Infectious Diseases Practice Questions

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, the patient was comatose and had conjunctival hemorrhage. Urgent investigations showed a hemoglobin of 11 gm/dl, serum bilirubin of 8 mg/dl, and urea of 78 mg/dl. Peripheral blood smear was negative for malarial parasites. What is the most likely diagnosis?

Weil's disease. The clinical presentation of high-grade fever, **conjunctival suffusion (hemorrhage)**, jaundice (elevated bilirubin), and renal dysfunction (elevated urea) in a farmer strongly suggests **Weil’s disease**, the severe form of **Leptospirosis** [1]. **Why Weil’s Disease is Correct:** Leptospirosis is a zoonotic infection caused by *Leptospira interrogans*, often transmitted via water contaminated with animal urine (common in farmers) [1]. Weil’s disease is characterized by the classic triad of **jaundice, renal failure, and hemorrhage**. Conjunctival suffusion is a pathognomonic sign. The altered sensorium in this patient likely stems from uremia or hepatic involvement [1]. The negative malaria smear helps rule out cerebral malaria, which is the primary differential [2]. **Why Other Options are Incorrect:** * **Brucellosis:** Typically presents as a chronic, undulant fever with musculoskeletal symptoms (sacroiliitis) and hepatosplenomegaly, but rarely causes acute renal failure or conjunctival hemorrhage. * **Acute Viral Hepatitis:** While it causes high bilirubin and altered sensorium (hepatic encephalopathy), it does not typically cause acute renal failure (urea 78 mg/dl) or conjunctival hemorrhage early in the course. * **Q Fever:** Caused by *Coxiella burnetii*, it usually presents as an atypical pneumonia or culture-negative endocarditis; it does not typically present with this specific icterohemorrhagic triad. **High-Yield Pearls for NEET-PG:** * **Pathognomonic Sign:** Conjunctival suffusion (redness without inflammatory exudate). * **Gold Standard Test:** Microscopic Agglutination Test (MAT) [2]. * **Drug of Choice:** Doxycycline (mild cases) or IV Penicillin G (severe cases). * **Biphasic Nature:** Leptospiremic phase (first week) followed by the Immune phase (second week).

Q: A 42-year-old male presented with high-grade fever and hepatosplenomegaly. On evaluation, a skin lesion suggestive of eschar was noticed on the thigh. The patient was diagnosed with scrub typhus. What is the best treatment for this condition?

Oral Doxycycline. ### Explanation **Correct Answer: A. Oral Doxycycline** **Medical Concept:** Scrub typhus is caused by the obligate intracellular bacterium ***Orientia tsutsugamushi***, transmitted by the bite of larval trombiculid mites (chiggers). The clinical hallmark is an **eschar** at the site of the bite, accompanied by fever, headache, and lymphadenopathy. Because the pathogen is an intracellular organism, the treatment of choice must be a drug with excellent intracellular penetration. **Doxycycline** (a tetracycline) is the gold standard treatment for scrub typhus in both adults and children. It inhibits bacterial protein synthesis by binding to the 30S ribosomal subunit. **Analysis of Incorrect Options:** * **B. Oral Erythromycin:** While macrolides (like Azithromycin) are effective alternatives—especially in pregnancy or for doxycycline-resistant strains—Erythromycin is not the first-line agent due to a higher side-effect profile and lower efficacy compared to Doxycycline or Azithromycin. * **C. IV Ceftriaxone:** This is a third-generation cephalosporin that acts on the bacterial cell wall. Since *Orientia* is an intracellular pathogen and lacks a traditional peptidoglycan layer, beta-lactams are entirely ineffective. * **D. IV Gentamicin:** Aminoglycosides are ineffective against intracellular rickettsial-like organisms and are generally reserved for Gram-negative aerobic infections (e.g., Tularemia or Plague) [1]. **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** Larval stage of Trombiculid mite (Chigger). * **Diagnostic Test:** **Weil-Felix test** (Heterophile antibody test) shows agglutination with **OX-K** strain. The gold standard is the Indirect Immunofluorescence Assay (IFA). * **Drug of Choice in Pregnancy:** **Azithromycin** is preferred over Doxycycline. * **The "Doxy-Response":** Patients with scrub typhus typically show dramatic clinical improvement (defervescence) within 24–48 hours of starting Doxycycline.

Q: An 18-year-old woman presents with 3 weeks of malaise, 2 weeks of fever, and a sore throat. Physical examination reveals pharyngeal infection with enlarged tonsils and a patchy, white exudate; enlarged, palpable anterior and posterior cervical, axillary, and inguinal lymph nodes; tenderness in the right upper quadrant; and minimal splenomegaly. Laboratory data show hemoglobin 14 g/dL; hematocrit 42%; platelets 380,000/mL; WBC 8500/mL, with 35% segmented neutrophils, 1% eosinophils, and 64% lymphocytes, of which 36% were atypical. Which of the following is the most likely diagnosis?

