Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 331: Which of the following is NOT a criterion for diagnosing Systemic Inflammatory Response Syndrome (SIRS)?

A. Temperature > 38.5°C or < 36°C
B. Respiratory rate > 2 standard deviations above normal for age
C. In infants < 1 year, persistent bradycardia over 0.5 hour
D. More than 50% immature neutrophils (Correct Answer)

Explanation: To diagnose **Systemic Inflammatory Response Syndrome (SIRS)** in the pediatric population, specific clinical and laboratory criteria must be met. According to the International Pediatric Sepsis Consensus Conference, SIRS requires the presence of at least **two** of the four criteria, one of which **must** be abnormal temperature or leukocyte count. ### Why Option D is the Correct Answer Option D is incorrect because the threshold for immature neutrophils (bands) is **>10%**, not >50%. While an elevated immature-to-total neutrophil ratio is a hallmark of the inflammatory response, a 50% cutoff is clinically extreme and not part of the diagnostic criteria. ### Explanation of Other Options (SIRS Criteria) * **Option A (Temperature):** Core temperature of **>38.5°C or <36°C** is a primary criterion. * **Option B (Respiratory Rate):** Mean respiratory rate **>2 standard deviations (SD) above normal** for age or the need for mechanical ventilation (not related to underlying neuromuscular disease) is a valid criterion. * **Option C (Heart Rate):** Tachycardia is standard, but in **infants <1 year**, persistent **bradycardia** (mean HR <10th percentile for age) for >0.5 hours is a specific and recognized criterion. ### NEET-PG High-Yield Pearls * **Mandatory Requirement:** Unlike adults, pediatric SIRS **cannot** be diagnosed without either an abnormal temperature or an abnormal white blood cell count. * **WBC Criterion:** Leukocyte count elevated or depressed for age (not secondary to chemotherapy) OR **>10% immature neutrophils**. * **Sepsis Definition:** Sepsis is defined as **SIRS + suspected or proven infection**. * **Severe Sepsis:** Sepsis plus cardiovascular dysfunction, ARDS, or two or more other organ dysfunctions.

Question 332: A 27-year-old man develops bilateral parotid gland swelling and orchitis, and is generally ill with fever of 102°F. Which of the following substances is most likely to be significantly elevated in the patient's serum?

A. Alanine aminotransferase (ALT)
B. Amylase (Correct Answer)
C. Aspartate aminotransferase (AST)
D. Ceruloplasmin

Explanation: ### Explanation The clinical presentation of bilateral parotid swelling, fever, and orchitis in a young male is classic for **Mumps**, a viral infection caused by the *Rubulavirus* (Paramyxoviridae family). **Why Amylase is the Correct Answer:** Serum amylase is significantly elevated in mumps due to involvement of the **salivary glands** (parotitis). While amylase is commonly associated with the pancreas, it is also produced by the salivary glands (S-type isoenzyme). In mumps, inflammation and damage to the parotid acinar cells lead to the leakage of amylase into the bloodstream. Additionally, if the patient develops **mumps pancreatitis** (a known complication), the pancreatic isoenzyme (P-type) will also contribute to the elevation. **Why Other Options are Incorrect:** * **ALT and AST (Options A & C):** These are markers of hepatocellular injury. While some viral infections cause hepatitis, mumps typically spares the liver. Therefore, transaminases remain within normal limits. * **Ceruloplasmin (Option D):** This is a copper-binding protein and an acute-phase reactant. While it might rise slightly during general inflammation, it is not a specific or significant marker for mumps. It is primarily used in the diagnosis of Wilson’s disease. **NEET-PG High-Yield Pearls:** * **Most common complication in children:** Aseptic meningitis. * **Most common complication in post-pubertal males:** Unilateral Orchitis (can lead to testicular atrophy, but rarely causes infertility). * **Most common cause of sensorineural hearing loss in children:** Mumps (typically unilateral and permanent). * **Diagnosis:** Primarily clinical; confirmed by IgM antibodies or PCR from oral swabs/urine. * **Prevention:** Live attenuated vaccine (Jeryl Lynn strain is most common).

