Infectious Diseases Practice Questions

Q: What is the percentage of coincidence between a sore throat and acute rheumatic fever?

3%. ### Explanation **1. Understanding the Correct Answer (Option A: 3%)** Acute Rheumatic Fever (ARF) is a nonsuppurative inflammatory complication that follows a Group A Streptococcal (GAS) pharyngitis. Epidemiological studies conducted in the mid-20th century (notably at Warren Air Force Base) established that approximately **3% of individuals** with untreated or inadequately treated exudative streptococcal sore throats will develop ARF. This "3% rule" applies specifically to epidemic situations [1]. In endemic settings or during sporadic outbreaks, the attack rate can be significantly lower (often <1.0%), but for standardized examinations like NEET-PG, 3% is the classic, high-yield figure. **2. Analysis of Incorrect Options** * **Option B (5%):** This overestimates the incidence. While GAS is common, the host immune response required to trigger ARF is specific and occurs in a minority of the population. * **Options C & D (7% and 9%):** These figures are significantly higher than documented clinical data. Even in the absence of antibiotics, the vast majority of patients with a sore throat do not develop the systemic autoimmune response characteristic of ARF. **3. Clinical Pearls for NEET-PG** * **The Latent Period:** ARF typically develops **1–5 weeks** (average 3 weeks) after the initial sore throat. * **Prevention:** Primary prevention of ARF involves treating GAS pharyngitis with a single dose of Benzathine Penicillin G or a 10-day course of oral Penicillin V [1]. * **Jones Criteria:** Diagnosis is clinical, based on the Revised Jones Criteria (Major: Carditis, Polyarthritis, Chorea, Erythema Marginatum, Subcutaneous nodules) [1]. * **Site Specificity:** Note that ARF follows **pharyngeal** infections only, whereas Post-Streptococcal Glomerulonephritis (PSGN) can follow either pharyngeal or skin (impetigo) infections.

Q: What is an alternative parenteral drug for multi-drug resistant malaria?

Artemisinin. **Explanation:** The treatment of multi-drug resistant (MDR) malaria, particularly *Plasmodium falciparum*, requires rapid-acting schizonticides to prevent progression to severe disease. **Correct Option: C. Artemisinin** Artemisinin and its derivatives (Artesunate, Artemether) are the drugs of choice for MDR malaria. They act by producing free radicals within the parasite's food vacuole, leading to rapid reduction in parasite biomass. While **Artesunate** is the preferred parenteral (IV/IM) agent globally due to its superior solubility and efficacy, **Artemisinin** serves as the parent compound and the correct alternative parenteral choice among the provided options for resistant cases. **Analysis of Incorrect Options:** * **A. Mefloquine:** This is an oral drug used for prophylaxis or as part of combination therapy. It is not available in a parenteral formulation and is associated with neuropsychiatric side effects. * **B. Sulfamethoxazole:** This is a sulfonamide used in combination with Pyrimethamine (Fansidar). It is an oral folate antagonist and is not used as a standalone parenteral treatment for MDR malaria. * **D. Dihydroartemisinin:** While a potent metabolite of artemisinin, it is primarily administered **orally** (often in combination with Piperaquine). It is not the standard parenteral alternative compared to Artemisinin/Artesunate. **NEET-PG High-Yield Pearls:** * **Drug of Choice for Severe/Cerebral Malaria:** Intravenous **Artesunate** (preferred over Quinine). * **Mechanism of Action:** Artemisinins act via **endoperoxide bridge** cleavage, catalyzed by intra-parasitic iron, leading to oxidative stress. * **Safe in Pregnancy:** Artesunate is now considered safe in the **first trimester** for severe malaria (WHO guidelines). * **Gameto-cytocidal activity:** Artemisinins are effective against all stages of the parasite, including gametocytes, reducing transmission.

Q: A 29-year-old male is suspected of having viral encephalitis. Which of the following is the most likely result from CSF analysis?

