Infectious Diseases Practice Questions

Q: A 2-year-old girl presents with recurrent episodes of diarrhea (mucus and blood at times), hepatosplenomegaly, perianal excoriation, and resistant oral thrush. She weighs 6 kg and measures 78 cm in height. What is the most likely diagnosis?

HIV infection. ### Explanation The clinical presentation of this 2-year-old girl is highly suggestive of **Pediatric HIV infection**. The diagnosis is based on a constellation of chronic, multi-systemic findings: 1. **Failure to Thrive (FTT):** Her weight (6 kg) is significantly low for her age and height (78 cm), indicating severe wasting. 2. **Opportunistic & Recurrent Infections:** Resistant oral thrush (Candidiasis) and chronic/recurrent diarrhea (often due to *Cryptosporidium* or *Isospora*) are hallmark signs of immunodeficiency. 3. **Physical Findings:** Hepatosplenomegaly and perianal excoriation (secondary to chronic diarrhea) are common clinical markers in pediatric HIV. **Analysis of Incorrect Options:** * **A. Necrotizing enterocolitis:** Typically occurs in preterm neonates in the first few weeks of life, presenting with abdominal distension and pneumatosis intestinalis, not chronic FTT and thrush. * **B. Lactose intolerance:** While it causes osmotic diarrhea and perianal excoriation, it does not explain hepatosplenomegaly, resistant thrush, or severe systemic wasting. * **D. Campylobacter jejuni:** Causes acute bloody diarrhea (dysentery), but it is a self-limiting or acute bacterial infection and doesn't account for the chronic multi-organ involvement. **NEET-PG High-Yield Pearls:** * **Cardinal Signs:** Suspect HIV in children with "The Triad": Chronic diarrhea, Failure to Thrive, and Persistent Lymphadenopathy/Hepatosplenomegaly. * **Diagnosis:** In children ** 18 months**, **ELISA** is used. * **Most Common Opportunistic Infection:** *Pneumocystis jirovecii* pneumonia (PCP) is the most common opportunistic infection in HIV-infected infants, peaking between 3–6 months of age. * **WHO Clinical Staging:** Oral candidiasis and unexplained persistent diarrhea for >1 month place the child in Clinical Stage 3 or 4.

Q: What is the most common complication of malaria in children?

Severe malarial anemia. **Explanation:** In pediatric populations, particularly in high-transmission areas (Sub-Saharan Africa and parts of SE Asia), **Severe Malarial Anemia (SMA)** is the most frequent manifestation of severe *Plasmodium falciparum* infection. **Why Severe Malarial Anemia is the correct answer:** The pathogenesis involves a triad of: 1. **Direct Parasitization:** Destruction of infected RBCs during schizogony. 2. **Splenic Sequestration:** Removal of both infected and non-infected RBCs by the spleen. 3. **Dyserythropoiesis:** Bone marrow suppression mediated by inflammatory cytokines (TNF-α), which inhibits the production of new RBCs. In children, who have lower iron stores and higher growth demands, this leads to a rapid and profound drop in hemoglobin. **Analysis of Incorrect Options:** * **Cerebral Malaria (A):** While it is the most common cause of **death** and the most dramatic presentation, it is statistically less frequent than anemia in children. * **Respiratory Distress (B):** Often caused by metabolic acidosis (Kussmaul breathing) or pulmonary edema, it is a significant predictor of mortality but occurs less frequently than SMA. * **Hypoglycemia (D):** A common metabolic complication due to parasite glucose consumption and quinine therapy, but it is secondary to the hematological impact. **NEET-PG High-Yield Pearls:** * **Most common complication in children:** Severe Malarial Anemia. * **Most common complication in adults:** Acute Renal Failure (ARF) and Jaundice. * **Most common cause of death (overall):** Cerebral Malaria. * **WHO Definition of SMA:** Hemoglobin < 5 g/dL or Hematocrit < 15% in the presence of parasitemia. * **Drug of Choice for Severe Malaria:** Intravenous Artesunate (preferred over Quinine).

Q: Death in poliomyelitis is usually due to?

