Infectious Disease Practice Questions

Q: A 4-year-old boy presents with low-grade fever, inspiratory stridor, and barking cough for the past 5 days. Examination reveals a hoarse voice, a moderately inflamed pharynx, and a slightly increased respiratory rate. His chest x-ray showed subglottic narrowing appearing like a steeple. Which among the following is not indicated in the treatment of this condition?

Parenteral cefotaxime. ***Parenteral cefotaxime*** - The clinical presentation (low-grade fever, inspiratory stridor, barking cough, hoarse voice) and the **steeple sign** on chest X-ray are classic for **croup (laryngotracheobronchitis)**, which is predominantly caused by **viral infections**, not bacterial. Therefore, antibiotics like parenteral cefotaxime are generally **not indicated**. - **Cefotaxime** is a broad-spectrum antibiotic used for serious bacterial infections; its use in viral croup would be inappropriate and could contribute to antibiotic resistance. *Nebulized racemic epinephrine* - **Nebulized racemic epinephrine** is a common and effective treatment for moderate to severe croup, as it helps to **vasoconstrict** the subglottic mucosa, reducing edema and improving airflow. - It provides temporary relief from symptoms, especially stridor, by reducing swelling in the airway. *Intramuscular dexamethasone* - **Dexamethasone**, a corticosteroid, is a cornerstone of croup treatment as it reduces inflammation and edema in the airway, improving respiratory symptoms. - It can be administered orally, intravenously, or intramuscularly, and provides sustained relief, typically for 24-48 hours. *Nebulized budesonide* - **Nebulized budesonide** is an alternative corticosteroid treatment for croup that delivers anti-inflammatory medication directly to the airway. - Studies show it is equally effective to dexamethasone for mild to moderate croup, though dexamethasone is often preferred due to ease of administration and longer duration of action. *Helium oxygen mixture* - A **helium-oxygen mixture (heliox)** is a therapeutic gas that is less dense than air, which can reduce the work of breathing in patients with severe airway obstruction, such as refractory croup. - By decreasing airway turbulence, heliox can temporarily improve air movement past the narrowed subglottic area.

Q: A child presents with recurrent infections. Mediastinal imaging reveals an absent thymus gland, and further investigations show low ADA (adenosine deaminase) levels. What is the most likely diagnosis?

Severe Combined Immunodeficiency (SCID). ***Severe Combined Immunodeficiency (SCID)*** - **Recurrent infections**, an **absent thymus gland** (indicating severe T-cell deficiency), and **low ADA levels** are classic features of SCID, specifically **ADA deficiency-SCID**. - ADA deficiency leads to the accumulation of toxic metabolites that destroy **B and T lymphocytes**, severely compromising both humoral and cellular immunity. *DiGeorge syndrome* - Characterized by **thymic hypoplasia or aplasia**, leading to T-cell deficiencies and recurrent infections, similar to the absent thymus. - However, DiGeorge syndrome is typically associated with **hypocalcemia** due to parathyroid hypoplasia, and **cardiac defects**, which are not mentioned, and **low ADA levels** are not a feature. *X-linked agammaglobulinemia* - Primarily affects **B-cell development**, leading to a severe deficiency of antibodies, resulting in recurrent bacterial infections. - **T-cell function** and the **thymus gland** are typically normal in this condition, and low ADA levels are not observed. *Hyper-IgM syndrome* - Characterized by normal or elevated levels of **IgM** but very low levels of **IgG, IgA, and IgE** due to defects in B-cell class switching. - The thymus gland is generally normal, and the primary defect lies in antibody production, not T-cell development or ADA deficiency. *Wiskott-Aldrich syndrome* - An X-linked immunodeficiency presenting with recurrent infections, but classically features the triad of **thrombocytopenia with small platelets**, **eczema**, and **immunodeficiency**. - The thymus is typically present, and **low ADA levels** are not characteristic of this syndrome.

Q: A 6-year-old child presents to the emergency department with sudden onset of palpitations, shortness of breath, and dizziness. The child has no significant past medical history. On examination, the heart rate is 220 beats per minute, blood pressure is $90 / 60 \mathrm{mmHg}$, and the child appears anxious but is otherwise stable. An ECG confirms the diagnosis of paroxysmal supraventricular tachycardia (PSVT). What is the initial recommended dose of adenosine for this child?

$0.1 \mathrm{mg} / \mathrm{kg}$. ***0.1 mg/kg*** - The initial recommended dose of **adenosine** for children with **PSVT** is **0.1 mg/kg** given as a rapid intravenous bolus. - This dose is typically followed by a saline flush to ensure rapid delivery to the heart and minimize peripheral metabolism. *0.05 mg/kg* - This dose is **too low** and is below the recommended initial dose for pediatric PSVT. - While it may be safer, it is unlikely to be effective in terminating the arrhythmia and would delay definitive treatment. - The standard starting dose of 0.1 mg/kg has been established to balance efficacy with safety. *0.2 mg/kg* - This dose is typically used as a **second dose** of adenosine if the initial 0.1 mg/kg dose is ineffective in converting PSVT. - The second dose can be **doubled** (e.g., from 0.1 mg/kg to 0.2 mg/kg), with a maximum single dose of 12 mg. *0.5 mg/kg* - This dose is **too high** for the initial administration of adenosine in a pediatric patient and could lead to significant side effects like profound bradycardia or asystole. - Gradual dose escalation is crucial to balance efficacy with safety in children. *1.0 mg/kg* - This dose is **excessively high** for pediatric adenosine administration and is not recommended as an initial or even subsequent dose. - Such a dose would greatly increase the risk of adverse cardiovascular effects.

