Infectious Diseases — MCQs

A 17-year-old man presents with fatigue, malaise, fever, and sore throat. He has no significant past medical history and is not on any medications. Physical examination reveals enlarged, palpable cervical lymph nodes. He reports no weight loss or night sweats. Laboratory investigations include a normal chest x-ray, negative throat swab, and an abnormal blood film with atypical lymphocytes. His hemoglobin is 15.5 g/dL; hematocrit 42%; platelets 290,000/mL; WBC 10,500/mL, with 45% segmented neutrophils, 1% eosinophils, and 54% lymphocytes, of which 36% were atypical. Which of the following is the most appropriate initial diagnostic test?

Q638Medium

Which of the following is NOT a feature of cerebral malaria?

Q639Medium

What is the recommended prophylaxis for a pinprick injury in an HIV-positive individual, EXCEPT for which of the following?

Q640Easy

What is the drug of choice for the treatment of latent syphilis?

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 631: What is a common cause of post-influenza pneumonia in a 70-year-old woman who developed flu and died one week after pneumonia?

A. Staphylococcus (Correct Answer)
B. Measles
C. Legionella
D. CMV

Explanation: ### Explanation **Correct Answer: A. Staphylococcus** **Medical Concept:** Post-influenza pneumonia is a classic example of **secondary bacterial pneumonia**. Influenza virus damages the respiratory epithelium and impairs ciliary clearance, creating a fertile environment for bacterial superinfection [1]. While *Streptococcus pneumoniae* is the most common cause of community-acquired pneumonia overall, **Staphylococcus aureus** is a notorious and high-yield cause specifically following an influenza infection [1]. It often presents with a rapid clinical decline, necrotizing features, or cavitary lesions on imaging. In elderly patients, this secondary infection is a leading cause of mortality approximately 1–2 weeks after the initial viral prodrome. **Analysis of Incorrect Options:** * **B. Measles:** While measles can cause primary viral pneumonia (Hecht’s giant cell pneumonia) or secondary bacterial pneumonia, it is not a complication of the influenza virus. * **C. Legionella:** This causes "atypical" pneumonia often associated with contaminated water sources (AC ducts, cooling towers) and presents with GI symptoms or hyponatremia [1]. It is not specifically linked to post-viral states. * **D. CMV:** Cytomegalovirus pneumonia typically occurs in severely immunocompromised patients (e.g., post-transplant or HIV/AIDS). It is not a standard complication of seasonal influenza in an otherwise immunocompetent elderly patient. **NEET-PG High-Yield Pearls:** * **Most common cause of secondary bacterial pneumonia post-flu:** *Streptococcus pneumoniae*. * **Most "characteristic" or "classic" cause post-flu:** *Staphylococcus aureus* (often MRSA) [1]. * **Clinical Clue:** Look for a "biphasic" illness pattern—the patient starts getting better from the flu, then suddenly develops high fever, productive cough, and respiratory distress [1]. * **Radiology:** *S. aureus* often presents with bilateral patchy infiltrates or **pneumatoceles** (air-filled cysts).

Question 632: Corticosteroids are absolutely contraindicated in which of the following types of tuberculosis?

A. Miliary
B. Meningeal
C. Intestinal (Correct Answer)
D. Renal

Explanation: **Explanation:** In the management of Tuberculosis (TB), corticosteroids are used as an adjuvant to anti-tubercular therapy (ATT) to reduce life-threatening inflammation and prevent complications like fibrosis or adhesions [1]. However, they are **absolutely contraindicated in Intestinal TB.** **Why Intestinal TB?** The primary concern in Intestinal TB is the risk of **bowel perforation**. Corticosteroids inhibit the healing process and mask signs of peritonitis. Since intestinal TB often involves ulceration of the Peyer's patches and thinning of the bowel wall, steroids can lead to "silent" perforation, which is a surgical emergency with high mortality. **Analysis of Other Options:** * **Meningeal TB (Option B):** This is a **strong indication** for steroids (e.g., Dexamethasone). They reduce cerebral edema, prevent basal arachnoiditis, and decrease the incidence of hydrocephalus and neurological deficits [1]. * **Miliary TB (Option A):** Steroids are often used as an adjunct, especially if there is associated adrenal insufficiency or severe respiratory distress (ARDS) to improve oxygenation and reduce the systemic inflammatory response. * **Renal TB (Option D):** Steroids are indicated specifically to prevent **ureteric strictures** and subsequent hydronephrosis during the healing phase of the disease. **High-Yield Clinical Pearls for NEET-PG:** * **Indications for Steroids in TB:** TB Meningitis (most common indication), TB Pericarditis (to prevent constrictive pericarditis), Pleural effusion (for rapid resolution), and Renal TB (to prevent strictures) [1]. * **Contraindications:** Intestinal TB (due to perforation risk) and Multi-Drug Resistant TB (MDR-TB) unless life-threatening inflammation is present. * **Standard Regimen:** Prednisolone (1-2 mg/kg) tapered over 4–8 weeks is the typical adjuvant protocol.

