Infectious Diseases Practice Questions

Q: What is the most common opportunistic infection in patients with AIDS?

Candidiasis. **Explanation:** **Candidiasis (Option C)** is the correct answer because it is the most common opportunistic infection (OI) overall in patients with HIV/AIDS [1]. Specifically, **Oropharyngeal Candidiasis (Oral Thrush)** is the most frequent initial opportunistic fungal infection, often occurring when CD4 counts drop below 200-500 cells/mm³ [1]. While Esophageal Candidiasis is an AIDS-defining illness, the mucosal (oral) form remains the most prevalent clinical manifestation across the spectrum of the disease [2]. **Analysis of Incorrect Options:** * **Tuberculosis (Option B):** While TB is the most common **cause of death** in AIDS patients globally and the most common OI in the **Indian subcontinent**, it is not the most common infection overall worldwide. * **Cryptococcosis (Option A):** This is the most common **fungal meningitis** in AIDS patients (typically seen when CD4 <100 cells/mm³), but its incidence is lower than Candidiasis. * **Aspergillosis (Option D):** This is relatively uncommon in AIDS patients compared to other OIs; it usually occurs only in the setting of profound neutropenia or very advanced immunosuppression. **High-Yield Clinical Pearls for NEET-PG:** * **Most common OI overall:** Candidiasis [1]. * **Most common OI in India:** Tuberculosis. * **Most common life-threatening OI (USA/Global):** *Pneumocystis jirovecii* pneumonia (PCP) [1]. * **Most common CNS mass lesion:** Toxoplasmosis. * **Most common cause of blindness:** CMV Retinitis (CD4 <50 cells/mm³). * **Oral Thrush vs. Leukoplakia:** Unlike Oral Hairy Leukoplakia (caused by EBV), Candidial plaques **can** be scraped off, leaving an erythematous base.

Q: What is the treatment of choice for Pneumocystis jirovecii pneumonia?

Trimethoprim/sulfamethoxazole. **Explanation:** **Pneumocystis jirovecii pneumonia (PCP)** is a life-threatening opportunistic fungal infection primarily seen in immunocompromised patients, particularly those with HIV/AIDS (typically when CD4 counts fall below 200 cells/mm³). **1. Why Trimethoprim/sulfamethoxazole (TMP-SMX) is the Correct Choice:** TMP-SMX (Co-trimoxazole) is the **first-line treatment and prophylaxis** for PCP [1]. It works by inhibiting two consecutive steps in the fungal folic acid synthesis pathway. For moderate-to-severe infections, it is administered intravenously; for mild cases, oral administration is sufficient. In patients with severe hypoxia (PaO₂ 35 mmHg), **adjunctive corticosteroids** must be added to reduce the inflammatory response triggered by dying organisms [1]. **2. Why Other Options are Incorrect:** * **B. Erythromycin:** A macrolide antibiotic used for atypical pneumonias (like *Legionella* or *Mycoplasma*). It has no activity against *P. jirovecii*. * **C. Ofloxacin:** A fluoroquinolone used for bacterial infections (UTIs, respiratory infections). It is ineffective against fungal pathogens. * **D. Tetracycline:** Primarily used for Rickettsial infections or *Chlamydia*. It does not cover *P. jirovecii*. **High-Yield Clinical Pearls for NEET-PG:** * **Radiology:** Classic "bat-wing" appearance or bilateral perihilar ground-glass opacities on CXR/HRCT [1]. * **Diagnosis:** Definitive diagnosis requires visualization of cysts via **Gomori Methenamine Silver (GMS)** stain or Giemsa stain from induced sputum or Bronchoalveolar Lavage (BAL) [1]. * **Alternative Treatment:** If the patient is allergic to sulfa drugs, the second-line treatment is **Primaquine plus Clindamycin** or **Pentamidine**. * **Marker:** Elevated **Serum Beta-D-Glucan** is a highly sensitive (though non-specific) marker for PCP.

