Infectious Diseases Practice Questions

Q: A patient presents with fever, cough, and headache. On the fourth day of illness, a rash develops. What is the probable diagnosis?

Measles. **Explanation:** The clinical presentation of fever, cough, and headache followed by the appearance of a rash on the **fourth day** is a classic hallmark of **Measles (Rubeola)**. In Measles, the illness follows a predictable timeline: a 3-day prodromal phase characterized by the "3 Cs" (Cough, Coryza, and Conjunctivitis) and high-grade fever. The maculopapular rash typically appears on the **4th day**, starting behind the ears and spreading cephalocaudally (head to toe). **Why other options are incorrect:** * **Mumps:** Primarily presents with painful parotid swelling (parotitis). While fever and headache occur, a generalized maculopapular rash is not a standard clinical feature. * **Smallpox:** The rash typically appears on the **3rd day** of illness. Unlike measles, the rash is centrifugal (more dense on extremities) and progresses synchronously from papules to umbilicated vesicles and pustules. * **Chickenpox (Varicella):** The rash appears very early, usually on the **1st day** of fever. It is pleomorphic (all stages of rash—vesicles, papules, crusts—seen simultaneously) and has a centripetal distribution (more on the trunk). **High-Yield Clinical Pearls for NEET-PG:** * **Koplik Spots:** Pathognomonic for measles; small white spots on an erythematous base found on the buccal mucosa opposite the lower 2nd molars (appears 1–2 days before the rash). * **Vitamin A:** Supplementation is mandatory in measles management to reduce morbidity and mortality (especially blindness and pneumonia). * **Infectivity:** Patients are infectious from 4 days before to 4 days after the appearance of the rash. * **SSPE:** Subacute Sclerosing Panencephalitis is a rare, delayed neurological complication occurring years after the initial infection.

Q: What is the time gap between the appearance of Koplik's spots and the cutaneous rash in measles?

3-4 days. **Explanation:** Measles (Rubeola) follows a distinct chronological progression of clinical features. The correct answer is **3-4 days** because of the specific timing of the prodromal and eruptive phases. 1. **Why Option B is correct:** Measles has a prodromal stage characterized by the "3 Cs" (Cough, Coryza, Conjunctivitis) and fever. **Koplik’s spots**—the pathognomonic enanthem—typically appear on the buccal mucosa opposite the lower second molars about **2 days before** the rash. The characteristic maculopapular rash (exanthem) usually appears on the **4th day** of the fever. Therefore, the interval between the appearance of Koplik’s spots and the cutaneous rash is approximately **2 to 4 days** (averaging 3-4 days). 2. **Why other options are incorrect:** * **Option A (24 hours):** This is too short; Koplik's spots usually precede the rash by at least 48 hours. * **Option C (2 weeks):** This is the approximate incubation period of Measles (10–14 days), not the interval between clinical signs. * **Option D (10 days):** This is the time from exposure to the onset of the first symptom (fever), not the gap between the spots and the rash. **High-Yield Clinical Pearls for NEET-PG:** * **Koplik’s Spots:** Described as "grains of salt on a red background." They disappear within 24–48 hours after the rash appears. * **Rash Progression:** Starts behind the ears (retro-auricular), spreads to the face/neck, then downwards to the trunk and limbs (cephalocaudal progression). * **Infectivity:** A patient is infectious from **4 days before to 4 days after** the appearance of the rash. * **Vitamin A:** Supplementation is recommended for all children with measles to prevent complications like blindness and pneumonia.

Q: Which among the following is the commonest complication of meningitis?

Seizure. **Explanation:** Acute bacterial meningitis is a medical emergency in pediatrics, and understanding its complications is high-yield for NEET-PG. **Why Seizure is the Correct Answer:** Seizures are the **most common acute complication** of meningitis, occurring in approximately **20–30%** of patients. They typically occur within the first 48–72 hours of illness. The underlying pathophysiology involves cortical irritation caused by meningeal inflammation, cerebral edema, focal ischemia (due to vasculitis), or metabolic derangements (like hyponatremia due to SIADH). **Analysis of Incorrect Options:** * **Deafness (Sensorineural Hearing Loss):** This is the **most common permanent/long-term neurological sequela** (occurring in ~10% of survivors), particularly with *S. pneumoniae*. However, it is less frequent than acute seizures. * **Brain Abscess:** This is a rare complication of meningitis. It is more commonly associated with specific organisms like *Citrobacter koseri* or *Proteus* in neonates. * **Hydrocephalus:** This is a known complication (usually communicating type due to impaired CSF absorption), but its incidence is lower than that of seizures. **NEET-PG High-Yield Pearls:** * **Most common sequela overall:** Seizures (Acute phase). * **Most common permanent sequela:** Hearing loss (Perform BERA/Audiometry for all survivors before discharge). * **Most common cause of meningitis (overall):** *Streptococcus pneumoniae*. * **Most common cause in neonates:** Group B Streptococcus (GBS), followed by *E. coli*. * **Subdural effusion:** Common in infants (especially with *H. influenzae*); suspect if there is persistent fever or bulging fontanelle despite 48-72 hours of antibiotics.

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.

Question 1

A patient presents with fever, cough, and headache. On the fourth day of illness, a rash develops. What is the probable diagnosis?

Accepted Answer

Measles

Answer

Mumps

Answer

Smallpox

Answer

Chickenpox

Question 2

What is the time gap between the appearance of Koplik's spots and the cutaneous rash in measles?

Accepted Answer

3-4 days

Answer

24 hours

Answer

2 weeks

Answer

10 days

Question 3

Which among the following is the commonest complication of meningitis?

Accepted Answer

Seizure

Answer

Deafness

Answer

Brain abscess

Answer

Hydrocephalus

Question 4

What is this teeth abnormality?

Accepted Answer

Hutchinson's teeth

Answer

Mulberry molars

Answer

Natal teeth

Answer

Supernumerary teeth

Question 5

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 6

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 7

What is the drug of choice for pertussis in children?

Accepted Answer

Azithromycin

Answer

Penicillin

Answer

Erythromycin

Answer

Ampicillin

Question 8

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 9

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 10

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

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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