Question 633: Corticosteroids are absolutely contraindicated in which of the following types of tuberculosis?

A. Miliary
B. Meningeal
C. Intestinal (Correct Answer)
D. Renal

Explanation: **Explanation:** In the management of Tuberculosis (TB), corticosteroids are used as an adjuvant therapy to reduce the inflammatory response and prevent complications like fibrosis or excessive exudation. However, they are **absolutely contraindicated in Intestinal TB.** **Why Intestinal TB?** The primary concern in Intestinal TB is the risk of **bowel perforation**. Corticosteroids inhibit the healing process and mask signs of peritonitis. In the gut, TB typically causes ulcerations; steroids can lead to thinning of the intestinal wall, preventing the formation of protective adhesions and significantly increasing the risk of a life-threatening perforation. **Analysis of Other Options:** * **Meningeal TB (Option B):** This is a primary indication for steroids [1]. They reduce intracranial pressure, decrease cerebral edema, and prevent basal arachnoiditis, which significantly lowers mortality and neurological deficits [1]. * **Miliary TB (Option A):** Steroids are often used as an adjunct, especially if there is associated respiratory distress (ARDS) or adrenal insufficiency, to dampen the overwhelming systemic inflammatory response. * **Renal TB (Option D):** While not mandatory for all cases, steroids are used to prevent ureteric strictures and subsequent hydronephrosis during the healing phase of the disease. **High-Yield Clinical Pearls for NEET-PG:** * **Indications for Steroids in TB:** Meningitis (Grade I, II, III) [1], Pericarditis (to prevent constrictive pericarditis) [1], Pleural effusion (to hasten fluid absorption), and Laryngeal TB (to prevent airway obstruction). * **Standard Regimen:** Dexamethasone or Prednisolone is typically tapered over 6–8 weeks. * **Contraindication:** Always avoid steroids in TB if the patient has not started effective Anti-Tubercular Therapy (ATT), as it can lead to uncontrolled bacterial multiplication.

Question 634: According to RNTCP, tubercular pericarditis should be treated with which category of anti-tubercular regimen?

A. Category III
B. Category I (Correct Answer)
C. Category II
D. Category IV

Explanation: Under the **Revised National Tuberculosis Control Programme (RNTCP)**—now integrated into the National TB Elimination Programme (NTEP)—tuberculosis is categorized based on the site of infection and treatment history. **Why Category I is correct:** **Category I** is indicated for all **newly diagnosed** cases of tuberculosis, whether they are pulmonary or extra-pulmonary [1]. **Tubercular pericarditis** is classified as a **Seriously Ill Extra-Pulmonary TB (EP TB)** case. According to RNTCP guidelines, all new cases of EP TB (including pericardial, spinal, meningeal, and miliary TB) must be treated with Category I. This regimen consists of a 2-month Intensive Phase (HRZE) followed by a 4-month Continuation Phase (HRE) [1]. **Analysis of Incorrect Options:** * **Category III:** Historically used for "non-cavitary, smear-negative pulmonary TB" or "less serious EP TB." However, RNTCP phased out Category III years ago to simplify treatment; all new cases now fall under Category I. * **Category II:** Previously reserved for "previously treated" cases (relapse, failure, or treatment after default). Under the latest WHO and NTEP updates, the "Category II" retreatment regimen (which included Streptomycin) has been discontinued to prevent the amplification of drug resistance. * **Category IV:** This category is strictly reserved for **Multi-Drug Resistant TB (MDR-TB)** cases, not for drug-sensitive extra-pulmonary cases like standard TB pericarditis. **High-Yield Clinical Pearls for NEET-PG:** * **Steroid Adjunct:** In Tubercular Pericarditis, **Corticosteroids** (e.g., Prednisolone) are often added to the Category I regimen to reduce the risk of constrictive pericarditis and decrease mortality [2]. * **Treatment Duration:** While the standard duration is 6 months, for specific sites like TB Meningitis or Bone/Joint TB, the continuation phase may be extended based on clinical judgment [1]. * **Diagnosis:** The gold standard for TB pericarditis is the identification of *M. tuberculosis* in pericardial fluid or a pericardial biopsy (high ADA levels are a common supportive finding) [2].