Q: Opisthotonus is typically seen in which of the following conditions?

Tetanus. **Explanation:** **Opisthotonus** is a state of severe hyperextension and spasticity in which an individual's head, neck, and spinal column enter into a complete "bridging" or arching position. **1. Why Tetanus is Correct:** Tetanus is caused by the toxin **tetanospasmin** produced by *Clostridium tetani* [2]. This toxin travels retrograde to the CNS and inhibits the release of inhibitory neurotransmitters (**GABA and Glycine**) from Renshaw cells. The loss of inhibition leads to unchecked muscular spasms. Opisthotonus occurs because the extensor muscles of the back are more powerful than the flexors, causing the characteristic backward arching during a generalized spasm. **2. Why Other Options are Incorrect:** * **Anthrax:** Caused by *Bacillus anthracis*, it typically presents as cutaneous eschars, hemorrhagic mediastinitis (inhalation), or GI distress, but does not cause generalized muscle arching. * **Tetany:** Caused by hypocalcemia, it presents with carpopedal spasm (Trousseau’s sign) and facial twitching (Chvostek’s sign), but not the full-body opisthotonic posturing seen in tetanus [3]. * **Rabies:** Characterized by hydrophobia, aerophobia, and localized spasms of the pharyngeal muscles (furious rabies) or ascending paralysis (dumb rabies), but not classic opisthotonus. **Clinical Pearls for NEET-PG:** * **Risus Sardonicus:** The "sardonic smile" caused by spasms of the facial muscles. * **Trismus (Lockjaw):** Usually the first clinical sign of tetanus. * **Management:** Neutralize unbound toxin with **Human Tetanus Immune Globulin (HTIG)** and use **Metronidazole** (preferred over Penicillin G as Penicillin is a GABA antagonist). * **Differential:** Opisthotonus can also be seen in **strychnine poisoning** [1], **phenothiazine toxicity** (extrapyramidal side effects), and **kernicterus**.

Q: Dengue fever is characterized by all except?

Increased clotting time. Dengue fever, caused by the Flavivirus and transmitted by the Aedes aegypti mosquito, is characterized by a triad of high-grade fever, severe body aches, and hematological changes. In Dengue, the coagulation profile typically shows a prolonged Prothrombin Time (PT) and Activated Partial Thromboplastin Time (aPTT) due to hepatic dysfunction and consumption of clotting factors. However, Clotting Time (CT)—which measures the intrinsic pathway—is generally not a diagnostic hallmark or a consistent finding in Dengue. Bleeding manifestations in Dengue are primarily driven by thrombocytopenia and vascular leakage rather than a primary defect in the clotting time. * Fever: Characteristically "saddle-back" (biphasic) and high-grade [1]. It is the most common presenting symptom. * Rash: Typically appears as a "white islands in a sea of red" (maculopapular) rash during the recovery phase [1]. * Thrombocytopenia: A hallmark of Dengue (especially DHF). It results from bone marrow suppression and immune-mediated destruction of platelets. * Vector: Aedes aegypti (Day biter, breeds in clean stagnant water). * Tourniquet Test: Positive if >10-20 petechiae per square inch; used as a screening tool for capillary fragility [1]. * Gold Standard Diagnosis: PCR (Days 1-5) or NS1 Antigen (Days 1-7). IgM ELISA is used after day 5. * Critical Phase: Occurs during defervescence (when fever drops); this is when plasma leakage and shock (Dengue Shock Syndrome) are most likely to occur [1]. * Lab Findings: Leukopenia (common early finding), increased hematocrit (indicates plasma leakage), and elevated AST/ALT.

Q: Which of the following medications used to treat severe cerebral malaria can cause hypoglycemia?

