Infectious Diseases — MCQs

A 3-year-old child presented with fatigue, malaise, fever, sore throat, headache, nausea, abdominal pain, and myalgia. On examination, generalized lymphadenopathy, hepatosplenomegaly, tonsillar enlargement, palatal petechiae, rashes, and edema of the eyelids were noted. In which of the following conditions would this presentation NOT occur?

Q330Medium

A child presents with a lesion on the buttocks that has been present for 2 years, spreading peripherally with central scarring and is asymptomatic. What is the most likely diagnosis?

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 321: All of the following statements are true about Erythema infectiosum except:

A. The causative agent is Parvovirus B19.
B. This disease is also known as Roseola infantum. (Correct Answer)
C. A reticulate lacy exanthem may be noted on the trunk and extremities.
D. Clinical features are usually seen in healthy individuals.

Explanation: **Explanation:** The correct answer is **B** because **Erythema infectiosum** (Fifth Disease) and **Roseola infantum** (Sixth Disease) are two distinct clinical entities caused by different viruses. 1. **Why Option B is the correct answer (False statement):** * **Erythema infectiosum** is caused by **Parvovirus B19**. * **Roseola infantum** (Exanthema subitum) is caused by **Human Herpesvirus 6 (HHV-6)** and occasionally HHV-7. Roseola is characterized by high fever for 3–5 days, followed by the sudden appearance of a rash *after* the fever subsides. 2. **Analysis of other options (True statements):** * **Option A:** Parvovirus B19 is indeed the causative agent. It is a single-stranded DNA virus that targets erythroid progenitor cells. * **Option C:** The rash of Erythema infectiosum typically follows a classic progression: it starts with an erythematous "slapped-cheek" appearance, followed by a **reticulate (lace-like) maculopapular rash** on the trunk and extremities. * **Option D:** In immunocompetent (healthy) individuals, the disease is usually mild and self-limiting. **High-Yield Clinical Pearls for NEET-PG:** * **Infectivity:** Patients are infectious *before* the onset of the rash. Once the rash appears, the child is no longer contagious. * **Aplastic Crisis:** Parvovirus B19 can cause a transient aplastic crisis in patients with high red cell turnover (e.g., Sickle Cell Anemia, Hereditary Spherocytosis). * **Pregnancy:** Infection in pregnancy can lead to **Hydrops fetalis** due to severe fetal anemia. * **Arthropathy:** In adults (especially females), Parvovirus B19 often presents with symmetrical small joint arthritis resembling Rheumatoid Arthritis.

Question 322: Hutchinson's triad is a classic sign of congenital syphilis. Which of the following is NOT a component of Hutchinson's triad?

A. Interstitial keratitis
B. Notched incisors
C. Deafness
D. Cataracts (Correct Answer)

Explanation: **Explanation:** Hutchinson’s triad is a pathognomonic clinical finding associated with **Late Congenital Syphilis** (manifesting after 2 years of age). It represents the permanent sequelae of *Treponema pallidum* infection during fetal development. **Why Cataracts is the correct answer:** Cataracts are **not** a component of Hutchinson’s triad. While ocular involvement is common in congenital syphilis, it typically manifests as interstitial keratitis or chorioretinitis. Cataracts are more characteristically associated with **Congenital Rubella Syndrome** (along with sensorineural deafness and PDA). **Analysis of the Triad Components:** * **Interstitial Keratitis (Option A):** This is an inflammatory condition of the corneal stroma. It usually appears between ages 5 and 15, leading to corneal scarring and potential blindness if untreated. * **Notched Incisors (Option B):** Also known as **Hutchinson’s teeth**, these are permanent upper central incisors that are peg-shaped, widely spaced, and notched at the biting edge. * **Deafness (Option C):** This refers specifically to **Sensorineural hearing loss** caused by eighth cranial nerve (vestibulocochlear) involvement. It often develops suddenly around puberty. **High-Yield Clinical Pearls for NEET-PG:** * **Early Congenital Syphilis (<2 years):** Look for snuffles (persistent rhinitis), pemphigus syphiliticus (bullous rash on palms/soles), and Parrot’s pseudoparalysis (due to osteochondritis). * **Other Late Signs:** Mulberry molars (rudimentary cusps on first molars), Saber shins (anterior bowing of the tibia), and Saddle nose deformity. * **Screening:** VDRL/RPR are used for screening; FTA-ABS or TP-PA are confirmatory.