Question 635: All of the following are indications for steroid use in Tuberculosis except?

A. Bone TB (Correct Answer)
B. Tubercular meningitis
C. Pericardial effusion
D. Massive pleural effusion

Explanation: The use of corticosteroids in Tuberculosis (TB) is based on the principle of reducing the detrimental host inflammatory response, which can cause tissue damage or mechanical obstruction. **Why Bone TB is the correct answer:** In **Bone and Joint TB** (including Pott’s spine), there is no evidence that steroids improve outcomes [1]. Management relies strictly on Anti-Tubercular Therapy (ATT) and, in specific cases, surgical intervention for stabilization or decompression [2]. Steroids do not prevent deformity or improve neurological recovery in these patients. **Analysis of Incorrect Options:** * **Tubercular Meningitis (TBM):** This is the most definitive indication. Steroids (Dexamethasone/Prednisolone) reduce cerebral edema, intracranial pressure, and vasculitis, significantly decreasing mortality and neurological deficits [1]. * **Pericardial Effusion:** Steroids reduce the risk of constrictive pericarditis and the need for repeated pericardiocentesis by decreasing fibrin deposition and pericardial thickening [1]. * **Massive Pleural Effusion:** While not mandatory for all pleural TB, steroids are indicated in **massive** effusions to hasten the resolution of fluid, prevent pleural thickening (fibrothorax), and alleviate severe respiratory distress. **High-Yield Clinical Pearls for NEET-PG:** 1. **Other Indications:** Adrenal TB (Addisonian crisis), Laryngeal TB (to prevent airway obstruction), and Miliary TB (if severe hypoxia/ARDS is present). 2. **IRIS:** Steroids are the treatment of choice for Paradoxical IRIS (Immune Reconstitution Inflammatory Syndrome) in HIV-TB co-infected patients. 3. **Rule of Thumb:** Steroids should **never** be given without concurrent ATT coverage to prevent uncontrolled mycobacterial replication.

Question 636: Significant bacteriuria is defined as the presence of which of the following number of bacteria per ml of urine?

A. 100-1000
B. 1000-10,000
C. 10,000-100,000
D. >100,000 (Correct Answer)

Explanation: The concept of **Significant Bacteriuria** was established by Edward Kass to distinguish true urinary tract infection (UTI) from contamination [1]. The standard definition is the presence of **≥10⁵ (100,000) colony-forming units (CFU) per ml** of urine in a clean-catch midstream sample. This threshold provides high specificity for identifying active bacterial multiplication in the bladder [1]. * **Option D (>100,000) is Correct:** This is the classical "Kass Criteria" used to diagnose asymptomatic bacteriuria and most symptomatic UTIs. It represents a high bacterial load unlikely to be caused by skin flora contamination during voiding. * **Options A, B, and C are Incorrect:** These values (100 to 100,000 CFU/ml) are generally considered "low-count bacteriuria." While they may represent early infection or contamination, they do not meet the traditional definition of significant bacteriuria for a standard midstream sample. **High-Yield Clinical Pearls for NEET-PG:** 1. **Exceptions to the 10⁵ Rule:** In symptomatic females with cystitis, a lower threshold of **≥10² CFU/ml** (coliforms) is often considered significant. 2. **Suprapubic Aspiration:** Any growth of bacteria (even 1 CFU/ml) from a suprapubic needle aspiration is considered significant. 3. **Catheterized Patients:** In patients with indwelling catheters, a threshold of **≥10² to 10³ CFU/ml** is typically used to define infection. 4. **Asymptomatic Bacteriuria:** Requires two consecutive voided specimens with ≥10⁵ CFU/ml in females, or a single specimen in males. Treatment is only indicated in **pregnant women** and patients undergoing **urological procedures**.

Question 637: A 17-year-old man presents with fatigue, malaise, fever, and sore throat. He has no significant past medical history and is not on any medications. Physical examination reveals enlarged, palpable cervical lymph nodes. He reports no weight loss or night sweats. Laboratory investigations include a normal chest x-ray, negative throat swab, and an abnormal blood film with atypical lymphocytes. His hemoglobin is 15.5 g/dL; hematocrit 42%; platelets 290,000/mL; WBC 10,500/mL, with 45% segmented neutrophils, 1% eosinophils, and 54% lymphocytes, of which 36% were atypical. Which of the following is the most appropriate initial diagnostic test?