Question 333: A 3-year-old child presents with weakness and a hemoglobin level of <5 gm/100 ml. There is a history of joint swelling and bleeding spots. What is the most likely causative organism?

A. Hookworm (Correct Answer)
B. Roundworm
C. Whipworm
D. Pinworm

Explanation: **Explanation:** The clinical presentation of severe anemia (Hb <5 gm/dl) in a child, coupled with signs of nutritional deficiency and potential occult blood loss, points toward **Hookworm infestation** (*Ancylostoma duodenale* or *Necator americanus*). **Why Hookworm is correct:** Hookworms are the most common helminthic cause of **iron deficiency anemia**. They attach to the small intestinal mucosa using buccal capsules (teeth or cutting plates) and suck host blood. A single *A. duodenale* can cause up to 0.2 ml of blood loss per day. Chronic infection leads to profound microcytic hypochromic anemia, which can manifest as weakness, pallor, and in severe cases, congestive heart failure. The "joint swelling and bleeding spots" mentioned in the history often refer to the associated malnutrition and potential Vitamin C/K deficiencies secondary to malabsorption or chronic illness. **Why other options are incorrect:** * **Roundworm (*Ascaris lumbricoides*):** Primarily causes intestinal obstruction, Loeffler’s syndrome (pneumonitis), or biliary colic. It does not cause significant blood loss. * **Whipworm (*Trichuris trichiura*):** While heavy infections can cause "Trichuris dysentery syndrome" and rectal prolapse, the degree of anemia is significantly less than that seen in hookworm. * **Pinworm (*Enterobius vermicularis*):** Causes perianal pruritus (worse at night) but does not cause anemia or systemic bleeding. **NEET-PG High-Yield Pearls:** * **Route of entry:** Filariform larvae penetrate intact skin (usually feet), leading to **Ground Itch**. * **Diagnosis:** Presence of non-bile stained, oval, segmented eggs in stool. * **Treatment of choice:** Albendazole (400 mg single dose) or Mebendazole. * **Public Health:** Hookworm is a major cause of "Anemic Heart Failure" in tropical pediatric populations.

Question 334: Aspirin is associated with which of the following conditions?

A. Reye's syndrome (Correct Answer)
B. Sjogren's syndrome
C. Reiter's syndrome
D. None of the above

Explanation: **Explanation:** **Reye’s Syndrome (Correct Answer):** Reye’s syndrome is a rare but life-threatening condition characterized by **acute encephalopathy** and **fatty degeneration of the liver (microvesicular steatosis)**. It is strongly associated with the use of **aspirin (salicylates)** in children and adolescents during a viral prodrome, most commonly **Influenza B** or **Varicella**. The underlying mechanism involves mitochondrial injury, leading to impaired fatty acid oxidation and hyperammonemia. Due to this risk, aspirin is contraindicated in children under 16 years of age, except in specific conditions like Kawasaki disease. **Incorrect Options:** * **Sjogren’s syndrome:** This is a chronic autoimmune disorder characterized by lymphocytic infiltration of exocrine glands, leading to dry eyes (xerophthalmia) and dry mouth (xerostomia). It is not triggered by salicylate use. * **Reiter’s syndrome (Reactive Arthritis):** This is a triad of arthritis, urethritis, and conjunctivitis ("can't see, can't pee, can't climb a tree") that typically follows a gastrointestinal or genitourinary infection (e.g., Chlamydia, Salmonella). It is an HLA-B27 associated spondyloarthropathy. **High-Yield Clinical Pearls for NEET-PG:** * **Biopsy Finding:** Liver biopsy in Reye’s syndrome shows **microvesicular steatosis** (no inflammation). * **Biochemical Markers:** Elevated serum ammonia, prolonged Prothrombin Time (PT), and elevated AST/ALT with **normal bilirubin**. * **Management:** Supportive care; focus on reducing cerebral edema (Mannitol) and managing hyperammonemia. * **Exception:** Aspirin is the drug of choice in **Kawasaki Disease**, despite the risk of Reye's syndrome; however, these patients must receive the influenza vaccine.

