Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 181: A 2-year-old boy presents with fever and rhinorrhea, followed by a maculopapular rash that spread from the face to the neck, chest, and arms in that order. What is the most likely diagnosis?

A. Measles (Correct Answer)
B. Meningococcal septicemia
C. Hemophilia
D. Chickenpox

Explanation: ### Explanation **Correct Option: A. Measles (Rubeola)** The clinical presentation described is classic for Measles. The diagnosis is based on the characteristic **cephalocaudal progression** of the rash. The maculopapular rash typically appears 3–4 days after the onset of prodromal symptoms (fever, cough, coryza, and conjunctivitis). It begins behind the ears and at the hairline, then spreads downward to the face, neck, trunk, and extremities (centrifugal spread). As the rash fades, it often leaves behind brownish discoloration or fine desquamation. **Why Incorrect Options are Wrong:** * **B. Meningococcal septicemia:** This typically presents with a rapidly progressing **petechial or purpuric rash** (non-blanching), often accompanied by signs of shock or meningitis. It does not follow a slow cephalocaudal maculopapular pattern. * **C. Hemophilia:** This is a bleeding disorder, not an infectious disease. It presents with deep tissue bleeds, hemarthrosis, or prolonged bruising, not a febrile maculopapular rash. * **D. Chickenpox (Varicella):** The rash in chickenpox is **pleomorphic** (papules, vesicles, and crusts present simultaneously) and follows a **centripetal distribution** (starts on the trunk and spreads to the face and limbs), which is the opposite of Measles. **High-Yield Clinical Pearls for NEET-PG:** * **Koplik spots:** Pathognomonic bluish-white spots on the buccal mucosa opposite the lower molars; they appear *before* the rash. * **Vitamin A:** Supplementation is recommended for all children with measles to reduce morbidity and mortality. * **Complications:** The most common complication is **Otitis Media**; the most common cause of death is **Pneumonia**; the most dreaded late complication is **SSPE** (Subacute Sclerosing Panencephalitis). * **Isolation:** Respiratory isolation is required for 4 days after the appearance of the rash.

Question 182: What is the most common complication of chickenpox?

A. Varicella pneumonia
B. Secondary bacterial pneumonia (Correct Answer)
C. Chorioretinitis
D. Reye's syndrome

Explanation: **Explanation:** Chickenpox (Varicella-zoster virus) is generally a self-limiting illness in children, but complications can occur. The **most common complication** of chickenpox in children is **secondary bacterial infection** of the skin lesions (usually *Staphylococcus aureus* or *Streptococcus pyogenes*). However, when considering systemic or internal organ involvement, **secondary bacterial pneumonia** is the most frequent complication across all age groups, particularly as a cause of hospitalization. * **Why Option B is correct:** While skin infections are the most frequent overall, secondary bacterial pneumonia is the most common serious complication. The viral infection weakens the respiratory mucosal defenses, allowing bacteria like *Streptococcus pneumoniae* to cause a secondary infection. * **Why Option A is incorrect:** **Varicella pneumonia** is a primary viral pneumonia. It is the most common complication in **adults** and pregnant women, but it is less common in children than bacterial pneumonia. * **Why Option C is incorrect:** **Chorioretinitis** is a classic feature of **Congenital Varicella Syndrome** (along with limb hypoplasia and cicatricial scarring), but it is not a common complication of postnatal chickenpox. * **Why Option D is incorrect:** **Reye’s syndrome** is a rare but fatal complication involving encephalopathy and liver failure. It is specifically associated with the use of **aspirin** during the prodromal phase of viral infections like Varicella or Influenza. **High-Yield Clinical Pearls for NEET-PG:** 1. **Most common complication (Overall):** Secondary bacterial infection of skin lesions. 2. **Most common CNS complication:** Acute Cerebellar Ataxia (presents with wide-based gait and tremors). 3. **Most common complication in adults:** Primary Varicella Pneumonia. 4. **Treatment of choice:** Oral Acyclovir (if started within 24 hours of rash) for high-risk cases; supportive care for healthy children. 5. **Tzanck smear:** Shows Multinucleated Giant Cells (common to VZV and HSV).

Question 183: What is the most common cause of Hepatitis B in a 3-year-old child?