A. Lymph node biopsy
B. Bone marrow examination
C. Erythrocyte sedimentation rate (ESR)
D. Heterophil antibody (Monospot) test (Correct Answer)

Explanation: ### Explanation The clinical presentation of fever, sore throat, cervical lymphadenopathy, and fatigue in a young adult is classic for **Infectious Mononucleosis (IM)**, most commonly caused by the **Epstein-Barr Virus (EBV)** [1]. **1. Why the Correct Answer is Right:** The presence of **atypical lymphocytes** (Downey cells) on the peripheral blood film is a hallmark of IM [1]. These are actually activated T-cells responding to B-cells infected by EBV. The **Heterophil antibody (Monospot) test** is the most appropriate initial diagnostic step. It detects IgM antibodies that agglutinate sheep or horse red blood cells. It is highly specific (approx. 94-99%) in the clinical context of IM and is the standard rapid screening test. **2. Why Incorrect Options are Wrong:** * **A. Lymph node biopsy:** This is an invasive procedure used to rule out malignancy (like Lymphoma) [2]. While the patient has lymphadenopathy, the presence of atypical lymphocytes and a sore throat strongly points toward a viral etiology rather than a primary nodal malignancy [2]. * **B. Bone marrow examination:** This is indicated for suspected hematologic malignancies or unexplained cytopenias. This patient has a normal hemoglobin, platelet count, and total WBC count, making leukemia unlikely [2]. * **C. Erythrocyte sedimentation rate (ESR):** ESR is a non-specific marker of inflammation [2]. While it may be elevated, it does not provide a definitive or specific diagnosis for the cause of the patient's symptoms. **3. NEET-PG High-Yield Pearls:** * **Triad of IM:** Fever, Pharyngitis, and Lymphadenopathy (usually posterior cervical). * **Hematology:** Absolute lymphocytosis (>50% of WBCs) with >10% atypical lymphocytes. * **Complication:** Splenomegaly occurs in 50% of cases; patients must avoid contact sports to prevent **splenic rupture**. * **Clinical Caution:** Administration of **Ampicillin or Amoxicillin** in a patient with IM often results in a characteristic maculopapular rash (not a true allergy). * **EBV-Specific Serology:** If the Monospot is negative but suspicion remains high, test for **Viral Capsid Antigen (VCA) IgM/IgG**.

Question 638: Which of the following is NOT a feature of cerebral malaria?

A. Focal neurologic deficit (Correct Answer)
B. Retinal hemorrhages
C. Extensor plantar reflex
D. Absent abdominal reflex

Explanation: **Explanation:** Cerebral malaria, caused by *Plasmodium falciparum*, is defined as a clinical syndrome characterized by coma (Glasgow Coma Scale <11 in adults) at least 1 hour after the termination of a seizure, in the presence of asexual malaria parasites on a blood film. **Why Focal Neurologic Deficit is the correct answer:** Cerebral malaria is typically a **diffuse encephalopathy**. While patients present with altered consciousness and generalized seizures, **focal neurological deficits** (such as hemiplegia or cranial nerve palsies) are **uncommon** and should prompt a search for alternative diagnoses like a brain abscess, stroke, or post-ictal state (Todd’s paralysis). **Analysis of other options:** * **Retinal Hemorrhages:** These are a classic and specific finding in cerebral malaria (malarial retinopathy). They are highly prognostic; their presence correlates with the severity of brain involvement and increased mortality. * **Extensor Plantar Reflex (Babinski Sign):** Upper motor neuron signs are common in cerebral malaria due to diffuse cortical dysfunction. An extensor plantar response is frequently observed during the comatose state. * **Absent Abdominal Reflex:** This is a common clinical finding in cerebral malaria, reflecting the involvement of the corticospinal tracts. **NEET-PG High-Yield Pearls:** * **Pathogenesis:** Sequestration of parasitized RBCs in cerebral microvasculature (cytoadherence) leading to hypoxia and cytokine release [1]. * **Drug of Choice:** Intravenous **Artesunate** is the gold standard (superior to Quinine). * **Poor Prognostic Markers:** Deep coma, retinal hemorrhages, metabolic acidosis (most important predictor of death), and hyperlactatemia. * **CSF Findings:** Usually normal or slightly elevated protein; pleocytosis is rare (helps differentiate from bacterial meningitis).

