Infectious Diseases Practice Questions

Q: A 65-year-old man presents with fever, severe headache, and nuchal rigidity. Physical examination shows a Glasgow coma score of 7. Lumbar puncture reveals cloudy cerebrospinal fluid (CSF) with 1200 neutrophils/mm3, elevated protein, and decreased glucose. Which of the following is the most probable etiologic agent of this condition?

Streptococcus pneumoniae. **Explanation:** The clinical presentation of fever, headache, and nuchal rigidity (meningismus) combined with a GCS of 7 indicates **Acute Bacterial Meningitis**. [1] **1. Why Streptococcus pneumoniae is correct:** The CSF analysis is the diagnostic gold standard. A "cloudy" appearance with a high neutrophil count (>1000/mm³), elevated protein, and low glucose is classic for bacterial etiology. In adults over 20 years of age, **Streptococcus pneumoniae** is the most common cause of community-acquired bacterial meningitis. The severe presentation (GCS 7) is also characteristic, as pneumococcal meningitis often carries a higher morbidity and mortality rate compared to other pathogens. [1] **2. Why the other options are incorrect:** * **Arbovirus & Herpesvirus:** These cause viral meningitis/encephalitis. CSF typically shows **lymphocytic pleocytosis**, normal glucose levels, and clear fluid. [1] While HSV-1 can cause severe encephalitis, the CSF profile here (1200 neutrophils, low glucose) is purely bacterial. * **Mycobacterium tuberculosis:** Tuberculous meningitis usually presents subacutely. [2] CSF analysis typically shows a **lymphocytic predominance** (not neutrophils) and a characteristically very high protein level with moderately low glucose. [2] **3. NEET-PG High-Yield Pearls:** * **Most common cause overall (Adults):** *S. pneumoniae*. * **Most common cause (Adolescents/Young Adults):** *Neisseria meningitidis* (look for petechial rashes). * **Empiric Treatment:** Ceftriaxone + Vancomycin. Add **Ampicillin** if *Listeria* is suspected (elderly or immunocompromised). [1] * **Steroids:** Dexamethasone should be given **before or with** the first dose of antibiotics to reduce neurological complications (especially in pneumococcal meningitis). * **CSF Glucose:** A CSF-to-serum glucose ratio of **<0.4** is highly suggestive of bacterial meningitis.

Q: What is the primary purpose of using combination therapy with anti-tubercular drugs?

To decrease the likelihood of developing drug resistance.. The primary rationale for combination therapy in Tuberculosis (TB) is the **prevention of drug resistance** [2]. *Mycobacterium tuberculosis* has a high rate of spontaneous genetic mutations. In any large bacterial population (such as in a cavitary lesion), a small fraction of bacilli will naturally possess resistance to a single drug (e.g., 1 in $10^6$ for Isoniazid). If monotherapy is used, these resistant mutants survive and multiply, leading to "acquired resistance." By using multiple drugs with different mechanisms of action simultaneously, the probability of a bacterium being resistant to all drugs at once becomes mathematically negligible (e.g., $10^{-6} imes 10^{-8} = 10^{-14}$), effectively sterilizing the lesion [3]. **Analysis of Incorrect Options:** * **Option A:** Combination therapy does not allow for a reduction in the standard therapeutic dose of individual drugs. Each drug must be administered at its full, effective dose to ensure bactericidal or bacteriostatic activity [1]. * **Option B:** Using multiple drugs actually **increases** the risk of adverse effects (e.g., combined hepatotoxicity from Isoniazid, Rifampicin, and Pyrazinamide) rather than minimizing them [1]. * **Option D:** Since A and B are incorrect, "All of the above" is invalid. **High-Yield Clinical Pearls for NEET-PG:** * **Bactericidal Drugs:** Isoniazid (INH), Rifampicin (RIF), Pyrazinamide (PZA), and Streptomycin. * **Bacteriostatic Drug:** Ethambutol (primarily used to prevent resistance to RIF if INH resistance exists). * **Sterilizing Action:** Rifampicin and Pyrazinamide are the most effective at killing semi-dormant bacilli, which reduces the risk of relapse. * **DOTS (Directly Observed Treatment Short-course):** The strategy used to ensure compliance and further prevent the emergence of Multi-Drug Resistant TB (MDR-TB) [2].