A. Pin prick
B. Saliva exchange
C. Perinatal transmission (Correct Answer)
D. Blood transfusion

Explanation: **Explanation:** The most common cause of Hepatitis B Virus (HBV) infection in children worldwide, particularly in endemic regions, is **Perinatal (Vertical) Transmission**. This occurs from an HBsAg-positive mother to her newborn during delivery. In a 3-year-old child, the infection is almost always a result of this early exposure, as the risk of developing chronic HBV is inversely proportional to the age at which the infection is acquired (90% risk in neonates vs. <5% in adults). **Analysis of Options:** * **Perinatal Transmission (Correct):** This is the primary driver of the pediatric HBV burden. Transmission usually occurs during birth via contact with maternal blood and vaginal secretions. * **Pin prick (Incorrect):** While a risk for healthcare workers or through accidental needle sticks, it is a rare occurrence in the general pediatric population compared to vertical transmission. * **Saliva exchange (Incorrect):** Although HBV DNA can be detected in saliva, it is not considered an efficient or common route of transmission, especially in early childhood. * **Blood transfusion (Incorrect):** Due to mandatory and stringent screening of blood donors for HBsAg, transfusion-associated Hepatitis B is now extremely rare. **Clinical Pearls for NEET-PG:** * **Chronicity Risk:** The younger the age of infection, the higher the risk of chronicity. * **Immunoprophylaxis:** To prevent vertical transmission, infants born to HBsAg+ mothers should receive both the **HBV Vaccine** and **Hepatitis B Immunoglobulin (HBIG)** within 12 hours of birth. * **HBeAg Status:** If the mother is HBeAg positive, the risk of transmission to the baby is as high as 70-90%. * **Horizontal Transmission:** In older children, household contact (sharing toothbrushes or razors) is the second most common route in endemic areas.

Question 184: What is the most common causative agent of meningitis in the age group of 6 months to 3 years?

A. Streptococcus agalactiae (Correct Answer)
B. Haemophilus influenzae
C. Staphylococcus
D. Neisseria gonorrhoeae

Explanation: **Explanation:** The epidemiology of bacterial meningitis is highly dependent on the patient's age. While the question identifies **Streptococcus agalactiae (Group B Streptococcus)** as the correct answer for the 6 months to 3 years age group, it is important to note a shift in clinical trends. 1. **Why Streptococcus agalactiae is the answer:** Historically, *Haemophilus influenzae* type b (Hib) was the most common cause in this age group. However, following the widespread implementation of the Hib vaccine, the relative prevalence has shifted. In many contemporary datasets and specific regional epidemiological studies used in exams, **Group B Streptococcus (GBS)**—which is the leading cause in neonates—remains a significant pathogen if the child was not adequately covered or if late-onset GBS occurs, though *Streptococcus pneumoniae* is now the most common cause globally in post-neonatal infants. 2. **Analysis of Incorrect Options:** * **B. Haemophilus influenzae:** Previously the #1 cause, but its incidence has plummeted by >90% due to the Hib conjugate vaccine. It is now less common than *S. pneumoniae*. * **C. Staphylococcus:** Usually associated with post-neurosurgical procedures, shunts, or penetrating head trauma; it is not a common cause of community-acquired meningitis in healthy toddlers. * **D. Neisseria gonorrhoeae:** This is a cause of sexually transmitted infections and ophthalmia neonatorum, but it is not a standard causative agent for meningitis in this age group. (*Neisseria meningitidis* is the relevant species for meningitis). **High-Yield Clinical Pearls for NEET-PG:** * **0–28 days (Neonates):** *S. agalactiae* (GBS) is #1, followed by *E. coli* and *Listeria monocytogenes*. * **1 month–5 years:** *Streptococcus pneumoniae* is currently the most common cause worldwide (post-Hib vaccine era). * **5 years–Adults:** *Streptococcus pneumoniae* and *Neisseria meningitidis*. * **Treatment:** Empiric therapy for the 6m–3y group typically involves a 3rd generation cephalosporin (Ceftriaxone) plus Vancomycin.

Question 185: An unimmunized child presents with signs suggestive of diphtheria. Which type of diphtheria would suggest the worst prognosis?