Question 323: What is the most common cause of death in measles patients?

A. Encephalitis
B. Meningitis
C. Dehydration
D. Pneumonia (Correct Answer)

Explanation: **Explanation:** **Pneumonia** is the most common cause of death associated with measles in children, accounting for approximately 60% of measles-related fatalities. Measles virus causes profound immunosuppression by depleting T-lymphocytes and suppressing the immune response for weeks to months. This predisposes patients to secondary bacterial infections (most commonly *S. pneumoniae*, *H. influenzae*, and *S. aureus*) or primary giant cell pneumonia (Hecht’s pneumonia) caused by the virus itself. **Analysis of Incorrect Options:** * **Encephalitis:** While Acute Disseminated Encephalomyelitis (ADEM) and Subacute Sclerosing Panencephalitis (SSPE) are severe neurological complications, they occur much less frequently than respiratory complications. * **Meningitis:** This is not a classic or common complication of measles. Neurological involvement typically presents as encephalitis rather than isolated meningitis. * **Dehydration:** While diarrhea is the most common *complication* of measles overall (especially in developing countries), it is secondary to pneumonia as a cause of mortality. **High-Yield Clinical Pearls for NEET-PG:** * **Most common complication:** Diarrhea. * **Most common cause of death:** Pneumonia. * **Most common CNS complication:** Febrile seizures. * **Most common cause of long-term neurological mortality:** SSPE (occurs 7–10 years after infection; characterized by high titers of measles antibody in CSF). * **Vitamin A supplementation:** Essential in all children with measles to reduce the severity of complications and mortality. * **Koplik spots:** Pathognomonic sign found on the buccal mucosa opposite the lower second molars during the pre-eruptive stage.

Question 324: Which organism commonly causes diarrhea in young children?

A. Rotavirus (Correct Answer)
B. Calicivirus
C. E. coli
D. Staphylococcus

Explanation: **Explanation:** **Correct Answer: A. Rotavirus** Rotavirus is the **most common cause of severe dehydrating diarrhea** in infants and young children worldwide (typically aged 6 months to 2 years). It belongs to the *Reoviridae* family and primarily infects the mature enterocytes of the small intestine, leading to malabsorption and osmotic diarrhea. A key high-yield mechanism is the action of the **NSP4 enterotoxin**, which induces secretory diarrhea by increasing intracellular calcium. **Analysis of Incorrect Options:** * **B. Calicivirus (e.g., Norovirus):** While a common cause of viral gastroenteritis, it is more frequently associated with **outbreaks in all age groups** (schools, cruise ships, nursing homes) rather than being the primary cause specifically in young children. * **C. E. coli:** While Enterotoxigenic *E. coli* (ETEC) is a leading cause of "Traveler’s diarrhea" and pediatric diarrhea in developing countries, viral etiologies (Rotavirus) remain more prevalent globally for the pediatric age group. * **D. Staphylococcus:** *Staphylococcus aureus* causes **food poisoning** via preformed enterotoxins. It presents with rapid-onset vomiting (1–6 hours after ingestion) rather than the prolonged diarrheal illness seen in children. **High-Yield Clinical Pearls for NEET-PG:** * **Seasonality:** Rotavirus peaks during **winter months** (temperate climates). * **Vaccination:** Two oral live-attenuated vaccines are part of the Universal Immunization Programme (UIP) in India: **Rotavac** (116E strain) and **RotaSIIL**. * **Management:** The cornerstone of treatment is **ORS and Zinc supplementation** (20 mg/day for 14 days; 10 mg for infants <6 months) to reduce the duration and severity of episodes.