Q: What is the most common late central nervous system complication of HIV infection?

Dementia. **Explanation:** **HIV-Associated Dementia (HAD)**, also known as AIDS Dementia Complex, is the most common late-stage CNS complication of HIV infection [3]. It typically occurs when CD4 counts drop below **200 cells/mm³**. The underlying pathophysiology involves the direct infection of brain macrophages and microglia by HIV, leading to a chronic inflammatory state and neuronal damage, primarily affecting the subcortical structures. Clinically, it presents as a triad of cognitive decline, behavioral changes, and motor dysfunction. **Analysis of Options:** * **A. Dementia (Correct):** It is the hallmark late neurocognitive complication [1]. With the advent of HAART, the incidence has decreased, but it remains the most frequent primary CNS manifestation in advanced AIDS. * **B. Ataxia:** While ataxia can occur as part of the motor symptoms of HAD or due to opportunistic infections like Progressive Multifocal Leukoencephalopathy (PML), it is a focal sign rather than the most common overall complication. * **C. Seizures:** These are usually secondary to space-occupying lesions (e.g., CNS Toxoplasmosis or Primary CNS Lymphoma) [2] rather than a primary effect of the virus itself. * **D. Delirium:** This is an acute, reversible state of confusion often caused by systemic infections, metabolic derangements, or drug side effects, rather than a chronic late-stage complication of the virus. **Clinical Pearls for NEET-PG:** * **Most common opportunistic infection of CNS in HIV:** Toxoplasmosis [2]. * **Most common fungal infection of CNS in HIV:** Cryptococcal Meningitis. * **Most common cause of a space-occupying lesion in HIV:** Toxoplasmosis (Ring-enhancing lesions) [2]. * **Key distinction:** HAD is a **subcortical dementia** (characterized by psychomotor slowing), unlike Alzheimer’s, which is a cortical dementia.

Q: What is the drug of choice for treating Leptospirosis?

Penicillin. Leptospirosis is a zoonotic infection caused by the spirochete Leptospira interrogans. The choice of treatment depends on the severity of the clinical presentation [1]. 1. Why Penicillin is the Correct Answer: For severe or hospitalized cases of Leptospirosis (including Weil’s disease), Intravenous Penicillin G is traditionally considered the drug of choice. It effectively clears the spirochetemia and reduces the duration of fever and organ dysfunction. If the patient is allergic to penicillin, IV Ceftriaxone is a preferred alternative. 2. Analysis of Incorrect Options: * B. Tetracycline (Doxycycline): While Doxycycline is the drug of choice for mild/outpatient leptospirosis and is used for prophylaxis, Penicillin remains the standard answer for "drug of choice" in a general context or severe cases in medical examinations. * C. Sulfonamide: These are ineffective against spirochetes and have no role in the treatment of Leptospirosis. * D. Erythromycin: This is a second-line alternative used primarily in pregnant women who are allergic to Penicillin, but it is less effective than first-line agents. High-Yield Clinical Pearls for NEET-PG: * Jarisch-Herxheimer Reaction: Be alert for this reaction (fever, chills, hypotension) shortly after starting Penicillin due to the release of endotoxins from dying spirochetes. * Prophylaxis: Oral Doxycycline (200 mg once weekly) is used for individuals with high-risk exposure (e.g., floods, sewage workers). * Weil’s Disease Triad: Characterized by Jaundice, Renal failure (azotemia), and Hemorrhage (often pulmonary) [1]. * Gold Standard Diagnosis: Microscopic Agglutination Test (MAT) [1].

Q: Which of the following drugs are useful in the treatment of chronic Hepatitis B infection?

