Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 71: Which of the following signs and symptoms should arouse suspicion of streptococcal sore throat?

A. Exudates in the throat
B. Tender enlarged cervical lymph nodes
C. Absence of nasal and conjunctival injection
D. All of the above (Correct Answer)

Explanation: ### Explanation The diagnosis of **Group A Beta-Hemolytic Streptococcus (GABHS)** pharyngitis is primarily clinical, often guided by the **Centor Criteria** or the **McIsaac Score**. The goal is to differentiate bacterial infection from viral pharyngitis to ensure appropriate antibiotic stewardship. **Why "All of the above" is correct:** Streptococcal sore throat typically presents with an acute onset of symptoms that are localized to the oropharynx and lack the systemic "catarrhal" features of a viral upper respiratory infection. * **Exudates in the throat (Option A):** Patchy grayish-white tonsillar exudates are a classic sign of GABHS, though they can also be seen in Infectious Mononucleosis. * **Tender enlarged cervical lymph nodes (Option B):** Anterior cervical lymphadenopathy (specifically tender nodes) is a hallmark of bacterial pharyngitis. * **Absence of nasal and conjunctival injection (Option C):** This is a **crucial negative predictor**. The presence of cough, coryza (nasal congestion), conjunctivitis, or hoarseness strongly suggests a **viral etiology** (like Adenovirus or Rhinovirus) rather than Streptococcus. **High-Yield Clinical Pearls for NEET-PG:** 1. **Centor Criteria:** Points are given for: (1) Fever, (2) Tonsillar exudates, (3) Tender anterior cervical lymphadenopathy, and (4) **Absence of cough**. 2. **Age Factor:** GABHS is most common in children aged **5–15 years**. It is rare in children under 3 years. 3. **Scarlet Fever:** If a "sandpaper" rash and strawberry tongue accompany the sore throat, suspect Scarlet Fever (caused by erythrogenic toxins). 4. **Gold Standard Diagnosis:** Throat culture remains the gold standard, though Rapid Antigen Detection Tests (RADT) are used for immediate bedside screening. 5. **Treatment:** Penicillin V or Amoxicillin is the drug of choice to prevent **Acute Rheumatic Fever**.

Question 72: Which of the following is not a manifestation of neonatal tetanus?

A. Irritability
B. Hypotonia (Correct Answer)
C. Difficult feeding
D. Facial grimacing

Explanation: **Explanation:** Neonatal tetanus is caused by the toxin **tetanospasmin** produced by *Clostridium tetani*. The underlying pathophysiology involves the retrograde axonal transport of the toxin to the CNS, where it blocks the release of inhibitory neurotransmitters (GABA and glycine) from Renshaw cells. This results in **uncontrolled muscle spasms and hypertonia**, rather than hypotonia. * **Why Hypotonia is the correct answer:** In neonatal tetanus, the hallmark is **generalized muscle rigidity and spasms**. Hypotonia (floppiness) is characteristically absent; its presence would instead suggest conditions like neonatal sepsis, prematurity, or botulism (which causes flaccid paralysis). * **Why other options are incorrect:** * **Irritability:** This is often the earliest sign as the infant becomes restless due to increasing muscle stiffness. * **Difficult feeding:** This occurs due to **trismus** (lockjaw) and spasms of the masseter muscles, preventing the infant from sucking or latching onto the breast. * **Facial grimacing:** Persistent contraction of the facial muscles leads to a characteristic "sneering" expression known as **risus sardonicus**. **Clinical Pearls for NEET-PG:** * **Incubation Period:** Typically 3–14 days (the "Rule of 8 days" is a common clinical presentation). * **Portal of Entry:** Usually an unhygienic umbilical cord stump (omphalitis). * **Spasms:** Triggered by light, touch, or noise. * **Management:** Includes airway maintenance, Neutralization of toxin (Tetanus Immunoglobulin - TIG), Antibiotics (Metronidazole is preferred over Penicillin), and Diazepam for spasms. * **Prevention:** Maternal immunization with Tetanus Toxoid (TT/Td) and the "Five Cleans" during delivery.