Question 335: Stool investigation of a child who presented with anemia revealed worm infestation. Which of the following worm infestations is associated with iron deficiency anemia?

A. Whipworm
B. Hookworm (Correct Answer)
C. Roundworm
D. Pinworm

Explanation: **Explanation:** **Hookworm** (*Ancylostoma duodenale* and *Necator americanus*) is the classic cause of **Iron Deficiency Anemia (IDA)** in children. The worms attach to the small intestinal mucosa using buccal capsules (teeth or cutting plates) and suck host blood. They also secrete anticoagulants (factor Xa inhibitors), leading to persistent bleeding from attachment sites. A single *A. duodenale* can cause up to 0.2 mL of blood loss per day. Chronic infestation leads to a depletion of iron stores, resulting in microcytic hypochromic anemia. **Analysis of Incorrect Options:** * **Whipworm (*Trichuris trichiura*):** While heavy infestations can cause "Trichuris Dysentery Syndrome" and rectal prolapse, the primary hematological concern is chronic blood loss from the colon, which is generally less severe than hookworm-induced IDA. * **Roundworm (*Ascaris lumbricoides*):** These do not attach to the mucosa or suck blood. They primarily cause malnutrition by competing for nutrients or intestinal obstruction (bolus formation). * **Pinworm (*Enterobius vermicularis*):** These reside in the cecum and appendix. Their hallmark symptom is perianal pruritus; they do not cause blood loss or anemia. **Clinical Pearls for NEET-PG:** * **Route of Entry:** Filariform larvae penetrate intact skin (usually feet), often causing **Ground Itch**. * **Loeffler’s Syndrome:** Transient eosinophilic pneumonia occurring during the pulmonary migration phase of *Ascaris* or Hookworms. * **Diagnosis:** Presence of non-bile stained, oval, segmented eggs in stool. * **Treatment:** Albendazole (400 mg single dose) is the drug of choice for mass deworming.

Question 336: Which of the following organisms is most commonly responsible for Sudden Infant Death Syndrome (SIDS), particularly after honey consumption by the infant?

A. Clostridium botulinum (Correct Answer)
B. Staphylococcus aureus
C. E. coli
D. Clostridium perfringens

Explanation: **Explanation:** **Clostridium botulinum** is the correct answer because it is the causative agent of **Infant Botulism**. In infants under 12 months, the intestinal flora is not fully developed, allowing ingested *C. botulinum* spores to germinate, colonize the gut, and release a potent neurotoxin. **Honey** is a well-known environmental reservoir for these spores. The toxin inhibits acetylcholine release at the neuromuscular junction, leading to "Floppy Baby Syndrome" (descending paralysis). In severe cases, it causes sudden respiratory failure, which is a recognized, preventable cause of **Sudden Infant Death Syndrome (SIDS)**. **Analysis of Incorrect Options:** * **Staphylococcus aureus:** While a common cause of skin infections and food poisoning (via preformed enterotoxin), it is not linked to honey consumption or the specific pathogenesis of SIDS. * **E. coli:** Primarily associated with neonatal sepsis, meningitis, or gastroenteritis, but not with the toxidrome leading to SIDS following honey ingestion. * **Clostridium perfringens:** Causes gas gangrene and food poisoning in adults; it does not colonize the infant gut to cause the paralytic syndrome seen in botulism. **Clinical Pearls for NEET-PG:** * **Age Group:** Most common between **2 to 6 months**. * **Classic Presentation:** Constipation (earliest sign), followed by weak cry, poor suck reflex, loss of head control, and generalized hypotonia (**"Floppy Baby"**). * **Diagnosis:** Identification of spores or toxin in the **stool** (not the serum, as toxin levels are often too low to detect). * **Management:** Treatment is with **Botulism Immune Globulin Intravenous (BIG-IV)**. Avoid honey in all infants <1 year of age.

