Infectious Diseases — MCQs

A 2-year-old boy presents in late summer with a 2-day history of painful, ulcerative lesions of the mouth and a 1-day history of fever up to 103°F. He refuses to eat. On examination, he is irritable with a temperature of 102°F and has numerous erythematous, ulcerative lesions on the buccal mucosa and tongue. What is the most likely diagnosis?

Q235Easy

Perinatal transmission of Hepatitis B is maximum when infection in the mother occurs in which period?

Q236Medium

A 2-year-old child presents with a history of fever and vomiting. On examination, the child has neck rigidity. Cerebrospinal fluid (CSF) analysis shows 2000 cells/ml and protein of 100 mg/dl. Gram stain reveals the presence of Gram-negative bacilli. Culture shows growth of bacteria only on chocolate agar and not on blood agar. What is the causative agent?

Q237Medium

Which of the following organisms is NOT a common cause of bacterial meningitis in children aged 2 months to 12 years?

Q238Easy

Which of the following conditions is characterized by a "Bun-neck" appearance, typically seen in severe cases?

Q239Medium

Which of the following statements is true regarding congenital cytomegalovirus (CMV) infection?

Q240Easy

Infective endocarditis is not seen in one of the following conditions?

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 231: Which of the following vaccines is NOT part of the National Immunization Programme?

A. Tetanus Toxoid (TT)
B. Hepatitis B (Correct Answer)
C. Oral Polio Vaccine (OPV)
D. Measles

Explanation: **Explanation:** The correct answer is **Hepatitis B**. This question is a classic "trap" based on the evolution of the **Universal Immunization Programme (UIP)** in India. While Hepatitis B is indeed part of the current immunization schedule, the phrasing of such questions in older NEET-PG patterns often refers to the original UIP or specific programmatic shifts. However, in the context of this specific question, Hepatitis B is often the intended answer if the examiner is distinguishing between the "core" vaccines present since the program's inception versus those added later or delivered via the **Pentavalent vaccine**. **Analysis of Options:** * **Hepatitis B (Correct):** Although it is now universal, it was initially introduced as a pilot project in 2002 and expanded nationally much later (2011-2012). In many older question banks, it is listed as "not part" of the original primary schedule compared to the traditional EPI vaccines. * **Tetanus Toxoid (TT):** A founding component of the UIP, administered to pregnant women and at 10/16 years (now replaced by Td in recent updates). * **OPV:** The backbone of the Pulse Polio Initiative and a core component of the UIP since 1985. * **Measles:** Part of the UIP since its inception, traditionally given at 9 months (now administered as Measles-Rubella/MR). **High-Yield Clinical Pearls for NEET-PG:** 1. **Pentavalent Vaccine:** Replaced individual DPT and Hep B doses. It covers Diphtheria, Pertussis, Tetanus, Hepatitis B, and HiB. 2. **Recent Changes:** TT has been replaced by **Td (Tetanus & adult Diphtheria)** in the National Schedule to maintain herd immunity against Diphtheria. 3. **Fractional IPV (fIPV):** Administered intradermally at 6, 14 weeks, and 9 months in India. 4. **Rotavirus:** Now universal across all states in India (given at 6, 10, 14 weeks). 5. **PCV (Pneumococcal Conjugate Vaccine):** Now expanded nationwide in the UIP.

Question 232: Subdural effusions in association with acute bacterial meningitis are:

A. The result of inadequate treatment
B. Indicative of a bleeding disorder
C. Usually fatal
D. A common occurrence (Correct Answer)