Quinine. Explanation: 1. Why Quinine is Correct: Quinine is a potent stimulator of the pancreatic beta cells, leading to the hypersecretion of insulin (hyperinsulinemia). This often results in profound hypoglycemia, which is a common and serious side effect, especially in pregnant patients and those with severe malaria [1]. In the context of cerebral malaria, this is particularly dangerous as hypoglycemia can mimic or worsen the neurological symptoms of the disease (e.g., altered consciousness, seizures). 2. Why the Other Options are Incorrect: * Chloroquine: While it can occasionally cause gastrointestinal upset or pruritus, it does not stimulate insulin release [1]. Its primary toxicity concerns are cardiovascular (arrhythmias) and retinal (with chronic use). * Halofantrine: The major concern with Halofantrine is cardiotoxicity, specifically QT interval prolongation, which can lead to fatal arrhythmias. It does not affect blood glucose levels. * Mefloquine: This drug is primarily associated with neuropsychiatric side effects, such as vivid dreams, anxiety, psychosis, and dizziness. It is not linked to hypoglycemia. High-Yield Clinical Pearls for NEET-PG: * The "Double Whammy": In severe malaria, hypoglycemia can be caused by both the parasite (consuming host glucose) and the treatment (Quinine-induced insulin release) [1]. * Monitoring: Always monitor blood glucose levels frequently in patients receiving IV Quinine [1]. * Drug of Choice: While Quinine was the traditional choice, Artesunate is now the preferred first-line treatment for severe malaria due to its superior efficacy and better safety profile (less hypoglycemia). * Cinchonism: Remember the classic triad of Quinine toxicity: Tinnitus, headache, and nausea.

Q: Hepatitis B infection is most commonly associated with which of the following conditions?

Serum sickness. The correct answer is **Serum sickness (Option C)**. This refers to the **prodromal, pre-icteric phase** of acute Hepatitis B virus (HBV) infection [1]. **Why Serum Sickness is Correct:** In the early stages of HBV infection, there is an excess of circulating Hepatitis B surface antigen (HBsAg) [1]. This leads to the formation of **Type III hypersensitivity immune complexes** (antigen-antibody complexes) that deposit in small vessels and joints. This manifests as a "serum sickness-like syndrome," characterized by the triad of **fever, skin rash (usually urticarial), and polyarthritis/arthralgia**. It typically resolves once jaundice appears [1]. **Analysis of Incorrect Options:** * **A. Polyarteritis nodosa (PAN):** While PAN is famously associated with HBV (10–30% of PAN cases are HBV-positive), it is a **late complication** or a chronic extrahepatic manifestation. In the context of "most common" early association or general prodromal presentation, serum sickness-like syndrome occurs more frequently during the acute phase. * **B. Systemic lupus erythematosus (SLE):** SLE is an autoimmune connective tissue disease with no direct causal link to HBV. In fact, chronic viral infections are sometimes studied as triggers for autoimmunity, but HBV is not a primary association for SLE. * **C. Polymyositis:** This is an inflammatory myopathy. While viral triggers are hypothesized, there is no established clinical association between HBV and polymyositis. **NEET-PG High-Yield Pearls:** * **Extrahepatic manifestations of HBV:** Serum sickness (most common prodrome), Polyarteritis Nodosa (PAN), and Membranous Glomerulonephritis (MGN). * **Hepatitis C associations:** Essential Mixed Cryoglobulinemia, Membranoproliferative Glomerulonephritis (MPGN), Porphyria Cutanea Tarda, and Lichen Planus. * **The "Gianotti-Crosti syndrome"** is a specific papular acrodermatitis of childhood associated with HBV.