Q: A 2 year old child came with watery diarrhea. Electron Microscopy (EM) Image is shown here. Choose the correct pathogen.

Rota virus. ***Rota virus*** - The electron micrograph shows **double-layered viral particles** with a distinct wheel-like appearance, characteristic of **Rotavirus**, a major cause of severe watery diarrhea in young children. - Rotavirus is the most common cause of **severe dehydrating diarrhea** in infants and young children worldwide. *Norwalk virus* - Norwalk virus (now commonly referred to as **Norovirus**) particles are typically **smaller** and have an **amorphous** or indistinct surface morphology compared to the clearly structured Rotavirus. - Norovirus causes acute gastroenteritis but its electron microscopic appearance is less distinct and lacks the double-shelled structure seen here. *Adenovirus* - Adenoviruses are **larger, non-enveloped DNA viruses** with a distinct **icosahedral capsid** structure, often appearing hexagonal or pentagonal with prominent 'spikes' at the vertices. - While adenoviruses can cause gastroenteritis, their EM appearance is easily distinguishable from the image provided. *Astrovirus* - Astroviruses are **small, non-enveloped RNA viruses** that appear as **smooth-surfaced, star-shaped particles** on electron microscopy (hence the name "astro"). - They cause gastroenteritis in young children but lack the characteristic double-layered wheel-like structure of rotavirus. *ECHO virus* - ECHO viruses (Enteric Cytopathic Human Orphan viruses) are **picornaviruses**, which are very **small, non-enveloped RNA viruses** with an icosahedral shape. - Their EM image would show much smaller, less complex particles without the characteristic double-layered structure of rotavirus.

Question 1

A 3-day-old term male neonate developed progressive respiratory distress and cyanosis unresponsive to supplemental oxygen delivered by nasal cannula. On examination, the cardiac point of maximal impulse is located at the right sternal border, and breath sounds are diminished over the left hemithorax. The abdomen appears scaphoid. Which of the following is the most appropriate immediate next step in management?

Accepted Answer

Emergent endotracheal intubation and surgical consultation for operative repair

Answer

Bag-mask ventilation with 100% oxygen to improve pre-ductal saturations

Answer

Needle decompression of the left hemithorax to relieve tension pneumothorax

Answer

Prostaglandin E1 infusion to maintain ductal patency pending echocardiogram

Answer

High-frequency oscillatory ventilation to reduce barotrauma prior to transfer

Question 2

A 4-year-old boy presents with low-grade fever, inspiratory stridor, and barking cough for the past 5 days. Examination reveals a hoarse voice, a moderately inflamed pharynx, and a slightly increased respiratory rate. His chest x-ray showed subglottic narrowing appearing like a steeple. Which among the following is not indicated in the treatment of this condition?

Accepted Answer

Parenteral cefotaxime

Answer

Nebulized racemic epinephrine

Answer

Intramuscular dexamethasone

Answer

Helium oxygen mixture

Answer

Nebulized budesonide

Question 3

A child presents with recurrent infections. Mediastinal imaging reveals an absent thymus gland, and further investigations show low ADA (adenosine deaminase) levels. What is the most likely diagnosis?

Accepted Answer

Severe Combined Immunodeficiency (SCID)

Answer

DiGeorge syndrome

Answer

X-linked agammaglobulinemia

Answer

Hyper-IgM syndrome

Answer

Wiskott-Aldrich syndrome

Question 4

A 6-year-old child presents to the emergency department with sudden onset of palpitations, shortness of breath, and dizziness. The child has no significant past medical history. On examination, the heart rate is 220 beats per minute, blood pressure is $90 / 60 \mathrm{mmHg}$, and the child appears anxious but is otherwise stable. An ECG confirms the diagnosis of paroxysmal supraventricular tachycardia (PSVT). What is the initial recommended dose of adenosine for this child?

Accepted Answer

$0.1 \mathrm{mg} / \mathrm{kg}$

Answer

$0.2 \mathrm{mg} / \mathrm{kg}$

Answer

$0.5 \mathrm{mg} / \mathrm{kg}$

Answer

$1.0 \mathrm{mg} / \mathrm{kg}$

Answer

$0.05 \mathrm{mg} / \mathrm{kg}$

Question 5

A 2 year old child came with watery diarrhea. Electron Microscopy (EM) Image is shown here. Choose the correct pathogen.

Accepted Answer

Rota virus

Answer

Norwalk virus

Answer

Adenovirus

Answer

ECHO virus

Answer

Astrovirus

Infectious Disease — MCQs

Infectious Disease — MCQs

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