Lamivudine and Alpha interferon only. ### Explanation The treatment of **Chronic Hepatitis B (CHB)** focuses on suppressing viral replication to prevent the progression of cirrhosis and hepatocellular carcinoma. **1. Why Option A is Correct:** * **Lamivudine:** A nucleoside analogue that inhibits the HBV reverse transcriptase. While newer agents like Tenofovir and Entecavir are now preferred due to lower resistance rates, Lamivudine remains a classic, FDA-approved treatment for CHB. * **Alpha Interferon (IFN-α):** An immunomodulator that enhances the host immune response and has direct antiviral properties [1]. It is administered as a finite course (usually 48 weeks) and is particularly useful in patients with favorable genotypes and high ALT levels [1]. **2. Why Other Options are Incorrect:** * **Ribavirin (Options B, C, & D):** This is a cornerstone for treating **Hepatitis C (HCV)** (in combination with Interferon or DAAs) but has **no clinical efficacy** against Hepatitis B. * **Acyclovir (Option D):** This is an anti-herpetic medication used for HSV and VZV [2]. It does not inhibit the HBV polymerase effectively and is not used in the management of Hepatitis B [2]. **3. High-Yield Clinical Pearls for NEET-PG:** * **First-line Agents (Current Guidelines):** Tenofovir (TDF/TAF) and Entecavir are the preferred oral antivirals due to their high barrier to resistance. * **Interferon Contraindications:** Avoid in decompensated cirrhosis, pregnancy, and severe psychiatric illness [1]. * **HBeAg Seroconversion:** The primary goal of finite therapy (like IFN) is the loss of HBeAg and the development of anti-HBe [1]. * **HBV DNA:** The most sensitive marker for monitoring treatment response [1].

Q: The most sensitive among the following tests for the diagnosis of malaria is?

Quantitative buffy coat test. The diagnosis of malaria relies on the detection of Plasmodium parasites or their components in the blood. The **Quantitative Buffy Coat (QBC)** test is the most sensitive method among the options provided. [1] **1. Why QBC is the correct answer:** The QBC technique involves staining a specialized capillary tube with acridine orange and centrifuging it. [1] Centrifugation concentrates the parasites (which contain DNA) into a small area just below the white blood cell layer (the buffy coat). Because the parasites are **concentrated** and fluoresce under a microscope, QBC can detect as few as **5 parasites per microliter** of blood, making it significantly more sensitive than standard microscopy. **2. Why other options are incorrect:** * **Thin peripheral blood smear:** While excellent for **speciation** (identifying the species) and quantifying parasite density, it is less sensitive than thick smears or QBC because it uses a smaller volume of blood. * **PfHRP2 (Rapid Diagnostic Test):** This detects the Histidine-Rich Protein 2 of *P. falciparum*. While fast, it can yield false negatives in low parasitemia or "prozone effect" scenarios and false positives due to persistent antigens after treatment. [1] * **Pan plasmodial LDH:** This enzyme-based RDT is less sensitive than QBC and HRP2, particularly at low parasite levels, and is primarily used to monitor treatment response as LDH is only produced by live parasites. [1] **Clinical Pearls for NEET-PG:** * **Gold Standard:** Light microscopy (Thick and Thin smears) remains the "Gold Standard" for routine diagnosis. * **Thick Smear:** Used for **screening** (more sensitive than thin smear). * **Thin Smear:** Used for **species identification**. * **Most Sensitive Overall:** PCR (Polymerase Chain Reaction) is the most sensitive test available, but among the clinical/microscopic options listed, QBC is superior. [1] [2]

Q: CSF examination of a patient shows high protein, markedly low sugar, low chloride, and increased neutrophils. What is the most likely diagnosis?