Question 325: All are features of Pertussis except –

A. Encephalopathy
B. Cerebellar Ataxia (Correct Answer)
C. Subconjunctival hemorrhage
D. Bronchiectasis

Explanation: **Explanation:** Pertussis (Whooping Cough), caused by *Bordetella pertussis*, is characterized by severe paroxysms of coughing. The complications of Pertussis are primarily divided into those caused by **increased intrathoracic/intra-abdominal pressure** and those caused by **toxin-mediated effects**. **Why Cerebellar Ataxia is the Correct Answer:** Cerebellar ataxia is **not** a recognized feature of Pertussis. While Pertussis can involve the central nervous system (CNS), it typically manifests as encephalopathy. Ataxia is more commonly associated with viral infections like Varicella (post-infectious cerebellitis). **Analysis of Other Options:** * **Encephalopathy (Option A):** This is a known severe neurologic complication. It is thought to be caused by hypoxia during coughing fits, cerebral edema, or toxin-mediated effects. It presents as seizures or altered consciousness. * **Subconjunctival Hemorrhage (Option B):** During the paroxysmal stage, the intense pressure generated by forceful coughing causes the rupture of small capillaries. This leads to subconjunctival hemorrhages, epistaxis, and petechiae on the face/neck. * **Bronchiectasis (Option D):** Chronic or severe Pertussis can lead to secondary bacterial pneumonia and localized airway destruction, eventually resulting in bronchiectasis as a long-term pulmonary complication. **High-Yield Clinical Pearls for NEET-PG:** * **Stages:** Catarrhal (most infectious), Paroxysmal (whooping cough), and Convalescent. * **Hematology:** Characterized by **absolute lymphocytosis** (due to Lymphocytosis Promoting Factor), which is a rare finding in bacterial infections. * **Drug of Choice:** Macrolides (Azithromycin is preferred in infants). * **Gold Standard Diagnosis:** Culture on **Regan-Lowe** or **Bordet-Gengou** medium. * **Post-exposure Prophylaxis:** Recommended for all household contacts regardless of vaccination status.

Question 326: What is the most likely diagnosis in a neonate presenting with a "Hutchinson's triad"?

A. CMV inclusion disease
B. Ectodermal dysplasia
C. Congenital syphilis (Correct Answer)
D. Hyper IgE syndrome

Explanation: **Explanation:** The correct answer is **Congenital Syphilis**. Hutchinson’s triad is a classic clinical sign pathognomonic for late congenital syphilis (presenting after 2 years of age). It consists of: 1. **Hutchinson’s teeth:** Blunted, notched permanent incisors. 2. **Interstitial keratitis:** Inflammation of the corneal stroma leading to scarring and potential blindness. 3. **Sensorineural hearing loss:** Due to eighth cranial nerve involvement. **Analysis of Incorrect Options:** * **CMV Inclusion Disease:** This is the most common congenital infection. It typically presents with a "blueberry muffin" rash, periventricular calcifications, microcephaly, and chorioretinitis, rather than dental or corneal involvement. * **Ectodermal Dysplasia:** This is a genetic disorder affecting structures derived from the ectoderm. While it features dental abnormalities (hypodontia or peg-shaped teeth), it lacks the keratitis and deafness seen in the triad and is associated with anhidrosis and sparse hair. * **Hyper IgE Syndrome (Job Syndrome):** This is an immunodeficiency characterized by "cold" staphylococcal abscesses, eczema, and retained primary teeth, but it does not present with the specific components of Hutchinson’s triad. **NEET-PG High-Yield Pearls:** * **Early Congenital Syphilis (<2 years):** Look for snuffles (persistent rhinitis), palmoplantar peeling/rash, and **Wimberger’s sign** (metaphyseal erosion of the medial proximal tibia). * **Late Congenital Syphilis (>2 years):** Look for **Saber shins**, Mulberry molars, Clutton’s joints (painless knee swelling), and Saddle nose deformity. * **Screening:** VDRL/RPR (Nontreponemal tests). * **Treatment of Choice:** Parenteral Penicillin G.

Question 327: What is the most important element in the treatment of diphtheria?