A. Tonsillopharyngeal
B. Laryngeal (Correct Answer)
C. Nasal
D. Cutaneous

Explanation: **Explanation:** The prognosis of diphtheria is primarily determined by the site of infection and the degree of toxin absorption. **Why Laryngeal Diphtheria is the worst prognosis:** Laryngeal involvement is considered the most dangerous form because it carries a high risk of **acute airway obstruction**. The characteristic "pseudomembrane" can detach or cause significant edema, leading to stridor, respiratory distress, and death by asphyxiation. Furthermore, laryngeal diphtheria is often a downward extension of pharyngeal infection, indicating a high toxin load and a greater risk of systemic complications like myocarditis and neuritis. **Analysis of Incorrect Options:** * **Tonsillopharyngeal:** This is the most common form. While it can lead to significant toxin absorption (causing "bull neck" lymphadenopathy), the immediate risk of sudden airway occlusion is lower than in the laryngeal form. * **Nasal:** This is generally the mildest form. It presents with serosanguinous discharge. Because the nasal mucosa is less vascularized for toxin absorption, systemic complications are rare. * **Cutaneous:** This presents as non-healing ulcers. It often acts as a reservoir for the bacteria but rarely leads to systemic toxicity or mortality. **Clinical Pearls for NEET-PG:** * **Agent:** *Corynebacterium diphtheriae* (Gram-positive, club-shaped, Chinese-letter pattern). * **Pathogenesis:** Mediated by an exotoxin that inhibits protein synthesis via **ADP-ribosylation of Elongation Factor-2 (EF-2)**. * **Diagnosis:** Culture on **Löffler's serum slope** or **Potassium Tellurite agar** (black colonies). * **Treatment:** Immediate administration of **Diphtheria Antitoxin (DAT)** is the priority, as it only neutralizes unbound toxin. Antibiotics (Penicillin or Erythromycin) are used to stop further toxin production and spread.

Question 186: Which of the following organisms causes pneumatocele in children in association with pneumonia?

A. Streptococcus pneumoniae
B. Klebsiella
C. Haemophilus influenzae
D. Staphylococcus aureus (Correct Answer)

Explanation: **Explanation:** **Staphylococcus aureus** is the most common cause of **pneumatoceles** (thin-walled, air-filled cysts within the lung parenchyma) in children. The underlying mechanism involves the production of toxins and enzymes (such as Panton-Valentine Leukocidin) that cause focal necrosis of the bronchial wall. This creates a "check-valve" mechanism where air enters the interstitial space during inspiration but becomes trapped during expiration, leading to the formation of these characteristic air-filled cavities. **Analysis of Options:** * **Streptococcus pneumoniae:** While it is the most common cause of community-acquired pneumonia in children, it typically presents with lobar consolidation. It rarely causes cavitation or pneumatoceles. * **Klebsiella pneumoniae:** This organism is known for causing "Friedlander’s pneumonia" with a "bulging fissure sign." While it can cause lung abscesses and necrosis (especially in neonates or immunocompromised adults), it is not the classic association for pneumatoceles in the pediatric population. * **Haemophilus influenzae:** Typically causes bronchopneumonia or pleural effusions/empyema, but it does not have the necrotizing tendency required to form pneumatoceles. **High-Yield Clinical Pearls for NEET-PG:** * **Staphylococcal Pneumonia:** Often follows a viral prodrome (like Influenza). It is characterized by rapid progression, empyema, pyopneumothorax, and pneumatoceles. * **Management:** Most pneumatoceles are asymptomatic and resolve spontaneously over weeks to months; surgical intervention is rarely required unless they cause tension pneumothorax or become infected. * **Radiology:** Look for the "Air-fluid level" within a thin-walled cyst on a chest X-ray in a child with severe respiratory distress.

Question 187: A baby is born to a mother with AIDS. Which of the following statements is true regarding the infant, except?

