatitis B

Answer

CYP2E1 status

Answer

HLA haplotype associations

Answer

Female gender

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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