Raised protein, raised lymphocytes, normal glucose. ### Explanation The hallmark of viral infections of the Central Nervous System (CNS), including meningitis and encephalitis, is **lymphocytic pleocytosis** with relatively preserved biochemical parameters compared to bacterial infections [1]. **Why Option A is correct:** In viral encephalitis, the inflammatory response leads to an influx of white blood cells, predominantly **lymphocytes**. The inflammation also causes a breakdown of the blood-brain barrier, resulting in **mildly to moderately raised protein** levels. Crucially, viruses do not consume glucose for metabolism; therefore, the **CSF glucose remains normal** (typically >60% of blood glucose) [1]. **Why the other options are incorrect:** * **Option B:** Encephalitis typically triggers an immune response [2]; a "normal lymphocyte" count is rare unless the patient is severely immunocompromised or in the very early hyperacute phase. * **Option C & D:** **Raised glucose** in CSF is not a diagnostic feature of any CNS infection. High CSF glucose usually reflects systemic hyperglycemia (as CSF glucose levels follow blood glucose levels). --- ### High-Yield Clinical Pearls for NEET-PG: 1. **The "Rule of Two":** In viral CNS infections, look for **Normal Glucose** and **Lymphocytic Predominance**. 2. **Bacterial vs. Viral:** Bacterial meningitis shows **low glucose** (hypoglycorrhachia) and **neutrophilic** predominance. 3. **HSV Encephalitis:** If the question mentions **hemorrhagic** CSF or involvement of the **temporal lobes** on MRI, think Herpes Simplex Virus (HSV-1) [2]. This is the most common cause of sporadic fatal encephalitis. 4. **Xanthochromia:** If the CSF is yellowish, it indicates old blood (Subarachnoid Hemorrhage), not typical viral encephalitis. 5. **TB Meningitis:** Characterized by very high protein, very low glucose, and lymphocytic pleocytosis (often confused with viral, but glucose is the differentiator).

Q: What is the outpatient treatment for community-acquired pneumonia?

Azithromycin. The treatment of Community-Acquired Pneumonia (CAP) is guided by the likely causative organisms, most commonly *Streptococcus pneumoniae*, *Haemophilus influenzae*, and atypical pathogens like *Mycoplasma pneumoniae* [3]. **1. Why Azithromycin is correct:** In previously healthy outpatients with no risk factors for drug-resistant *S. pneumoniae*, **Macrolides** (Azithromycin or Clarithromycin) or **Doxycycline** are the first-line empirical treatments. Azithromycin is preferred due to its excellent coverage against atypical pathogens and its convenient once-daily dosing [3]. In regions with high macrolide resistance or for patients with comorbidities, a respiratory fluoroquinolone (e.g., Levofloxacin) or a combination of a Beta-lactam plus a Macrolide is indicated. **2. Why the other options are incorrect:** * **Cefotaxime:** This is a third-generation cephalosporin administered parenterally (IV/IM). It is used for inpatient management of CAP, not for routine outpatient treatment. * **Ampicillin:** While active against some gram-positive organisms, it is inactivated by beta-lactamase-producing strains of *H. influenzae* and has no activity against atypical pathogens, making it poor monotherapy for CAP [3]. * **Gentamicin:** This aminoglycoside is primarily active against aerobic gram-negative bacilli. It has poor lung penetration and no activity against *S. pneumoniae* or atypicals, making it inappropriate for CAP. **High-Yield Clinical Pearls for NEET-PG:** * **CURB-65 Score:** Used to decide the site of care (Outpatient vs. Inpatient) [2]. A score of 0-1 suggests outpatient treatment. * **Atypical Pneumonia:** Characterized by a subacute onset and "walking pneumonia" symptoms; Macrolides are the drug of choice [3]. * **Drug of Choice for MRSA Pneumonia:** Linezolid or Vancomycin [1]. * **Drug of Choice for *Legionella*:** Azithromycin or Levofloxacin.

Q: A 21-year-old medical student suffered a needle stick injury. The patient has a history of illicit intravenous drugs abuse. One month later, the medical student develops jaundice. Which of the following findings would implicate hepatitis B as the etiology?

Positive hepatitis B surface antigen. **Explanation:** The clinical presentation describes an acute onset of jaundice following a high-risk parenteral exposure (needle stick injury). To diagnose acute Hepatitis B Virus (HBV) infection, one must identify markers of active viral replication [1]. **Why Option A is Correct:** **Hepatitis B surface antigen (HBsAg)** is the first serological marker to appear in the blood after infection, often detectable 2 to 6 weeks before the onset of symptoms or jaundice [1]. Its presence indicates an active (acute or chronic) infection. In this scenario, one month post-exposure, HBsAg is the most reliable indicator that the student has contracted HBV [2]. **Why Other Options are Incorrect:** * **Option B (Anti-HBs):** This antibody indicates immunity, either from a successful vaccination or recovery from a past infection [2]. It does not signify an active, acute illness. * **Option C (Anti-HAV):** This indicates a past or present Hepatitis A infection [3]. HAV is transmitted via the fecal-oral route, not through needle stick injuries (parenteral). * **Option D (Anti-HBc):** While IgM anti-HBc is a marker of acute infection, "Anti-HBc" (Total) is non-specific as it remains positive for life after any natural infection [2]. Without specifying the IgM isotype, HBsAg is a more definitive marker for diagnosing the etiology of the current jaundice. **NEET-PG High-Yield Pearls:** 1. **Window Period:** The interval when HBsAg becomes negative but Anti-HBs has not yet appeared. During this time, **IgM Anti-HBc** is the only diagnostic marker of acute HBV [1]. 2. **HBeAg:** Indicates high viral replication and maximum infectivity. 3. **Post-Exposure Prophylaxis (PEP):** If a student is unvaccinated, PEP involves both the HBV vaccine and Hepatitis B Immune Globulin (HBIG), ideally within 24 hours.