Question 639: What is the recommended prophylaxis for a pinprick injury in an HIV-positive individual, EXCEPT for which of the following?

A. Zidovudine for 4 weeks
B. If there is a scalpel cut wound, use Zidovudine with Stavudine and Lamivudine
C. Regular blood testing
D. Acyclovir for 12 months (Correct Answer)

Explanation: ### Explanation The question asks for the intervention that is **NOT** part of the standard Post-Exposure Prophylaxis (PEP) protocol for HIV. **Why Option D is Correct:** **Acyclovir** is an antiviral medication used to treat Herpes Simplex Virus (HSV) and Varicella-Zoster Virus (VZV). It has **no activity against HIV** (a retrovirus) because it requires viral thymidine kinase for activation, which HIV lacks. Furthermore, PEP for HIV is typically administered for **28 days (4 weeks)**, not 12 months. Therefore, Acyclovir has no role in HIV prophylaxis. **Analysis of Incorrect Options:** * **Option A:** **Zidovudine (AZT)** was the historical backbone of PEP. While modern guidelines (NACO/WHO) now prefer a three-drug regimen (typically Tenofovir + Lamivudine + Dolutegravir), Zidovudine for 4 weeks remains a classic textbook answer for HIV prophylaxis. * **Option B:** For high-risk exposures like a deep scalpel cut, a **multi-drug (expanded) regimen** is indicated. While the specific combination of Zidovudine + Stavudine is avoided today due to antagonism, the concept of using a 3-drug regimen for 4 weeks for significant injuries is correct. * **Option C:** **Regular blood testing** is mandatory. Baseline testing is done to rule out pre-existing infection, followed by repeat testing at 6 weeks, 3 months, and sometimes 6 months to monitor for seroconversion [1]. In the event of accidental needle-pricks or cuts with contaminated instruments, the wound should be immediately washed under running water and reported to authorities for appropriate testing and counseling [1]. **Clinical Pearls for NEET-PG:** * **Golden Period:** PEP should ideally be started within **2 hours**, and no later than **72 hours** post-exposure. * **Duration:** Always **28 days**. * **Current NACO Regimen:** TLE (Tenofovir 300mg + Lamivudine 300mg + Efavirenz 600mg) or TL + Dolutegravir (preferred). * **Risk of Transmission:** Percutaneous HIV exposure carries a roughly **0.3%** risk, whereas Hepatitis B (in HBeAg positive) carries a much higher risk (up to 30%).

Question 640: What is the drug of choice for the treatment of latent syphilis?

A. Penicillin (Correct Answer)
B. Erythromycin
C. Tetracycline
D. Ciprofloxacin

Explanation: Explanation: Penicillin G remains the gold standard and drug of choice for all stages of syphilis, including latent syphilis. The underlying medical concept is that Treponema pallidum is exquisitely sensitive to penicillin, and despite decades of use, no documented resistance has emerged. For latent syphilis, the goal is to prevent progression to tertiary syphilis and transmission. * Early Latent Syphilis (<1 year): Treated with a single IM dose of Benzathine Penicillin G (2.4 million units). * Late Latent Syphilis (>1 year or unknown duration): Treated with three weekly doses of Benzathine Penicillin G (7.2 million units total). Analysis of Incorrect Options: * B. Erythromycin: While once used, it is no longer recommended due to high rates of treatment failure and increasing resistance. It also does not reliably cross the placental barrier. * C. Tetracycline (or Doxycycline): These are considered second-line alternatives for non-pregnant, penicillin-allergic patients. However, they are less effective than penicillin and require longer courses (28 days for late latent). * D. Ciprofloxacin: Fluoroquinolones have no clinical role in the treatment of syphilis. High-Yield Clinical Pearls for NEET-PG: 1. Jarisch-Herxheimer Reaction: An acute febrile reaction occurring within 24 hours of starting penicillin; it is caused by the release of endotoxins from dying spirochetes. It is not an allergic reaction. 2. Pregnancy: Penicillin is the only acceptable treatment. If a pregnant woman is allergic, she must undergo desensitization followed by penicillin treatment. 3. Neurosyphilis: Requires Aqueous Crystalline Penicillin G (IV), as Benzathine penicillin does not achieve therapeutic levels in the CSF.

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

Practice Questions

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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