Question 337: The shake test shown below can be done to know:

A. Whether the vaccine was exposed to heat
B. Whether the vaccine had been frozen at some point of time in the cold chain (Correct Answer)
C. Whether the expiry date of the vaccine has been reached
D. Whether the vaccine needs to be mixed with normal saline

Explanation: ***Whether the vaccine had been frozen at some point of time in the cold chain*** - The shake test is a **WHO cold chain quality test** specifically designed to detect **freeze-damaged adsorbed vaccines** like DPT, TT, and Hepatitis B. - When vaccines containing **aluminum adjuvants** are frozen, the adjuvant particles clump together and settle faster after shaking, indicating **cold chain failure**. *Whether the vaccine was exposed to heat* - Heat exposure does **not affect the sedimentation rate** of aluminum adjuvants after shaking, making the shake test ineffective for heat detection. - Heat damage requires **vaccine vial monitors (VVMs)** or temperature monitoring devices, not physical shake tests. *Whether the expiry date of the vaccine has been reached* - Expiry dates are determined by **time-based stability studies** and are clearly printed on vaccine labels. - The shake test assesses **physical integrity** of adjuvants, not time-dependent potency loss or expiration status. *Whether the vaccine needs to be mixed with normal saline* - Mixing requirements are determined by **vaccine formulation** and manufacturer instructions, not physical appearance after shaking. - The shake test compares **sedimentation rates** between test and control vials to detect freeze damage, not mixing needs.

Question 338: What is the most common cause of acute aseptic meningitis in children?

A. Arbovirus
B. Respiratory syncytial virus
C. Enterovirus (Correct Answer)
D. Herpes family

Explanation: **Explanation:** **Enteroviruses** (specifically Coxsackievirus A and B, and Echoviruses) are the most common cause of acute aseptic meningitis in children, accounting for **>80-90% of cases** where a pathogen is identified. They typically follow a seasonal pattern, peaking in late summer and early autumn. The virus enters via the fecal-oral or respiratory route, replicates in the lymphoid tissue of the GI tract, and spreads hematogenously to the central nervous system. **Analysis of Incorrect Options:** * **Arboviruses (Option A):** While significant causes of meningoencephalitis (e.g., Japanese Encephalitis in specific endemic regions), they are less common overall than Enteroviruses and often present with more severe parenchymal involvement (encephalitis). * **Respiratory Syncytial Virus (Option B):** RSV is a primary cause of lower respiratory tract infections (bronchiolitis and pneumonia) in infants. It rarely involves the CNS. * **Herpes Family (Option D):** HSV-2 is a common cause of aseptic meningitis in adults, and HSV-1 is the leading cause of sporadic fatal encephalitis. While they cause CNS infections in neonates and children, they do not match the high prevalence of Enteroviruses. **High-Yield Clinical Pearls for NEET-PG:** * **CSF Findings in Aseptic Meningitis:** Normal glucose, normal to slightly elevated protein, and lymphocytic pleocytosis (though neutrophils may predominate in the first 24 hours). * **Diagnosis:** PCR of the CSF is the gold standard for Enteroviral meningitis due to its high sensitivity. * **Prognosis:** Generally excellent with supportive care, unlike bacterial meningitis. * **Hand-Foot-Mouth Disease:** Often co-exists or precedes meningitis caused by Coxsackievirus A16 or Enterovirus 71.

Question 339: What is the antibiotic of choice for pertussis?