Q: Cytomegalovirus (CMV) retinitis in HIV patients typically occurs when the CD4 count falls below which threshold?

100 cells/mm³. **Explanation:** **Correct Answer: B. 100 cells/mm³** Cytomegalovirus (CMV) is a double-stranded DNA virus (Beta-herpesvirus) that remains latent in myeloid progenitor cells. In HIV-infected individuals, CMV reactivation is a classic opportunistic infection that occurs during advanced stages of immunosuppression. While the risk significantly increases as the CD4 count drops, **100 cells/mm³** is the clinically established threshold below which CMV retinitis typically manifests. It is the most common cause of blindness in AIDS patients, characterized by "pizza-pie" or "cottage cheese and ketchup" fundoscopic appearances (hemorrhage with yellowish-white exudates). **Analysis of Incorrect Options:** * **A. 50 cells/mm³:** While CMV risk is highest and most severe below 50 cells/mm³ (often the threshold for disseminated CMV or CMV colitis), the initial clinical threshold for monitoring and onset of retinitis is 100 cells/mm³. * **C. 200 cells/mm³:** This is the threshold for defining AIDS and the primary cutoff for *Pneumocystis jirovecii* pneumonia (PCP) prophylaxis. CMV rarely occurs at this level. * **D. 150 cells/mm³:** This threshold is associated with an increased risk of fungal infections like *Histoplasma capsulatum* in endemic areas, but it is not the standard cutoff for CMV. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** Ganciclovir (or Valganciclovir). Foscarnet is used for ganciclovir-resistant strains. * **Histology:** "Owl’s eye" intranuclear inclusion bodies. * **Screening:** HIV patients with CD4 <100 cells/mm³ should undergo regular ophthalmologic screening every 3–6 months. * **Immune Reconstitution Inflammatory Syndrome (IRIS):** Starting HAART in a patient with CMV can lead to "Immune Recovery Uveitis."

Q: One day after a casual sexual encounter with a bisexual man recently diagnosed as antibody-positive for human immunodeficiency virus (HIV), a patient is concerned about whether she may have become infected. A negative antibody titer is obtained. To test for seroconversion, when is the earliest repeat antibody testing should be scheduled after the sexual encounter?

6 to 12 weeks. ### Explanation **Correct Option: C (6 to 12 weeks)** The primary concept here is the **"Window Period."** This is the interval between the initial HIV infection and the time when the body produces enough antibodies to be detected by standard screening tests (ELISA) [1]. While modern 4th-generation assays (which detect both p24 antigen and antibodies) can detect infection as early as 2–3 weeks, the traditional **antibody-only seroconversion** typically occurs within **6 to 12 weeks** in the vast majority of patients. By 3 months (12 weeks), more than 95% of individuals will have detectable antibodies [3]. Therefore, to reliably confirm or rule out seroconversion via antibody testing, the earliest recommended window starts at 6 weeks [3]. **Analysis of Incorrect Options:** * **A (1 to 2 weeks):** This is too early for an antibody response. Only HIV-RNA (viral load) via PCR might be detectable at this stage [2]. * **B (3 to 4 weeks):** While a 4th-generation p24 antigen test might be positive, an **antibody-only** titer (as specified in the question) is often still negative during this period. * **D (12 to 15 weeks):** While testing at this stage is highly accurate, it is not the *earliest* time to schedule a repeat test. 6 to 12 weeks is the standard diagnostic window [3]. **NEET-PG High-Yield Pearls:** 1. **Order of Detection:** Viral RNA (10–12 days) → p24 Antigen (14–16 days) → Antibodies (3–12 weeks). 2. **Screening Test:** ELISA (High sensitivity) [1]. 3. **Confirmatory Test:** Western Blot (detects antibodies to specific proteins like gp41, gp120, p24) [1]. *Note: Newer algorithms use HIV-1/2 differentiation assays.* 4. **Post-Exposure Prophylaxis (PEP):** Must be started within **72 hours** of exposure and continued for 28 days (Tenofovir + Emtricitabine + Dolutegravir/Raltegravir).

Q: What is the cornerstone treatment for dengue fever with warning signs, in the absence of shock or hemorrhage?