A. Antitoxin (Correct Answer)
B. Tetracycline
C. Erythromycin
D. Penicillin

Explanation: **Explanation:** The primary pathology in diphtheria is caused by the potent **exotoxin** produced by *Corynebacterium diphtheriae*. This toxin inhibits protein synthesis, leading to local tissue necrosis (pseudomembrane formation) and systemic complications like myocarditis and neuritis. Once the toxin binds to host cell receptors, it becomes irreversible. Therefore, the **most important** and life-saving element of treatment is the **Diphtheria Antitoxin (DAT)**. DAT works by neutralizing the circulating (unbound) toxin in the bloodstream before it can enter the cells. **Why the other options are incorrect:** * **Antibiotics (Erythromycin and Penicillin):** While essential, they are **secondary** to antitoxin. Antibiotics serve to stop further toxin production by killing the bacteria, prevent the spread of the organism to others, and treat the carrier state. They do not neutralize the toxin already present in the system. **Erythromycin** is generally considered the drug of choice for eradication. * **Tetracycline:** This is not a first-line agent for diphtheria and is less effective than macrolides or penicillins. **High-Yield Clinical Pearls for NEET-PG:** * **Schick Test:** Used to determine the immune status of an individual toward diphtheria. * **Loffler’s Serum Slope/Tellurite Medium:** Specific culture media used for growth (colonies appear grey-black on Tellurite). * **Albert’s Stain:** Used to demonstrate metachromatic (volutin) granules. * **Treatment Priority:** In clinical practice, DAT should be administered as soon as a clinical diagnosis is made, without waiting for laboratory confirmation, as delay increases the risk of mortality.

Question 328: A woman with a history of repeated abortions gave birth to a low birth weight baby. The child is having rashes over palms and rhinitis. What is the most probable diagnosis?

A. Congenital HIV
B. Congenital syphilis (Correct Answer)
C. Congenital rubella
D. Pemphigus

Explanation: **Explanation:** The clinical presentation of low birth weight, **rhinitis (snuffles)**, and **rashes over the palms and soles** in a neonate, combined with a maternal history of **repeated abortions**, is a classic triad for **Congenital Syphilis**. 1. **Why Congenital Syphilis is correct:** * **Rhinitis (Snuffles):** This is often the earliest clinical sign, characterized by a highly infectious, white/bloody nasal discharge. * **Palmar/Plantar Rash:** The rash in syphilis typically involves the palms and soles; it may be maculopapular or vesiculobullous (Pemphigus syphiliticus). * **Obstetric History:** *Treponema pallidum* crosses the placenta, often leading to late-term abortions, stillbirths, or prematurity. 2. **Why other options are incorrect:** * **Congenital HIV:** Usually asymptomatic at birth. Clinical features like failure to thrive and opportunistic infections develop later in infancy. * **Congenital Rubella:** Characterized by the "Gregg’s Triad": Cataracts, Sensorineural hearing loss, and Congenital Heart Disease (PDA). It also presents with a "Blueberry muffin" rash, not palmar rhinitis. * **Pemphigus:** While "Pemphigus syphiliticus" refers to the syphilitic rash, "Pemphigus" alone usually refers to an autoimmune blistering disease (Pemphigus vulgaris), which is extremely rare in neonates and not associated with rhinitis or abortions. **High-Yield Clinical Pearls for NEET-PG:** * **Early Congenital Syphilis (<2 years):** Snuffles, palmar/plantar rash, hepatosplenomegaly, and **Wimberger’s sign** (metaphyseal erosion of the medial proximal tibia). * **Late Congenital Syphilis (>2 years):** Hutchinson’s teeth, Mulberry molars, Interstitial keratitis, and Eighth nerve deafness (**Hutchinson’s Triad**). * **Screening:** VDRL/RPR (Nonspecific); **Confirmation:** FTA-ABS or TP-PA (Specific). * **Treatment of Choice:** Intravenous Penicillin G for 10 days.

Question 329: A 3-year-old child presented with fatigue, malaise, fever, sore throat, headache, nausea, abdominal pain, and myalgia. On examination, generalized lymphadenopathy, hepatosplenomegaly, tonsillar enlargement, palatal petechiae, rashes, and edema of the eyelids were noted. In which of the following conditions would this presentation NOT occur?

