Infectious Diseases Practice Questions

Q: What is this teeth abnormality?

Hutchinson's teeth. ***Hutchinson's teeth*** - **Notched, peg-shaped upper central incisors** with a distinctive **screwdriver appearance** are pathognomonic of congenital syphilis. - Part of **Hutchinson's triad** which includes **interstitial keratitis**, **eighth nerve deafness**, and these characteristic dental abnormalities. *Mulberry molars* - **Crown-shaped molars** with multiple **cuspal projections** resembling a mulberry, also seen in congenital syphilis. - Affects **first molars** specifically, not the **central incisors** as shown in the characteristic appearance described. *Natal teeth* - **Teeth present at birth** or erupting within the first month of life, typically **lower central incisors**. - These are **normal-shaped teeth** that appear prematurely, not malformed or notched teeth. *Supernumerary teeth* - **Extra teeth** beyond the normal dental formula, most commonly **mesiodens** (extra central incisor). - These are **additional teeth** rather than **malformed existing teeth** with characteristic notching pattern.

Q: Trans-placental spread is least associated with which of the following infections?

Herpes simplex virus (HSV). **Explanation:** The core concept tested here is the **timing and mode of vertical transmission**. Vertical transmission can occur in three ways: *in utero* (trans-placental), *intrapartum* (during delivery), or *postpartum* (breastfeeding). **Why HSV is the correct answer:** While Herpes Simplex Virus (HSV) can occasionally cause congenital infection via the placenta (rarely leading to skin scarring and microcephaly), the vast majority (**85-90%**) of neonatal HSV infections are acquired **intrapartum**. This occurs through direct contact with infected maternal vaginal secretions during birth. Therefore, among the options provided, HSV is the *least* associated with trans-placental spread. **Analysis of incorrect options:** * **Rubella:** This is a classic **TORCH** infection. It is primarily transmitted **trans-placentally**, especially during the first trimester, leading to Congenital Rubella Syndrome (CRS). * **HIV:** Transmission can occur at all stages, but **trans-placental** spread (in utero) and breastfeeding are significant routes. Without intervention, the risk of trans-placental transmission is high. * **HBV:** While most HBV in endemic areas is acquired intrapartum, **trans-placental** transmission does occur, particularly if the mother has high viral loads or is HBeAg positive. **NEET-PG High-Yield Pearls:** * **HSV:** Most common route of neonatal infection is **birth canal contact** (Intrapartum). * **CMV:** The most common cause of **congenital** (trans-placental) viral infection worldwide. * **Toxoplasmosis:** The risk of trans-placental transmission **increases** with gestational age, but the **severity** of fetal damage decreases. * **Zika Virus:** A significant emerging cause of trans-placental infection leading to microcephaly.

Q: What is the drug of choice for pertussis in children?

Azithromycin. **Explanation:** The drug of choice for the treatment and post-exposure prophylaxis of **Pertussis (Whooping Cough)**, caused by *Bordetella pertussis*, is **Azithromycin**. **1. Why Azithromycin is the Correct Choice:** Macrolides are the mainstay of therapy as they eradicate the bacteria from the nasopharynx, reducing transmission. **Azithromycin** is preferred over other macrolides (like Erythromycin) in children because: * It has a shorter course (5 days) and better compliance. * It is better tolerated with fewer gastrointestinal side effects. * Most importantly, it has the **lowest risk of causing Infantile Hypertrophic Pyloric Stenosis (IHPS)**, making it the safest choice for neonates and young infants. **2. Why Other Options are Incorrect:** * **Erythromycin:** While effective, it requires a 14-day course and is strongly associated with the development of **IHPS** in infants under 1 month of age. * **Penicillin & Ampicillin:** *Bordetella pertussis* is a Gram-negative coccobacillus that is inherently resistant to penicillins in a clinical setting. These drugs do not shorten the course of the disease or reduce infectivity. **3. High-Yield Clinical Pearls for NEET-PG:** * **Treatment Goal:** Antibiotics are most effective during the **Catarrhal stage**. Once the **Paroxysmal stage** (whooping cough) begins, antibiotics do not significantly alter the clinical course but are still given to limit the spread. * **Alternative:** For patients who cannot tolerate macrolides or are >2 months old with macrolide resistance, **Trimethoprim-Sulfamethoxazole (TMP-SMX)** is the second-line agent. * **Prophylaxis:** All household and close contacts should receive post-exposure prophylaxis with Azithromycin, regardless of their vaccination status.