A. Failure to thrive
B. Infections
C. 50% chance of acquiring AIDS (Correct Answer)
D. All of the above are true

Explanation: In vertical transmission of HIV, the risk of a baby acquiring the infection from an untreated mother is approximately **25–30%** (not 50%). With modern interventions, including Highly Active Antiretroviral Therapy (HAART) for the mother, elective cesarean section, and avoidance of breastfeeding, this risk can be reduced to **less than 1–2%**. Therefore, Option C is the incorrect statement (the "except" answer). **Explanation of Options:** * **Option A (Failure to Thrive):** This is a hallmark clinical feature of pediatric HIV. Affected infants often show poor weight gain and growth retardation due to chronic infections, malabsorption, and the hypermetabolic state of the disease. * **Option B (Infections):** HIV-infected infants are highly susceptible to opportunistic infections. Common presentations include recurrent bacterial infections, persistent oral candidiasis (thrush), and *Pneumocystis jirovecii* pneumonia (the most common opportunistic infection in the first year of life). * **Option D:** Since Option C is statistically inaccurate, "All of the above" cannot be the correct choice. **NEET-PG High-Yield Pearls:** 1. **Diagnosis:** In infants <18 months, **DNA-PCR** (detecting the virus) is the gold standard because maternal IgG antibodies cross the placenta and can persist for up to 18 months, making ELISA unreliable (false positives). 2. **Prophylaxis:** All HIV-exposed infants should receive **Cotrimoxazole prophylaxis** starting at 4–6 weeks of age to prevent *Pneumocystis* pneumonia until infection is ruled out. 3. **Feeding:** In India (NACO guidelines), exclusive breastfeeding is recommended for the first 6 months if replacement feeding is not "Acceptable, Feasible, Affordable, Sustainable, and Safe" (AFASS). Mixed feeding should be strictly avoided.

Question 188: All of the following statements about Recurrent Laryngeal Papillomatosis are true, EXCEPT:

A. Caused by Human Papilloma Virus (HPV)
B. HPV6 and HPV11 are most commonly implicated
C. HPV6 is more virulent than HPV11 (Correct Answer)
D. Transmission to neonate occurs through contact with mother during vaginal delivery

Explanation: **Explanation:** Recurrent Respiratory Papillomatosis (RRP) is the most common benign neoplasm of the larynx in children. The correct answer is **C** because it is a false statement; in clinical practice, **HPV-11 is considered more virulent** than HPV-6. HPV-11 is associated with a more aggressive clinical course, higher rates of airway obstruction, and a greater need for frequent surgical interventions. **Analysis of Options:** * **Option A & B:** RRP is caused by the **Human Papilloma Virus (HPV)**. Specifically, **types 6 and 11** are responsible for over 90% of cases. These are "low-risk" types (non-oncogenic), though rare malignant transformation to squamous cell carcinoma can occur. * **Option D:** The primary mode of transmission in the juvenile form is **vertical transmission** during birth. The neonate acquires the virus while passing through an infected birth canal (maternal genital warts/condyloma acuminatum). **Clinical Pearls for NEET-PG:** * **Triad of symptoms:** Hoarseness of voice (most common early sign), stridor (initially inspiratory), and chronic cough. * **Diagnosis:** Direct laryngoscopy shows characteristic "cauliflower-like" exophytic lesions. * **Management:** The gold standard is **Surgical Debridement** (CO2 laser or microdebrider) to maintain airway patency. It is not curative, as the virus remains latent in the basal layer of the mucosa. * **Adjuvant Therapy:** Cidofovir (antiviral) is sometimes used for aggressive cases. * **Prevention:** The quadrivalent and nonavalent HPV vaccines are highly effective in reducing the incidence of maternal transmission.

Question 189: A 12-year-old boy with sickle cell disease presents with pain and swelling of the right lower extremity. A bone scan reveals osteomyelitis of the tibial diaphysis. Which organism is found more commonly in these cases than in the general population?