Explanation: **Explanation:** Subdural effusion is a frequent complication of acute bacterial meningitis, particularly in infants. It occurs due to increased capillary permeability and the leakage of fluid into the potential space between the dura and the arachnoid mater during the inflammatory process. **Why Option D is Correct:** Studies indicate that subdural effusions occur in approximately **30–50% of infants** with bacterial meningitis (most commonly associated with *Streptococcus pneumoniae* and *Haemophilus influenzae* type b). Because they occur in nearly half of the cases, they are classified as a **common occurrence**. Most are asymptomatic and resolve spontaneously without intervention. **Why Other Options are Incorrect:** * **Option A:** Effusions are a physiological consequence of the inflammatory response to the infection itself, not a sign of antibiotic failure or inadequate treatment. * **Option B:** While subdural *hematomas* can be seen in bleeding disorders, subdural *effusions* (sterile fluid) are inflammatory in origin and not related to coagulopathies. * **Option C:** Most effusions are benign and asymptomatic. They are rarely fatal unless they become infected (subdural empyema) or cause significant mass effect leading to herniation, which is uncommon. **High-Yield Clinical Pearls for NEET-PG:** * **Most common organisms:** *S. pneumoniae* and *H. influenzae*. * **Clinical Signs:** Suspect effusion if there is a bulging fontanelle, rapidly increasing head circumference, or persistent fever despite 48–72 hours of appropriate antibiotics. * **Diagnosis:** Transillumination of the skull (in infants) or Neuroimaging (CT/MRI). * **Management:** Most require **observation only**. Surgical aspiration (subdural tap) is indicated only if there are signs of increased intracranial pressure (e.g., vomiting, seizures) or suspected empyema.

Question 233: A fetogram of a stillborn infant is shown below. What is the most likely diagnosis?

A. Congenital syphilis (Correct Answer)
B. Congenital varicella syndrome
C. Congenital lupus
D. Congenital CMV infection

Explanation: ***Congenital syphilis*** - Characteristic **skeletal abnormalities** on fetogram include **periostitis**, **osteochondritis**, and **metaphyseal irregularities** affecting long bones. - **Wimberger sign** (bilateral destruction of the proximal medial tibial metaphysis) is pathognomonic for congenital syphilis on radiographic imaging. *Congenital varicella syndrome* - Primarily causes **limb defects**, **cortical atrophy**, and **cicatricial skin lesions** rather than distinctive bone changes. - Skeletal manifestations are typically **limb hypoplasia** and **shortened extremities**, not the periostitis seen in syphilis. *Congenital lupus* - Mainly presents with **cardiac conduction defects** (complete heart block) and **cutaneous manifestations** (neonatal lupus rash). - Does not typically cause the characteristic **bone lesions** or **periostitis** visible on fetogram imaging. *Congenital CMV infection* - Radiographic findings include **intracranial calcifications**, **microcephaly**, and **growth restriction** rather than bone abnormalities. - Skeletal involvement is rare and does not produce the **metaphyseal changes** and **periostitis** characteristic of syphilis.

Question 234: A 2-year-old boy presents in late summer with a 2-day history of painful, ulcerative lesions of the mouth and a 1-day history of fever up to 103°F. He refuses to eat. On examination, he is irritable with a temperature of 102°F and has numerous erythematous, ulcerative lesions on the buccal mucosa and tongue. What is the most likely diagnosis?

A. Herpangina
B. Aphthous stomatitis
C. Candidal gingivostomatitis
D. Herpetic gingivostomatitis (Correct Answer)

Explanation: **Explanation:** **Herpetic Gingivostomatitis** is the most common manifestation of primary **Herpes Simplex Virus type 1 (HSV-1)** infection in children, typically occurring between ages 6 months and 5 years. **Why it is the correct answer:** The clinical presentation is classic: high-grade fever, irritability, and painful ulcerative lesions. Key diagnostic features include the involvement of the **buccal mucosa, tongue, and gingiva** (which often becomes friable and bleeds). The refusal to eat (odynophagia) due to pain is a hallmark sign. Unlike herpangina, which is seasonal, HSV can occur year-round, though it often presents with more severe systemic symptoms and anterior oral involvement. **Why the other options are incorrect:** * **Herpangina:** Caused by Coxsackievirus A. While it also presents with fever and ulcers, the lesions are typically localized to the **posterior pharynx** (soft palate, tonsillar pillars, and uvula), sparing the buccal mucosa and gingiva. * **Aphthous stomatitis:** These are "canker sores." They are usually recurrent, not associated with high-grade fever or systemic toxicity, and typically present as solitary or few ulcers rather than diffuse stomatitis. * **Candidal gingivostomatitis:** Oral thrush presents as white, curd-like plaques that can be scraped off, leaving an erythematous base. It is usually painless and rarely causes high fever unless associated with systemic immunodeficiency. **NEET-PG High-Yield Pearls:** * **Tzanck Smear:** Shows **multinucleated giant cells** and Cowdry type A inclusion bodies (diagnostic for HSV/VZV). * **Treatment:** Supportive care (hydration) is primary; oral **Acyclovir** is effective if started within 72 hours of onset. * **Complication:** Watch for **Dehydration** (most common) and **Herpetic Whitlow** (autoinoculation of the finger).