infectious mononucleosis. **Explanation:** The clinical presentation is a classic description of **Infectious Mononucleosis (IM)**, typically caused by the **Epstein-Barr Virus (EBV)**. The diagnosis is based on the clinical triad of **fever, pharyngitis, and lymphadenopathy** (characteristically involving the posterior cervical nodes). **Why Option C is correct:** The patient exhibits systemic lymphadenopathy (cervical, axillary, and inguinal) and splenomegaly. The laboratory findings are definitive: a relative and absolute **lymphocytosis** with a high percentage of **atypical lymphocytes** (Downey cells) [1]. These are activated T-cells responding to EBV-infected B-cells. The RUQ tenderness suggests mild hepatitis, which occurs in approximately 90% of IM cases [1]. **Why other options are incorrect:** * **A. Infectious Hepatitis:** While RUQ tenderness and malaise occur, hepatitis does not typically present with exudative pharyngitis or significant atypical lymphocytosis. * **B. Lymphocytic Leukemia:** While it causes lymphadenopathy and lymphocytosis, the cells would be "blasts" or malignant cells rather than reactive atypical lymphocytes. The normal hemoglobin and platelet counts make acute leukemia unlikely. * **D. Hodgkin’s Disease:** This usually presents with painless, "rubbery" lymphadenopathy (often mediastinal) and lacks the acute onset of exudative pharyngitis and high-grade atypical lymphocytosis [1]. **NEET-PG High-Yield Pearls:** * **Heterophile Antibody Test (Monospot):** The initial screening test of choice. * **Atypical Lymphocytes:** Defined as >10% of the total WBC count in IM. * **Ampicillin/Amoxicillin Rash:** If these antibiotics are mistakenly given for the sore throat, a maculopapular rash often develops. * **Complication:** Splenic rupture is a rare but serious risk; patients must avoid contact sports for 3–4 weeks.

Q: In dengue infection, what is the expected number of petechial spots per square inch in the cubital fossa?

>20. This question pertains to the **Hess Test** (also known as the **Tourniquet Test**), a clinical diagnostic tool used to assess capillary fragility and a key criterion in the WHO classification of Dengue Hemorrhagic Fever (DHF). ### **Explanation of the Correct Answer** The correct answer is **>20 (Option D)**. According to the WHO guidelines for the management of Dengue, a tourniquet test is considered **positive** if **20 or more petechiae** are observed per 1 square inch (6.25 cm²) area, usually on the volar aspect of the forearm or the cubital fossa. **The Procedure:** 1. Inflate a blood pressure cuff to a point midway between the systolic and diastolic pressures (Mean Arterial Pressure). 2. Maintain this pressure for 5 minutes. 3. Deflate and wait 2 minutes for skin color to return to normal. 4. Count the number of petechiae in a 1-inch square area. ### **Analysis of Incorrect Options** * **Options A, B, and C (>5, >10, >15):** These values are below the standardized diagnostic threshold. While any petechiae indicate some degree of capillary fragility, they do not meet the specific WHO criteria for a "positive" test in the context of Dengue. ### **High-Yield Clinical Pearls for NEET-PG** * **Significance:** A positive tourniquet test suggests **capillary fragility** and **thrombocytopenia**. It is often the only hemorrhagic manifestation in the early stages of Dengue. * **WHO Criteria:** It is one of the four clinical components required for the diagnosis of DHF (along with fever, hemorrhagic tendencies, and plasma leakage). * **Sensitivity:** The test has high specificity but variable sensitivity; a negative test does **not** rule out Dengue. * **Dengue Triad:** Fever, rash, and severe body ache ("Break-bone fever"). * **Vector:** *Aedes aegypti* (Daytime biter, breeds in artificial collections of clean water).

Q: A 36-year-old female presented with fever (105°F) and leukocytosis (15,000/mm³). She also complained of vomiting and diarrhea. She had eaten fried rice at a Chinese restaurant and became ill four days after her menstrual period. She had retained a vaginal tampon. What is the diagnosis?

Toxic Shock Syndrome. ### Explanation **Correct Answer: B. Toxic Shock Syndrome (TSS)** The clinical presentation of high fever, gastrointestinal symptoms (vomiting/diarrhea), and leukocytosis in a female with a history of **retained vaginal tampons** is a classic "textbook" description of **Staphylococcal Toxic Shock Syndrome**. The underlying mechanism involves **TSST-1 (Toxic Shock Syndrome Toxin-1)**, produced by *Staphylococcus aureus*. TSST-1 acts as a **superantigen**, which bypasses normal antigen processing. It binds directly to the MHC Class II of antigen-presenting cells and the Vβ region of T-cell receptors. This leads to a massive, non-specific activation of T-cells and a "cytokine storm" (IL-1, IL-2, TNF-α, and IFN-γ), resulting in multi-organ dysfunction and shock. **Why other options are incorrect:** * **A. SSSS:** Caused by **Exfoliative toxins (A and B)**. It presents with diffuse erythema and skin peeling (Nikolsky sign positive), typically in neonates, not with the systemic GI symptoms and tampon history described. * **C. Staphylococcal food poisoning:** Caused by **Enterotoxins (A-E)**. While the patient ate fried rice (usually associated with *Bacillus cereus*), staphylococcal food poisoning has a very short incubation (1–6 hours) and does not typically cause high fever or leukocytosis. * **D. Waterhouse-Friderichsen syndrome:** Characterized by adrenal hemorrhage and circulatory collapse secondary to *Neisseria meningitidis* septicemia. **NEET-PG High-Yield Pearls:** * **Superantigens:** TSST-1, Staphylococcal Enterotoxins, and Streptococcal Pyrogenic Exotoxin (SpeA/C). * **CDC Criteria for TSS:** Fever >38.9°C, Hypotension, Diffuse macular erythroderma (sunburn-like rash), Desquamation (1–2 weeks after onset), and involvement of ≥3 organ systems. * **Fried Rice Association:** Classically associated with *Bacillus cereus* (emetic toxin), but the tampon history here is the "pathognomonic" distractor/clue for TSS.