Q: A 5-year-old boy presents with a sore throat for the last two days. On examination, he has a greyish-white pseudomembrane around his tonsils. Diphtheria is suspected. His brother received his last booster 22 months ago. What prophylactic measure should be adopted for the brother?

Nothing is required. ### Explanation The correct answer is **B. Nothing is required.** **1. Why the correct answer is right:** Management of close contacts in Diphtheria depends on their immunization status. According to standard guidelines (including IAP and CDC), a contact is considered **fully protected** if they have received a complete primary series and a booster dose within the last **5 years**. In this case, the brother received his last booster **22 months ago** (less than 2 years). Since he is within the 5-year window of high immunity, he does not require a booster dose or chemoprophylaxis, provided he remains asymptomatic and can be monitored. **2. Why the incorrect options are wrong:** * **Option A:** Oral erythromycin (or IM Penicillin G) is indicated for **unvaccinated** or **under-vaccinated** close contacts, or those whose last booster was >5 years ago. * **Option C:** Diphtheria Antitoxin (ADS) is used for **treatment** of active cases, never for prophylaxis of contacts, due to the risk of serum sickness and anaphylaxis. * **Option D:** A booster dose of Diphtheria toxoid is indicated for fully immunized contacts only if their last dose was **more than 5 years ago**. **3. Clinical Pearls for NEET-PG:** * **Causative Agent:** *Corynebacterium diphtheriae* (Gram-positive, club-shaped, Chinese-letter pattern). * **The Membrane:** The pseudomembrane is tough, leathery, and **bleeds on attempt to remove** (distinguishing it from follicular tonsillitis). * **Schick Test:** Historically used to determine susceptibility to diphtheria (Positive = Susceptible). * **Drug of Choice (Treatment):** Erythromycin is the preferred antibiotic to stop toxin production and clear the carrier state, but **Antitoxin** is the mainstay of life-saving therapy. * **Carrier State:** Erythromycin for 7–10 days is used to treat carriers.

Q: 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?

Measles. ### 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.

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

Perinatal transmission. **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.

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

Laryngeal. **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.

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

Staphylococcus aureus. **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.

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

50% chance of acquiring AIDS. 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 1

What is this teeth abnormality?

Accepted Answer

Hutchinson's teeth

Answer

Mulberry molars

Answer

Natal teeth

Answer

Supernumerary teeth

Question 2

Trans-placental spread is least associated with which of the following infections?

Accepted Answer

Herpes simplex virus (HSV)

Answer

Hepatitis B virus (HBV)

Answer

Rubella virus

Answer

Human immunodeficiency virus (HIV)

Question 3

What is the immediate treatment for peripheral circulatory failure in Dengue Shock Syndrome?

Accepted Answer

Intravenous high dose of Dexamethasone

Answer

Intravenous Dextrose Saline

Answer

Intravenous crystalloid infusion

Answer

Intravenous Dopamine + Dobutamine

Question 4

What is the drug of choice for pertussis in children?

Accepted Answer

Azithromycin

Answer

Penicillin

Answer

Erythromycin

Answer

Ampicillin

Question 5

A 5-year-old boy presents with a sore throat for the last two days. On examination, he has a greyish-white pseudomembrane around his tonsils. Diphtheria is suspected. His brother received his last booster 22 months ago. What prophylactic measure should be adopted for the brother?

Accepted Answer

Nothing is required

Answer

Prophylaxis with oral erythromycin

Answer

Prophylaxis with erythromycin and diphtheria antitoxin

Answer

Immunize with booster of diphtheria toxoid

Question 6

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?

Accepted Answer

Measles

Answer

Meningococcal septicemia

Answer

Hemophilia

Answer

Chickenpox

Question 7

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

Accepted Answer

Perinatal transmission

Answer

Pin prick

Answer

Saliva exchange

Answer

Blood transfusion

Question 8

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

Accepted Answer

Laryngeal

Answer

Tonsillopharyngeal

Answer

Nasal

Answer

Cutaneous

Question 9

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

Accepted Answer

Staphylococcus aureus

Answer

Streptococcus pneumoniae

Answer

Klebsiella

Answer

Haemophilus influenzae

Question 10

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

Accepted Answer

50% chance of acquiring AIDS

Answer

Failure to thrive

Answer

Infections

Answer

All of the above are true

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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