Q: Primary atypical pneumonia is caused by all of the following organisms, EXCEPT:

Mumps virus. **Explanation:** Primary atypical pneumonia refers to a pulmonary infection where the clinical presentation differs from typical lobar pneumonia (e.g., *S. pneumoniae*). It is characterized by an insidious onset, non-productive cough, constitutional symptoms (headache, malaise), and a chest X-ray that shows diffuse interstitial infiltrates, often appearing "worse" than the patient's clinical state suggests. **Why Mumps virus is the correct answer:** While many viruses cause respiratory infections, the **Mumps virus** primarily targets the parotid glands and lymphoid tissue. It is **not** a recognized cause of primary atypical pneumonia. Its classic complications include orchitis, oophoritis, meningitis, and pancreatitis, but not interstitial lung disease. **Analysis of incorrect options:** * **Coxiella burnetii:** This is the causative agent of **Q fever**. It is a well-known cause of atypical pneumonia, often associated with exposure to livestock (cattle, sheep, goats). * **Influenza:** Influenza viruses (A and B) are common causes of viral atypical pneumonia, especially during seasonal outbreaks [1]. They can cause direct viral pneumonitis or predispose patients to secondary bacterial infections [1]. * **Measles:** The Measles virus can cause severe interstitial pneumonia (Hecht’s giant cell pneumonia), particularly in immunocompromised individuals or malnourished children. **NEET-PG High-Yield Pearls:** 1. **Most common cause:** *Mycoplasma pneumoniae* is the #1 cause of atypical pneumonia (associated with cold agglutinins and bullous myringitis). 2. **Legionella:** Often associated with hyponatremia, diarrhea, and exposure to contaminated water/AC systems [1]. 3. **Psittacosis (*C. psittaci*):** Look for a history of contact with birds/parrots and Horder’s spots. 4. **Radiology:** Atypical pneumonias typically show "reticulonodular" or "interstitial" patterns rather than consolidation.

Question 1

Which infectious disease among the following most closely resembles vasculitis?

Accepted Answer

Lyme disease

Answer

Rubella

Answer

Tuberculosis

Answer

Leprosy

Question 2

What is the most common opportunistic infection in patients with AIDS?

Accepted Answer

Candidiasis

Answer

Cryptococcosis

Answer

Tuberculosis

Answer

Aspergillosis

Question 3

What is the treatment of choice for Pneumocystis jirovecii pneumonia?

Accepted Answer

Trimethoprim/sulfamethoxazole

Answer

Erythromycin

Answer

Ofloxacin

Answer

Tetracycline

Question 4

Opisthotonus is typically seen in which of the following conditions?

Accepted Answer

Tetanus

Answer

Anthrax

Answer

Tetany

Answer

Rabies

Question 5

Dengue fever is characterized by all except?

Accepted Answer

Increased clotting time

Answer

Rash

Answer

Fever

Answer

Thrombocytopenia

Question 6

Which of the following medications used to treat severe cerebral malaria can cause hypoglycemia?

Accepted Answer

Quinine

Answer

Chloroquine

Answer

Halofantrine

Answer

Mefloquine

Question 7

Hepatitis B infection is most commonly associated with which of the following conditions?

Accepted Answer

Serum sickness

Answer

Polyarteritis nodosa

Answer

Systemic lupus erythematosus

Answer

Polymyositis

Question 8

Primary atypical pneumonia is caused by all of the following organisms, EXCEPT:

Accepted Answer

Mumps virus

Answer

Coxiella burnetii

Answer

Influenza

Answer

Measles

Question 9

Which of the following is a FALSE statement regarding Pyrexia of Unknown Origin (PUO)?

Accepted Answer

Fever persisting after 1 month of regular treatment

Answer

Cause unknown despite more than 3 days of hospitalization

Answer

Cause unknown even after 3 outpatient department (OPD) visits

Answer

Usually, fever more than 38.3 degrees Celsius

Question 10

Which of the following hepatitis infections has the worst prognosis?

Accepted Answer

Hepatitis D Virus (HDV) Superinfection on Hepatitis B Virus (HBV) Infection

Answer

Hepatitis B Virus (HBV) Infection

Answer

Hepatitis D Virus (HDV) Infection

Answer

Hepatitis B Virus (HBV) and Hepatitis D Virus (HDV) Coinfection

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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