Question 1

A 25-year-old farmer presented with a history of high-grade fever for 7 days and altered sensorium for 2 days. On examination, the patient was comatose and had conjunctival hemorrhage. Urgent investigations showed a hemoglobin of 11 gm/dl, serum bilirubin of 8 mg/dl, and urea of 78 mg/dl. 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 2

A 42-year-old male presented with high-grade fever and hepatosplenomegaly. On evaluation, a skin lesion suggestive of eschar was noticed on the thigh. The patient was diagnosed with scrub typhus. What is the best treatment for this condition?

Accepted Answer

Oral Doxycycline

Answer

Oral Erythromycin

Answer

IV Ceftriaxone

Answer

IV Gentamicin

Question 3

An 18-year-old woman presents with 3 weeks of malaise, 2 weeks of fever, and a sore throat. Physical examination reveals pharyngeal infection with enlarged tonsils and a patchy, white exudate; enlarged, palpable anterior and posterior cervical, axillary, and inguinal lymph nodes; tenderness in the right upper quadrant; and minimal splenomegaly. Laboratory data show hemoglobin 14 g/dL; hematocrit 42%; platelets 380,000/mL; WBC 8500/mL, with 35% segmented neutrophils, 1% eosinophils, and 64% lymphocytes, of which 36% were atypical. Which of the following is the most likely diagnosis?

Accepted Answer

infectious mononucleosis

Answer

infectious hepatitis

Answer

lymphocytic leukemia

Answer

Hodgkin's disease

Question 4

In dengue infection, what is the expected number of petechial spots per square inch in the cubital fossa?

Accepted Answer

>20

Answer

>5

Answer

>10

Answer

>15

Question 5

A patient with endocarditis develops a urinary tract infection (UTI) caused by Enterococcus faecium, which is resistant to ampicillin and gentamicin. What is the most clinically appropriate next step?

Accepted Answer

Consider vancomycin as an alternative treatment.

Answer

Determine if fluorescent microscopy is available for the diagnosis of actinomycosis.

Answer

No further clinical workup is needed.

Answer

Suggest to the laboratory that low colony counts may reflect infection.

Question 6

A patient tested positive for MTB on sputum CBNAAT. The patient did not return to the PHC despite multiple reminders. The patient now presents with non-massive hemoptysis and is alarmed. What is the next best step for this patient?

Accepted Answer

Perform CT scan of the chest

Answer

Urgent coagulation studies

Answer

Schedule a flexible fibreoptic bronchoscopy

Answer

Urgent rigid bronchoscopy with prophylactic balloon tamponade

Question 7

A 36-year-old female presented with fever (105°F) and leukocytosis (15,000/mm³). She also complained of vomiting and diarrhea. She had eaten fried rice at a Chinese restaurant and became ill four days after her menstrual period. She had retained a vaginal tampon. What is the diagnosis?

Accepted Answer

Toxic Shock Syndrome

Answer

Staphylococcal Scalded Skin Syndrome (SSSS)

Answer

Staphylococcal food poisoning

Answer

Waterhouse-Friderichsen syndrome

Question 8

A patient presents with lower gastrointestinal bleed. Sigmoidoscopy shows an ulcer in the sigmoid. Biopsy from this area shows flask-shaped ulcers. Which of the following is the most appropriate treatment?

Accepted Answer

Intravenous metronidazole

Answer

Intravenous ceftriaxone

Answer

Intravenous steroids and sulphasalazine

Answer

Hydrocortisone enemas

Question 9

All are true about Immune Reconstitution Inflammatory syndrome (IRIS) except?

Accepted Answer

It occurs when CD4 cell count is < 50 cells/mm3

Answer

Develops after initiation of anti-retroviral therapy

Answer

Associated with delayed type of hypersensitivity

Answer

Does not require a specific antimicrobial therapy for recovery

Question 10

An active intravenous drug abuser presents with a 5-day history of fever, a cough occasionally productive of blood, and pleuritic chest pain. Petechiae are present in his mouth and conjunctiva, and small linear hemorrhages are visible under his fingernails. Which of the following test results would MOST likely confirm the identity of the causative agent?

Accepted Answer

Blood culture of a coagulase-positive, catalase positive, gram-positive coccus

Answer

Antibodies to p24 capsid antigen

Answer

Antibodies to Trichinella spiralis antigen

Answer

Blood culture of a catalase-positive, novobiocin-sensitive, gram-positive coccus

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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