Respiratory Paralysis. **Explanation:** The primary cause of mortality in Poliomyelitis is **Respiratory Paralysis**. While the majority of polio cases are asymptomatic or mild, paralytic polio occurs in about 1% of infections. Death occurs when the virus affects the motor neurons responsible for breathing. This happens through two main mechanisms: 1. **Bulbar Polio:** The virus attacks the brainstem (medulla oblongata), paralyzing the cranial nerves and the vital respiratory control centers. 2. **Spinal Polio:** High cervical cord involvement leads to paralysis of the **phrenic nerve** (C3-C5), causing diaphragm failure, or involvement of thoracic segments leading to intercostal muscle paralysis. **Analysis of Incorrect Options:** * **Hypertension (A):** While autonomic dysfunction can occur in bulbar polio leading to blood pressure fluctuations, it is rarely the direct cause of death. * **Aspiration (C):** Bulbar involvement causes pharyngeal paralysis and loss of gag reflex, which significantly increases the risk of aspiration pneumonia. While a serious complication, the immediate cause of death in the acute phase is typically the failure of the respiratory pump itself. * **Arrhythmias (D):** Involvement of the cardiovascular centers in the medulla can lead to tachycardia or arrhythmias, but these are secondary to the profound hypoxia caused by respiratory failure. **High-Yield Pearls for NEET-PG:** * **Most common type of Polio:** Inapparent/Asymptomatic infection (91-96%). * **Most common strain causing paralysis:** Type 1 (Brunhilde). * **Eradication status:** Type 2 (1999) and Type 3 (2012) have been globally eradicated. * **Clinical Sign:** "Tripod sign" (inability to sit upright without supporting hands behind the back) indicates meningeal irritation. * **Post-Polio Syndrome:** Occurs 15–40 years after recovery due to the gradual degeneration of remaining motor neurons.

Q: Most cases of post-infection encephalitis follow which of the following?

Measles. **Explanation:** **Post-infectious encephalitis** (also known as Acute Disseminated Encephalomyelitis - ADEM) is an immune-mediated demyelinating disease of the central nervous system that typically occurs 1–2 weeks following a viral infection or vaccination. **Why Measles is the Correct Answer:** Among the childhood exanthematous illnesses, **Measles (Rubeola)** is historically and clinically the most common cause of post-infectious encephalitis. It occurs in approximately 1 in 1,000 cases of measles. The pathogenesis involves an autoimmune attack on the myelin basic protein triggered by the virus, rather than direct viral invasion of the brain parenchyma. It is characterized by sudden onset of fever and neurological deficits during the convalescent phase of the rash. **Analysis of Incorrect Options:** * **Rheumatic Fever:** This is a post-streptococcal (Group A Streptococcus) inflammatory disease affecting the heart, joints, and skin. While it can cause **Sydenham’s chorea** (involving the basal ganglia), it does not typically present as encephalitis. * **Chickenpox (Varicella):** While Varicella can cause neurological complications, the most common presentation is **Acute Cerebellar Ataxia** (post-varicella cerebellitis) rather than generalized encephalitis. * **Mumps:** Mumps is a common cause of **aseptic meningitis** and can cause direct viral encephalitis, but it is statistically less frequent than measles as a trigger for post-infectious ADEM. **NEET-PG High-Yield Pearls:** * **Subacute Sclerosing Panencephalitis (SSPE):** Do not confuse post-infectious encephalitis with SSPE. SSPE is a **late** complication (years later) caused by a persistent mutant measles virus. * **ADEM Pathological Hallmark:** Perivascular "sleeves" of demyelination. * **Most common cause of sporadic viral encephalitis:** Herpes Simplex Virus (HSV-1). * **Most common cause of epidemic encephalitis in India:** Japanese Encephalitis (JE).

Q: A child presents with tuberculosis. Steroids are not indicated in which of the following conditions?

Progressive primary pulmonary disease. **Explanation:** In the management of pediatric tuberculosis, corticosteroids are used as an adjunct to Anti-Tubercular Treatment (ATT) primarily to reduce the inflammatory response and prevent complications like fibrosis or mechanical obstruction. **Why Progressive Primary Pulmonary Disease (PPPD) is the correct answer:** PPPD refers to the direct progression of a primary focus into pneumonia or cavitation. In this condition, the primary requirement is intensive bactericidal action (ATT). Steroids have **no proven benefit** in PPPD and may theoretically interfere with the local immune response required to contain the infection. **Analysis of Incorrect Options:** * **Tuberculoma:** Steroids are indicated if there is significant perilesional edema causing increased intracranial pressure or focal neurological deficits. * **Endobronchial Tuberculosis:** Steroids are used to reduce the inflammatory edema and granulation tissue in the airway, thereby preventing bronchial obstruction and subsequent collapse or bronchiectasis. * **Massive Pleural Effusion:** While not always mandatory, steroids are indicated in massive effusions to hasten the resolution of fluid, reduce systemic symptoms (fever/pain), and prevent pleural thickening/fibrosis. **High-Yield Clinical Pearls for NEET-PG:** * **Absolute Indications for Steroids in TB:** TB Meningitis (Stage II and III) and Miliary TB (if associated with respiratory distress or hypoxia). * **Other Indications:** Pericardial effusion (to prevent constrictive pericarditis), severe phlyctenular conjunctivitis, and renal TB (to prevent ureteric strictures). * **Standard Dose:** Prednisolone 1–2 mg/kg/day for 4–6 weeks, followed by a tapering dose.