A. Ampicillin
B. Gentamicin
C. Erythromycin (Correct Answer)
D. Penicillin

Explanation: **Explanation:** **Correct Option: C (Erythromycin)** Pertussis, or "Whooping Cough," is caused by the Gram-negative coccobacillus *Bordetella pertussis*. **Macrolides** are the treatment of choice because they effectively inhibit protein synthesis of the bacteria, thereby reducing the period of communicability. While **Erythromycin** (50 mg/kg/day for 14 days) is the classic textbook answer, newer macrolides like **Azithromycin** (preferred in infants <1 month due to lower risk of infantile hypertrophic pyloric stenosis) and **Clarithromycin** are now frequently used in clinical practice due to better tolerability. **Why other options are incorrect:** * **A & D (Ampicillin/Penicillin):** *B. pertussis* is inherently resistant to most penicillins. These drugs do not achieve adequate inhibitory concentrations against the organism and are ineffective in shortening the clinical course or reducing transmission. * **B (Gentamicin):** Aminoglycosides like Gentamicin are primarily used for systemic aerobic Gram-negative infections (e.g., *E. coli*, *Pseudomonas*) but have no clinical role in treating pertussis. **High-Yield Clinical Pearls for NEET-PG:** * **Best time to treat:** Antibiotics are most effective during the **Catarrhal stage**. Once the **Paroxysmal stage** begins, antibiotics do not alter the clinical course but are still given to limit the spread to others. * **Post-Exposure Prophylaxis (PEP):** Macrolides are recommended for all household contacts, regardless of vaccination status. * **Drug of Choice for Macrolide-allergic patients:** Trimethoprim-Sulfamethoxazole (TMP-SMX). * **Diagnosis:** The gold standard is **Culture** (Regan-Lowe or Bordet-Gengou medium), but **PCR** is the most sensitive rapid test.

Question 340: A mother diagnosed with chickenpox delivered a healthy, afebrile, term infant 7 days ago. What is the most appropriate management step for the infant?

A. Advise the mother to continue regular baby care (Correct Answer)
B. Hospitalize the infant in an isolation ward
C. Administer acyclovir to the infant
D. Administer varicella-zoster immunoglobulin (VZIG) to the infant

Explanation: **Explanation:** The management of neonatal varicella depends entirely on the **timing of maternal infection** relative to delivery. **1. Why Option A is Correct:** In this case, the mother developed chickenpox **7 days before delivery**. This timeline allows sufficient time (usually >5 days) for the mother to produce IgG antibodies and transfer them across the placenta to the fetus. These maternal antibodies provide passive immunity, protecting the infant from severe disseminated disease. Therefore, the infant is not at high risk for "progressive neonatal varicella," and the mother can continue regular baby care, including breastfeeding (provided no active lesions are on the nipples). **2. Why the Other Options are Incorrect:** * **Option D (VZIG):** VZIG is indicated only if the maternal onset of rash occurs **5 days before to 2 days after delivery**. In this "danger window," the infant is exposed to the virus during birth but does not receive protective maternal antibodies. Since this mother’s rash started 7 days ago, VZIG is not required. * **Option C (Acyclovir):** Acyclovir is reserved for infants who show clinical signs of varicella or for high-risk infants where VZIG was indicated but unavailable. It is not used for prophylaxis in an asymptomatic infant with maternal antibody protection. * **Option B (Isolation):** While the mother should practice hand hygiene, the infant has already been exposed in utero and is protected by maternal antibodies; hospitalization is unnecessary for a healthy, term infant. **Clinical Pearls for NEET-PG:** * **The "5-2" Rule:** VZIG is mandatory if maternal rash appears **5 days before to 2 days after** delivery. * **Congenital Varicella Syndrome:** Occurs if maternal infection happens in the **first 20 weeks** of gestation (characterized by cicatricial skin scars, limb hypoplasia, and microcephaly). * **Breastfeeding:** Is NOT contraindicated in maternal chickenpox unless active lesions are present on the breast.

Practice by Chapter

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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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