Meningococcal meningitis. The CSF findings described—**high protein, markedly low sugar, and increased neutrophils**—are the classic biochemical signature of **Acute Bacterial Meningitis**. [1] ### 1. Why Meningococcal Meningitis is Correct Meningococcal meningitis (caused by *Neisseria meningitidis*) is a form of pyogenic bacterial meningitis. * **Increased Neutrophils (Polymorphonuclear Leucocytosis):** Bacteria trigger a massive recruitment of neutrophils to the subarachnoid space. * **Markedly Low Sugar (Hypoglycorrhachia):** Bacteria and active WBCs consume glucose; additionally, glucose transport into the CSF is impaired. * **High Protein:** Increased permeability of the blood-brain barrier and the presence of bacterial debris/inflammatory exudate raise protein levels. [1] * **Low Chloride:** Often seen in systemic infections and severe meningeal inflammation. ### 2. Why Other Options are Incorrect * **Viral Meningitis:** Typically presents with **lymphocytic** pleocytosis, **normal sugar**, and only mildly elevated protein. [1] * **Tuberculous Meningitis (TBM):** While it features high protein and low sugar, the predominant cells are **lymphocytes**, not neutrophils. TBM also typically has the lowest chloride levels among all types. * **Fungal Meningitis:** Similar to TBM, it presents with a **lymphocytic** picture and low sugar (though often not as low as bacterial). ### 3. NEET-PG Clinical Pearls * **Normal CSF Glucose:** 40–70 mg/dL (or >60% of blood glucose). * **Normal CSF Protein:** 15–45 mg/dL. * **The "Cobweb Coagulum":** Classically associated with Tuberculous Meningitis if the CSF is left standing. * **Drug of Choice:** For Meningococcal meningitis, **IV Ceftriaxone** is the mainstay. Prophylaxis for close contacts is **Rifampicin** (or Ciprofloxacin/Ceftriaxone).

Question 1

A 65-year-old man presents with fever, severe headache, and nuchal rigidity. Physical examination shows a Glasgow coma score of 7. Lumbar puncture reveals cloudy cerebrospinal fluid (CSF) with 1200 neutrophils/mm3, elevated protein, and decreased glucose. Which of the following is the most probable etiologic agent of this condition?

Accepted Answer

Streptococcus pneumoniae

Answer

Arbovirus

Answer

Herpesvirus

Answer

Mycobacterium tuberculosis

Question 2

What is the primary purpose of using combination therapy with anti-tubercular drugs?

Accepted Answer

To decrease the likelihood of developing drug resistance.

Answer

To decrease the required dosages of individual drugs.

Answer

To minimize the occurrence of adverse effects from the drugs.

Answer

All of the above.

Question 3

What is the most common late central nervous system complication of HIV infection?

Accepted Answer

Dementia

Answer

Ataxia

Answer

Seizures

Answer

Delirium

Question 4

What is the drug of choice for treating Leptospirosis?

Accepted Answer

Penicillin

Answer

Tetracycline

Answer

Sulfonamide

Answer

Erythromycin

Question 5

A 16-year-old female presents with a one-week history of small ulcers on her cheek and tongue, accompanied by a mild fever. Oral examination reveals multiple ulcers on the buccal and labial mucosa. She reports that her board examinations are in one week. What is the most appropriate management for this patient?

Accepted Answer

Symptomatic treatment, topical steroids, and relaxation techniques

Answer

Antibiotics and analgesics

Answer

Anti-fungal medications

Answer

Systemic steroids

Question 6

Which of the following drugs are useful in the treatment of chronic Hepatitis B infection?

Accepted Answer

Lamivudine and Alpha interferon only

Answer

Lamivudine and Ribavirin only

Answer

Alpha interferon and Ribavirin only

Answer

Lamivudine, Alpha interferon, Ribavirin, and Acyclovir

Question 7

A 23-year-old patient, studying abroad, visited his hometown and developed a high-grade fever (103°F) after 3 days. He took acetaminophen and subsequently complained of myalgias, cough, and mild shortness of breath. A nasopharyngeal swab tested positive for COVID-19. Which of the following statements regarding the patient's next steps in management is false?

Accepted Answer

HCQ + Azithromycin

Answer

Start Doxycycline 100mg

Answer

Start Ivermectin 12mg

Answer

Dexamethasone is used

Question 8

The most sensitive among the following tests for the diagnosis of malaria is?

Accepted Answer

Quantitative buffy coat test

Answer

Thin peripheral blood smear

Answer

PfHRP2 antigen test

Answer

Pan plasmodial LDH test

Question 9

In which of the following conditions are immunoglobulins indicated for a viral infection?

Accepted Answer

Severe Combined Immunodeficiency (SCID)

Answer

Human Immunodeficiency Virus (HIV)

Answer

Dengue fever

Answer

Severe malnutrition

Question 10

CSF examination of a patient shows high protein, markedly low sugar, low chloride, and increased neutrophils. What is the most likely diagnosis?

Accepted Answer

Meningococcal meningitis

Answer

Viral meningitis

Answer

Tuberculous meningitis

Answer

Fungal meningitis

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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