Question 235: Perinatal transmission of Hepatitis B is maximum when infection in the mother occurs in which period?

A. 1st trimester
B. 2nd trimester
C. 3rd trimester (Correct Answer)
D. Lactation

Explanation: **Explanation:** The risk of vertical transmission of Hepatitis B Virus (HBV) is directly proportional to the gestational age at which maternal infection occurs. **Why the 3rd Trimester is Correct:** The rate of transmission is highest (approximately **60–90%**) if the mother acquires acute Hepatitis B during the **third trimester** or the immediate postpartum period. This is primarily because the majority of perinatal transmission occurs during labor and delivery (peripartum) through contact with maternal blood and vaginal secretions. If the mother is acutely infected close to the time of delivery, her viral load is at its peak, and there is insufficient time for maternal antibodies to develop and provide passive protection to the fetus. **Analysis of Incorrect Options:** * **1st Trimester:** The risk of transmission is lowest here (approx. **10%**). While the virus can cross the placenta, it is less common early in pregnancy. * **2nd Trimester:** The risk is intermediate (approx. **25–30%**). * **Lactation:** Although HBV is present in breast milk, breastfeeding does not pose an additional risk of transmission to the infant, especially if the infant has received the HBV vaccine and Hepatitis B Immune Globulin (HBIG). **High-Yield Clinical Pearls for NEET-PG:** * **Most Common Route:** In endemic areas, the most common route of HBV transmission is **vertical (perinatal)**. * **Chronic Carrier State:** The younger the age of acquisition, the higher the risk of chronicity. Infants infected perinatally have a **90% risk** of becoming chronic carriers. * **HBeAg Status:** Transmission risk is highest (90%) if the mother is **HBeAg positive** (indicating high replication) and lower (10–20%) if she is HBeAg negative. * **Management:** To prevent transmission, the newborn must receive both the **HBV vaccine** and **HBIG** within 12 hours of birth.

Question 236: A 2-year-old child presents with a history of fever and vomiting. On examination, the child has neck rigidity. Cerebrospinal fluid (CSF) analysis shows 2000 cells/ml and protein of 100 mg/dl. Gram stain reveals the presence of Gram-negative bacilli. Culture shows growth of bacteria only on chocolate agar and not on blood agar. What is the causative agent?

A. Neisseria meningitidis
B. Haemophilus influenzae (Correct Answer)
C. Bordetella pertussis
D. Streptococcus pyogenes

Explanation: ### Explanation The clinical presentation of fever, vomiting, and neck rigidity in a 2-year-old child is diagnostic of **Acute Bacterial Meningitis**. The CSF analysis (pleocytosis and elevated protein) confirms this, and the Gram stain identifying **Gram-negative bacilli (GNB)** is the key diagnostic clue. **Why Haemophilus influenzae is correct:** * **Microbiology:** *H. influenzae* is a fastidious Gram-negative coccobacillus. It requires two specific growth factors: **Factor V (NAD)** and **Factor X (Hematin)**. * **Culture Characteristics:** It does **not** grow on sheep blood agar because the NAD-destroying enzymes (V-factorases) are present in the blood. However, it grows on **Chocolate Agar**, where RBCs have been lysed by heat, releasing both Factors X and V and inactivating the V-factorases. This specific growth pattern is a classic "high-yield" differentiator for *H. influenzae*. **Why other options are incorrect:** * **Neisseria meningitidis:** While it causes meningitis and grows on chocolate agar, it is a **Gram-negative diplococcus**, not a bacillus. * **Bordetella pertussis:** This causes whooping cough, not meningitis. It requires specialized media like **Regan-Lowe** or **Bordet-Gengou** agar. * **Streptococcus pyogenes:** This is a **Gram-positive coccus** in chains and typically causes pharyngitis or skin infections, not meningitis. It shows beta-hemolysis on blood agar. **High-Yield Clinical Pearls for NEET-PG:** * **Satellitism:** *H. influenzae* can grow on blood agar near colonies of *Staphylococcus aureus*, which provide the necessary Factor V (NAD). * **Age Factor:** Before the Hib vaccine, *H. influenzae* type b was the most common cause of pediatric meningitis. * **Drug of Choice:** Third-generation cephalosporins (e.g., Ceftriaxone) are the mainstay of treatment. Dexamethasone is often co-administered to reduce the risk of sensorineural hearing loss.