Q: MMR vaccine is recommended at which age?

15-18 months. ### Explanation The **MMR (Measles, Mumps, Rubella)** vaccine is a live attenuated vaccine. According to the **Indian Academy of Pediatrics (IAP)** and standard immunization schedules, the first dose of the MMR vaccine is recommended at **15–18 months** of age. **Why 15-18 months is correct:** While the Measles-Rubella (MR) vaccine is given earlier under the National Immunization Schedule (NIS), the specific MMR combination is traditionally administered after the first birthday. By 15 months, maternal antibodies have waned sufficiently to prevent interference with the live vaccine virus, ensuring a robust immune response. **Analysis of Incorrect Options:** * **9-12 months:** This is the age for the **1st dose of Measles/MR vaccine** under the National Immunization Schedule (NIS) in India. MMR is generally not given this early as a routine first dose in private practice/IAP schedules. * **2-3 years:** This is too late for the primary dose. However, the **2nd dose** of MMR is typically given between 4–6 years (or earlier, with a minimum gap of 4-8 weeks). * **10-19 years:** This age group is targeted for Tdap boosters or HPV vaccination, not the primary MMR series. **High-Yield Clinical Pearls for NEET-PG:** * **Route & Dose:** 0.5 ml, Subcutaneous (SC). * **Contraindications:** Pregnancy (risk of Congenital Rubella Syndrome), severe immunosuppression (e.g., low CD4 counts), and history of anaphylaxis to Neomycin or Gelatin. * **NIS vs. IAP:** Under India’s **Universal Immunization Programme (UIP)**, the **MR vaccine** is given at 9 months and 16-24 months. MMR is primarily used in private clinical practice following IAP guidelines. * **Cold Chain:** MMR is highly heat-sensitive and must be stored at +2°C to +8°C; it must be used within 4 hours of reconstitution.

Q: The rash in measles typically occurs first in which region?

Post auricular. **Explanation:** The correct answer is **Post-auricular**. Measles (Rubeola) is a highly contagious viral infection characterized by a specific sequence of clinical features. The rash in measles is a **maculopapular, erythematous, and blanching** eruption. **Why Post-auricular is correct:** The rash typically appears on the **4th day** of the illness (the eruptive phase). It characteristically starts **behind the ears (post-auricular)** and along the **hairline**. From there, it spreads in a **cephalocaudal** (head-to-toe) direction, moving downward to the face, neck, trunk, and finally the extremities (including palms and soles in severe cases). **Why other options are incorrect:** * **Forehead:** While the rash quickly involves the forehead and face, it classically originates behind the ears. * **Chest & Neck:** These areas are involved later as the rash spreads downward. The neck is usually involved on the first day of the rash, and the chest/trunk on the second day. **High-Yield Clinical Pearls for NEET-PG:** * **Koplik Spots:** These are the pathognomonic "grains of salt on a red base" found on the buccal mucosa opposite the lower second molars. They appear *before* the rash (prodromal stage). * **The 3 C’s:** The prodromal phase is marked by **C**ough, **C**oryza, and **C**onjunctivitis. * **Resolution:** The rash fades in the same order it appeared, often leaving behind **brownish discoloration** and **fine desquamation**. * **Vitamin A:** Supplementation is recommended for all children with measles to reduce morbidity and mortality. * **Most common complication:** Otitis media. * **Most common cause of death:** Pneumonia.

Q: What is the mortality rate in measles encephalitis?

10-20%. **Explanation:** Measles (Rubeola) is associated with several neurological complications, the most common being **Acute Disseminated Encephalomyelitis (ADEM)**, also known as post-measles encephalitis. This typically occurs 2–7 days after the appearance of the rash and is an immune-mediated demyelinating process. **Why 10-20% is correct:** The mortality rate for acute measles encephalitis is consistently cited in standard pediatric textbooks (like Nelson) as **10–15%**, which falls within the **10–20%** range. Beyond mortality, this condition is significant because approximately **25–40%** of survivors suffer from permanent neurological sequelae, such as intellectual disability, seizures, or deafness. **Analysis of Incorrect Options:** * **A (1-2%):** This is too low for encephalitis. This figure more closely resembles the overall case fatality rate of measles in developing countries due to respiratory complications (pneumonia). * **C & D (20-40%):** These figures are too high for acute encephalitis. While measles is severe, the acute neurological mortality rarely exceeds 20% with modern supportive care. **High-Yield Clinical Pearls for NEET-PG:** * **Most common cause of death in Measles:** Pneumonia (responsible for ~60% of deaths). * **Subacute Sclerosing Panencephalitis (SSPE):** A late, progressive degenerative complication occurring 7–10 years after infection. It is 100% fatal. * **Vitamin A:** Supplementation is mandatory in all children with measles to reduce mortality and blindness. * **Modified Measles:** Occurs in partially immune individuals; it has a longer incubation period and milder symptoms.