A. X-linked agammaglobulinemia (Correct Answer)
B. Multiple myeloma
C. DiGeorge syndrome
D. Wiskott-aldrich syndrome

Explanation: **Explanation:** The clinical presentation described—fever, sore throat, generalized lymphadenopathy, hepatosplenomegaly, tonsillar enlargement, and palatal petechiae—is classic for **Infectious Mononucleosis (IM)**, most commonly caused by the **Epstein-Barr Virus (EBV)**. **Why X-linked Agammaglobulinemia (XLA) is the correct answer:** EBV specifically infects **B-lymphocytes** by binding to the **CD21 receptor**. In X-linked Agammaglobulinemia (Bruton’s), there is a mutation in the *BTK* gene, leading to a failure of B-cell maturation. Consequently, patients with XLA have a near-total **absence of circulating B-cells**. Since the host cells required for EBV infection and replication are missing, these patients do not manifest the typical clinical syndrome of Infectious Mononucleosis. **Analysis of Incorrect Options:** * **Multiple Myeloma:** While a plasma cell dyscrasia, these patients still possess B-lymphocytes that can be infected by EBV. * **DiGeorge Syndrome:** This is a T-cell deficiency (thymic hypoplasia). Since B-cell numbers are generally preserved, EBV can infect the B-cells and produce the described clinical features. * **Wiskott-Aldrich Syndrome:** This is a combined immunodeficiency affecting both T and B cells, but B-cells are present; therefore, the clinical manifestation of IM can occur. **High-Yield Clinical Pearls for NEET-PG:** * **EBV Triad:** Fever, Pharyngitis, and Lymphadenopathy (typically posterior cervical). * **Hoagland Sign:** Early transient bilateral upper eyelid edema (seen in ~10-15% of IM cases). * **Diagnostic Test:** Monospot test (Heterophile antibodies) or atypical lymphocytosis (Downey cells) on peripheral smear. * **Warning:** Administration of Ampicillin/Amoxicillin in a patient with IM often results in a characteristic maculopapular rash.

Question 330: A child presents with a lesion on the buttocks that has been present for 2 years, spreading peripherally with central scarring and is asymptomatic. What is the most likely diagnosis?

A. Erythema annulare centrifugum (Correct Answer)
B. Erythema migrans
C. Erythema marginatum
D. Erythema gyratum

Explanation: **Explanation:** The clinical presentation of a long-standing (2 years), slow-growing, annular lesion with **peripheral spread and central clearing/scarring** is characteristic of **Erythema Annulare Centrifugum (EAC)**. 1. **Why EAC is correct:** EAC is a reactive skin condition (often triggered by infections, drugs, or malignancies) characterized by erythematous, ring-shaped lesions. The "centrifugal" spread means it expands outward while the center heals. The chronic duration (years) and asymptomatic nature are hallmark features that distinguish it from acute inflammatory rashes. 2. **Why other options are incorrect:** * **Erythema Migrans:** This is the pathognomonic rash of **Lyme disease** (Borrelia burgdorferi). It expands rapidly over days to weeks (not years) and is typically associated with systemic symptoms like fever and lymphadenopathy. * **Erythema Marginatum:** This is a major Jones criterion for **Acute Rheumatic Fever**. It is a transient, evanescent (comes and goes quickly), pink, non-pruritic rash. It would not persist for 2 years. * **Erythema Gyratum Repens:** This is a paraneoplastic syndrome (often associated with lung cancer) characterized by a "wood-grain" appearance. It moves very rapidly (up to 1 cm per day), unlike the slow progression described here. **High-Yield Clinical Pearls for NEET-PG:** * **EAC "Trailing Scale":** A classic diagnostic sign of the superficial variant of EAC is a thin white scale just inside the advancing edge. * **Differential Diagnosis:** Always differentiate annular lesions from **Tinea Corporis** (which is itchy and has an active scaling border) [2] and **Granuloma Annulare** (which lacks scales). [1] * **Erythema Marginatum** is associated with **Rheumatic Fever**, while **Erythema Multiforme** is often associated with **HSV** or **Mycoplasma**.

Practice by Chapter

Vaccine-Preventable Diseases

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Immunization Schedule

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Common Childhood Infections

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Pediatric HIV

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Congenital Infections

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Fever in Infants and Children

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Meningitis and Encephalitis

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Respiratory Tract Infections

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Gastrointestinal Infections

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Parasitic Infections

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Tuberculosis in Children

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Opportunistic Infections

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