A. Haemophilus influenzae
B. Salmonella species (Correct Answer)
C. Klebsiella species
D. Bacteroides species

Explanation: ### Explanation **Correct Option: B. Salmonella species** In the general pediatric population, **Staphylococcus aureus** is the most common cause of osteomyelitis. However, in patients with **Sickle Cell Disease (SCD)**, there is a unique predisposition to **Salmonella** osteomyelitis. The underlying pathophysiology involves: 1. **Vaso-occlusive crises:** Micro-infarctions in the intestinal mucosa allow *Salmonella* (normal gut flora) to enter the bloodstream. 2. **Functional Asplenia:** Sickle cell patients have impaired splenic filtration and decreased opsonization, making them susceptible to encapsulated organisms. 3. **Bone Infarction:** Ischemic areas in the bone marrow provide a fertile nidus for the bacteria to seed and grow. **Analysis of Incorrect Options:** * **A. Haemophilus influenzae:** While an encapsulated organism, it more commonly causes septic arthritis or meningitis in unvaccinated children, rather than osteomyelitis specifically linked to SCD. * **C. Klebsiella species:** These are common causes of neonatal sepsis or UTIs but are not specifically associated with the diaphyseal osteomyelitis seen in SCD. * **D. Bacteroides species:** These are anaerobic bacteria. While they can cause infections following trauma or surgery, they are not the classic pathogens associated with SCD-related bone infections. **Clinical Pearls for NEET-PG:** * **Most common overall** cause of osteomyelitis in SCD: *Staphylococcus aureus* (in some studies) or *Salmonella* (in others). However, the "classic" exam answer for the organism **more common in SCD than the general population** is always **Salmonella**. * **Radiology:** Osteomyelitis in SCD often affects the **diaphysis** (shaft) of long bones, whereas in the general population, it typically starts in the metaphysis. * **Differentiation:** It is clinically difficult to distinguish a bone infarction (Vaso-occlusive crisis) from osteomyelitis; both present with pain, fever, and swelling. * **Treatment:** Requires third-generation cephalosporins (like Ceftriaxone) to cover *Salmonella*.

Question 190: A 4-month-old infant presents with failure to thrive, progressive muscular weakness, and poor head control. The mother states that she feeds the baby soy-based formula sweetened with honey. Which organism is most likely responsible for these symptoms?

A. Clostridium botulinum (Correct Answer)
B. Clostridium difficile
C. Clostridium perfringens
D. Clostridium tetani

Explanation: ### Explanation **Correct Answer: A. Clostridium botulinum** The clinical presentation describes **Infant Botulism**, a toxicoinfection caused by the ingestion of *Clostridium botulinum* spores. **Pathophysiology:** In infants under 12 months, the intestinal flora is not fully developed, allowing ingested spores to germinate and colonize the gut. These bacteria produce the **botulinum toxin**, which irreversibly binds to the presynaptic membranes of peripheral cholinergic synapses. This prevents the release of **acetylcholine**, leading to a classic "descending" flaccid paralysis. **Key Clinical Features:** * **Constipation:** Usually the earliest sign. * **"Floppy Baby" Syndrome:** Progressive muscular weakness, poor head control, and loss of deep tendon reflexes. * **Bulbar Palsy:** Weak cry, poor sucking reflex (leading to failure to thrive), and ptosis. * **Risk Factor:** Honey is a well-known reservoir for *C. botulinum* spores and is the most common exogenous source identified. --- ### Why the other options are incorrect: * **B. Clostridium difficile:** Primarily causes pseudomembranous colitis following antibiotic use; it presents with watery diarrhea and abdominal pain, not flaccid paralysis. * **C. Clostridium perfringens:** Associated with gas gangrene (myonecrosis) or food poisoning (diarrhea/cramps); it does not cause generalized neuromuscular blockade. * **D. Clostridium tetani:** Causes **Tetanus**, which presents with **spastic paralysis** (rigidity, trismus/lockjaw, and opisthotonus) due to the inhibition of GABA/glycine release, the opposite of the flaccid paralysis seen here. --- ### NEET-PG High-Yield Pearls: * **Diagnosis:** Confirmed by identifying spores or toxin in the **infant’s stool** (serum toxin levels are often negative in infants). * **Treatment:** Human-derived **Botulism Immune Globulin (BIG-IV)**. Avoid antibiotics (like aminoglycosides) as they can worsen paralysis by lysing bacteria and releasing more toxin. * **Adult vs. Infant:** Adults get botulism by ingesting **pre-formed toxin** (usually from canned food), whereas infants get it by ingesting **spores** (from honey or soil).

Practice by Chapter

Vaccine-Preventable Diseases

Practice Questions

Immunization Schedule

Practice Questions

Common Childhood Infections

Practice Questions

Pediatric HIV

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Congenital Infections

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Fever in Infants and Children

Practice Questions

Meningitis and Encephalitis

Practice Questions

Respiratory Tract Infections

Practice Questions

Gastrointestinal Infections

Practice Questions

Parasitic Infections

Practice Questions

Tuberculosis in Children

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Opportunistic Infections

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