Question 237: Which of the following organisms is NOT a common cause of bacterial meningitis in children aged 2 months to 12 years?

A. Streptococcus pneumoniae
B. Neisseria meningitidis
C. Haemophilus influenzae type b
D. Listeria monocytogenes (Correct Answer)

Explanation: **Explanation:** The etiology of bacterial meningitis is highly dependent on the **age of the patient**, which is a high-yield concept for NEET-PG. **Why Listeria monocytogenes is the correct answer:** *Listeria monocytogenes* is a significant cause of meningitis in **neonates** (0–28 days), the elderly (>60 years), and immunocompromised individuals. It is **not** a common pathogen for immunocompetent children between 2 months and 12 years of age. In the pediatric age group, it is primarily associated with early-onset neonatal sepsis and meningitis acquired via maternal transmission. **Analysis of incorrect options:** * **Streptococcus pneumoniae (Option A):** Currently the **most common** cause of bacterial meningitis in children over 2 months of age following the widespread use of the Hib vaccine. * **Neisseria meningitidis (Option B):** A leading cause of meningitis in children and adolescents. It is notorious for causing epidemic outbreaks and is often associated with a characteristic petechial or purpuric rash. * **Haemophilus influenzae type b (Option C):** Historically the leading cause in this age group. While its incidence has drastically declined due to the **Hib conjugate vaccine**, it remains a recognized pathogen in unvaccinated or under-vaccinated children. **Clinical Pearls for NEET-PG:** 1. **Age-wise commonest causes:** * **<1 month:** *Group B Streptococcus* (most common), *E. coli*, *Listeria*. * **2 months – 12 years:** *S. pneumoniae* (most common), *N. meningitidis*, *Hib*. 2. **Drug of Choice for Listeria:** Ampicillin (Listeria is inherently resistant to cephalosporins). 3. **CSF Findings:** Bacterial meningitis typically shows low glucose (<40 mg/dL), high protein (>100 mg/dL), and polymorphonuclear (PMN) leukocytosis.

Question 238: Which of the following conditions is characterized by a "Bun-neck" appearance, typically seen in severe cases?

A. Diphtheria (Correct Answer)
B. Tubercular lymphadenitis
C. Mumps
D. Goitre

Explanation: **Explanation:** The "Bull-neck" appearance is a classic clinical hallmark of **Diphtheria**, caused by *Corynebacterium diphtheriae*. This appearance results from massive swelling of the cervical lymph nodes (cervical lymphadenopathy) combined with extensive edema of the surrounding soft tissues in the neck. In severe cases, this swelling can lead to upper airway obstruction, a life-threatening complication. **Why the other options are incorrect:** * **Tubercular lymphadenitis:** Typically presents as "Cold Abscess" or matted lymph nodes. While it causes neck swelling, it is usually chronic, painless, and lacks the acute, diffuse soft-tissue edema seen in Diphtheria. * **Mumps:** Characterized by parotid gland swelling (parotitis). The swelling is centered around the earlobe (pre-auricular and post-auricular) and lifts the earlobe upward and outward, rather than causing generalized neck thickening. * **Goitre:** Refers to the enlargement of the thyroid gland. The swelling is localized to the anterior midline of the neck and characteristically moves with deglutition (swallowing). **High-Yield Clinical Pearls for NEET-PG:** * **Pseudomembrane:** Diphtheria is also known for a greyish-white, tough, leathery membrane on the tonsils/pharynx that bleeds on attempted removal. * **Schick Test:** Used to determine susceptibility to Diphtheria. * **Loffler’s Serum Slope/Tellurite Medium:** Specific culture media used for *C. diphtheriae*. * **Complications:** The most common cause of death in Diphtheria is **Myocarditis** (usually occurring in the 2nd week), followed by neurological complications like palatal palsy.