Q: What is the most common cause of Reye's syndrome in children?

Influenza virus. **Explanation:** **Reye’s Syndrome** is a rare but life-threatening condition characterized by acute non-inflammatory encephalopathy and fatty degeneration of the liver (microvesicular steatosis). It typically follows a viral prodrome. **Why Influenza is Correct:** The most common triggers for Reye’s syndrome are **Influenza (Type A and B)** and **Varicella (Chickenpox)**. The underlying pathophysiology involves mitochondrial dysfunction, which is severely exacerbated when a child with a viral infection is administered **Aspirin (salicylates)**. This leads to a failure of fatty acid oxidation, resulting in hyperammonemia, cerebral edema, and hepatic failure. **Analysis of Incorrect Options:** * **Polio virus:** Primarily affects the anterior horn cells of the spinal cord; it is not associated with the metabolic/mitochondrial failure seen in Reye’s. * **Measles virus:** While measles can cause Subacute Sclerosing Panencephalitis (SSPE) or acute encephalitis, it is not a classic trigger for Reye’s syndrome. * **HIV:** Causes chronic immunodeficiency and opportunistic infections but does not trigger the acute mitochondrial toxicity characteristic of Reye’s. **High-Yield Clinical Pearls for NEET-PG:** * **The "Aspirin Connection":** Always avoid Aspirin in children with viral fevers (except in Kawasaki disease). Use Acetaminophen (Paracetamol) instead. * **Biochemical Markers:** Characterized by elevated serum ammonia, increased AST/ALT, prolonged Prothrombin Time (PT), and **normal bilirubin** (a key diagnostic hint). * **Histopathology:** Liver biopsy shows **microvesicular steatosis** (fine droplets of fat) without significant inflammation. * **Clinical Sign:** Persistent, profuse vomiting followed by altered sensorium/delirium after a viral illness.

Question 1

A 2-year-old girl presents with recurrent episodes of diarrhea (mucus and blood at times), hepatosplenomegaly, perianal excoriation, and resistant oral thrush. She weighs 6 kg and measures 78 cm in height. What is the most likely diagnosis?

Accepted Answer

HIV infection

Answer

Necrotizing enterocolitis

Answer

Lactose intolerance

Answer

Campylobacter jejuni infection

Question 2

What is the most common complication of malaria in children?

Accepted Answer

Severe malarial anemia

Answer

Cerebral malaria

Answer

Respiratory distress

Answer

Hypoglycemia

Question 3

Koplik spots are described as:

Accepted Answer

A manifestation seen before cutaneous rashes but seldom observed.

Answer

The first manifestation of measles.

Answer

Rarely seen in measles.

Answer

Seen 2-3 days after cutaneous rashes.

Question 4

Death in poliomyelitis is usually due to?

Accepted Answer

Respiratory Paralysis

Answer

Hypertension

Answer

Aspiration

Answer

Arrhythmias

Question 5

Most cases of post-infection encephalitis follow which of the following?

Accepted Answer

Measles

Answer

Rheumatic fever

Answer

Chicken pox

Answer

Mumps

Question 6

A child presents with tuberculosis. Steroids are not indicated in which of the following conditions?

Accepted Answer

Progressive primary pulmonary disease

Answer

Tuberculoma

Answer

Endobronchial tuberculosis

Answer

Massive pleural effusion

Question 7

MMR vaccine is recommended at which age?

Accepted Answer

15-18 months

Answer

9-12 months

Answer

2-3 years

Answer

10-19 years

Question 8

The rash in measles typically occurs first in which region?

Accepted Answer

Post auricular

Answer

Forehead

Answer

Chest

Answer

Neck

Question 9

What is the mortality rate in measles encephalitis?

Accepted Answer

10-20%

Answer

1-2%

Answer

20-30%

Answer

30-40%

Question 10

What is the most common cause of Reye's syndrome in children?

Accepted Answer

Influenza virus

Answer

Polio virus

Answer

Measles virus

Answer

HIV

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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