Intravenous fluids. The cornerstone of management for dengue fever with warning signs is **Intravenous (IV) fluid therapy**. The pathophysiology of severe dengue is characterized by increased capillary permeability leading to plasma leakage. This results in hemoconcentration and potential hypovolemic shock [1]. Administering isotonic crystalloids (like Normal Saline or Ringer’s Lactate) counteracts this leakage, maintains intravascular volume, and prevents progression to Dengue Shock Syndrome (DSS) [1]. **Analysis of Incorrect Options:** * **A. Platelet transfusion:** This is not indicated based on platelet count alone. It is reserved for patients with significant bleeding or very low counts (<10,000/mm³) with high risk of hemorrhage. Prophylactic transfusion does not improve outcomes. * **C. Cryoglobulins:** These have no role in the management of dengue. Cryoprecipitate may be used in rare cases of disseminated intravascular coagulation (DIC), but it is not a primary treatment. * **D. Antivirals:** There are currently no approved or effective antiviral drugs for the treatment of Dengue virus; management remains purely supportive. **High-Yield Clinical Pearls for NEET-PG:** * **Warning Signs:** Abdominal pain/tenderness, persistent vomiting, mucosal bleed, lethargy, liver enlargement >2cm, and a rapid increase in Hct with a rapid decrease in platelet count. * **Fluid Choice:** Isotonic crystalloids are the first choice. Colloids are reserved for refractory shock. * **Critical Period:** Usually occurs between days 3–7 of illness during the "defervescence" phase (when fever drops) [1]. This is when plasma leakage is most severe. * **Avoid:** NSAIDs (like Aspirin/Ibuprofen) due to the risk of bleeding; use Paracetamol for fever.

Question 1

What is the percentage of coincidence between a sore throat and acute rheumatic fever?

Accepted Answer

3%

Answer

5%

Answer

7%

Answer

9%

Question 2

What is an alternative parenteral drug for multi-drug resistant malaria?

Accepted Answer

Artemisinin

Answer

Mefloquine

Answer

Sulfamethoxazole

Answer

Dihydroartemisinin

Question 3

A 29-year-old male is suspected of having viral encephalitis. Which of the following is the most likely result from CSF analysis?

Accepted Answer

Raised protein, raised lymphocytes, normal glucose

Answer

Raised protein, normal lymphocytes, normal glucose

Answer

Raised protein, raised lymphocytes, raised glucose

Answer

Normal protein, raised lymphocytes, raised glucose

Question 4

What are the investigations in a clinically suspected case of tuberculosis?

Accepted Answer

Mantoux test (in children)

Answer

Sputum AFB

Answer

QuantiFERON TB Gold

Answer

Bactec

Question 5

What is the outpatient treatment for community-acquired pneumonia?

Accepted Answer

Azithromycin

Answer

Cefotaxime

Answer

Ampicillin

Answer

Gentamicin

Question 6

Post-transplant cytomegalovirus infection may cause which of the following?

Accepted Answer

Gastrointestinal ulceration and hemorrhage

Answer

Pyelonephritis

Answer

Cholecystitis

Answer

Intraabdominal abscess

Question 7

A 21-year-old medical student suffered a needle stick injury. The patient has a history of illicit intravenous drugs abuse. One month later, the medical student develops jaundice. Which of the following findings would implicate hepatitis B as the etiology?

Accepted Answer

Positive hepatitis B surface antigen

Answer

Positive antihepatitis B surface antibody

Answer

Positive antihepatitis A antibody

Answer

Positive antihepatitis B-core antibody

Question 8

Cytomegalovirus (CMV) retinitis in HIV patients typically occurs when the CD4 count falls below which threshold?

Accepted Answer

100 cells/mm³

Answer

50 cells/mm³

Answer

200 cells/mm³

Answer

150 cells/mm³

Question 9

One day after a casual sexual encounter with a bisexual man recently diagnosed as antibody-positive for human immunodeficiency virus (HIV), a patient is concerned about whether she may have become infected. A negative antibody titer is obtained. To test for seroconversion, when is the earliest repeat antibody testing should be scheduled after the sexual encounter?

Accepted Answer

6 to 12 weeks

Answer

1 to 2 weeks

Answer

3 to 4 weeks

Answer

12 to 15 weeks

Question 10

What is the cornerstone treatment for dengue fever with warning signs, in the absence of shock or hemorrhage?

Accepted Answer

Intravenous fluids

Answer

Platelet transfusion

Answer

Cryoglobulins

Answer

Antivirals

Infectious Diseases — MCQs

Infectious Diseases — MCQs

On this page

Practice by Chapter

Want unlimited practice?