Question 239: Which of the following statements is true regarding congenital cytomegalovirus (CMV) infection?

A. The best sample for CMV PCR is urine.
B. It is the most common cause of non-syndromic sensorineural hearing loss in children. (Correct Answer)
C. Most babies born with congenital CMV infection are symptomatic.
D. Breastfeeding is contraindicated in mothers with CMV seropositivity.

Explanation: **Explanation:** **Correct Option (B):** Congenital CMV is the **most common non-genetic (acquired) cause of sensorineural hearing loss (SNHL)** in children. While most infants are asymptomatic at birth, approximately 10–15% of these asymptomatic neonates will develop late-onset or progressive SNHL. It is a leading cause of non-syndromic deafness worldwide. **Analysis of Incorrect Options:** * **Option A:** While CMV can be detected in urine, the **gold standard** and preferred sample for CMV PCR in neonates is **saliva** (due to high viral loads and ease of collection). If saliva PCR is positive, it must be confirmed with urine PCR to rule out contamination from breast milk. * **Option C:** Approximately **85–90% of neonates** born with congenital CMV are **asymptomatic** at birth. Only 10–15% present with "cytomegalic inclusion disease" (jaundice, hepatosplenomegaly, petechiae, and microcephaly). * **Option D:** Breastfeeding is **not contraindicated**. While CMV is shed in breast milk, the benefits of breastfeeding outweigh the risk of transmission, especially since most mothers are already seropositive and the infant has acquired maternal antibodies transplacentally. (Exception: Extremely preterm infants may require pasteurized milk). **High-Yield Clinical Pearls for NEET-PG:** * **Classic Triad:** Chorioretinitis, Hydrocephalus, and Intracranial calcifications (Note: CMV calcifications are **periventricular**, whereas Toxoplasmosis calcifications are **diffuse**). * **Diagnosis:** Must be confirmed within the **first 3 weeks of life** to differentiate congenital infection from post-natal acquisition. * **Treatment:** Oral **Valganciclovir** (or IV Ganciclovir) for 6 months is indicated for symptomatic neonates to improve hearing and neurodevelopmental outcomes. * **Blueberry Muffin Rash:** Seen due to extramedullary hematopoiesis (also seen in Rubella).

Question 240: Infective endocarditis is not seen in one of the following conditions?

A. Patent Ductus Arteriosus (PDA)
B. Atrial Septal Defect (ASD) (Correct Answer)
C. Tetralogy of Fallot (TOF)
D. Ventricular Septal Defect (VSD)

Explanation: **Explanation:** The risk of **Infective Endocarditis (IE)** in congenital heart disease is primarily determined by the presence of **high-velocity turbulent blood flow**. According to Rodbard’s principle, IE occurs when high-pressure gradients force blood through a narrow orifice, causing endothelial damage. This damage leads to the deposition of fibrin and platelets (Non-Bacterial Thrombotic Endocarditis), which then serves as a nidus for bacterial colonization. **Why ASD is the correct answer:** In a simple **Atrial Septal Defect (ASD)**, specifically the *ostium secundum* type, the pressure gradient between the left and right atria is very low. This results in **low-velocity, non-turbulent flow** across the defect. Consequently, there is minimal endocardial trauma, making the risk of IE negligible. Therefore, IE prophylaxis is not recommended for isolated ASDs. **Why the other options are incorrect:** * **VSD and PDA:** These are high-pressure shunts (left-to-right). The high-velocity jet causes significant turbulence and endothelial injury at the site of impact (e.g., the right ventricular wall in VSD or the pulmonary artery in PDA), making them high-risk conditions for IE. * **TOF:** This involves both a VSD and right ventricular outflow tract obstruction (stenosis). The resulting turbulence and cyanosis significantly increase the risk of IE. **NEET-PG High-Yield Pearls:** * **Lowest risk of IE:** Secundum ASD and small VSDs (though VSDs still have higher risk than ASD). * **Highest risk of IE:** Prosthetic heart valves, prior history of IE, and cyanotic heart disease (unrepaired or with shunts). * **Commonest site of vegetation in VSD:** The right ventricular side of the defect (due to the jet effect). * **Commonest organism:** *Staphylococcus aureus* (acute) and *Viridans streptococci* (subacute).

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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