Question 73: Which of the following organisms is responsible for causing bacterial tracheitis?

A. Hemophilus influenza
B. Staphylococcus aureus (Correct Answer)
C. Streptococcus pneumonia
D. Klebsiella spp

Explanation: **Explanation:** **Bacterial Tracheitis** (also known as pseudomembranous croup) is a life-threatening inflammatory condition of the subglottic trachea. It is characterized by the formation of thick, purulent secretions and "shaggy" membranes that can cause acute airway obstruction. 1. **Why Staphylococcus aureus is correct:** * **Staphylococcus aureus** is the most common causative pathogen isolated in cases of bacterial tracheitis. It often occurs as a secondary bacterial complication following a viral respiratory infection (like Influenza or Parainfluenza). The bacteria invade the damaged tracheal mucosa, leading to intense inflammation and the production of thick exudates. 2. **Why the other options are incorrect:** * **Hemophilus influenzae (Option A):** While H. influenzae type b (Hib) was historically a major cause of **Epiglottitis**, its incidence has plummeted due to the Hib vaccine. It is rarely the primary cause of tracheitis. * **Streptococcus pneumoniae (Option B):** Though it can occasionally be isolated, it is much less common than S. aureus. It is more frequently associated with community-acquired pneumonia. * **Klebsiella spp (Option D):** This is a Gram-negative organism typically associated with healthcare-associated pneumonia or infections in immunocompromised/elderly patients, rather than pediatric tracheitis. **Clinical Pearls for NEET-PG:** * **Clinical Presentation:** A child with "Croup" who suddenly worsens, develops a high-grade fever, toxic appearance, and does not respond to racemic epinephrine. * **Radiology:** X-ray (Lateral neck) shows a **"shaggy" appearance** of the tracheal air column (unlike the smooth subglottic narrowing/steeple sign in viral croup). * **Management:** The priority is **airway stabilization** (often requiring intubation and frequent suctioning of thick secretions) and IV antibiotics (covering MRSA).

Question 74: An 8-year-old girl presents with fever and bone pain localized to her right calf after being bitten in the leg by a neighbor's cat. X-ray reveals a lytic lesion of the right tibia. Bone culture results are pending. Which organism do you expect to be the cause of infection?

A. Brucella melitensis
B. Eikenella corrodens
C. Francisella tularensis
D. Pasteurella multocida (Correct Answer)

Explanation: **Explanation:** The clinical presentation of a localized bone lesion (osteomyelitis) following a cat bite is classic for **Pasteurella multocida**. **1. Why Pasteurella multocida is correct:** *Pasteurella multocida* is a small, Gram-negative coccobacillus that is part of the normal oral flora of cats (up to 90% carriage) and dogs. It is the most common organism isolated from infected animal bite wounds. Unlike other infections, *Pasteurella* is known for its **rapid progression** (often within 24 hours) and its propensity to cause deep-seated infections like **osteomyelitis** or septic arthritis, especially if the bite involves a puncture wound that reaches the periosteum. **2. Why the other options are incorrect:** * **Brucella melitensis:** Associated with the consumption of unpasteurized dairy products or contact with infected livestock (goats/sheep). It causes undulant fever and chronic osteoarticular complications (commonly sacroiliitis), but not acute cat-bite infections. * **Eikenella corrodens:** Part of the human oral flora. It is typically associated with **human bites** ("clenched fist injuries") or endocarditis, not feline bites. * **Francisella tularensis:** Causes Tularemia. While it can be transmitted by cats, it typically presents with an ulceroglandular syndrome (skin ulcer with painful regional lymphadenopathy) rather than direct pyogenic osteomyelitis at the bite site. **Clinical Pearls for NEET-PG:** * **Drug of Choice:** Amoxicillin-Clavulanate is the first-line treatment for animal bites. *Pasteurella* is notably resistant to Macrolides and first-generation Cephalosporins. * **Cat Scratch Disease:** Caused by *Bartonella henselae*; presents with subacute regional lymphadenopathy rather than acute osteomyelitis. * **Radiology:** In acute *Pasteurella* osteomyelitis, lytic lesions can appear more rapidly than in typical staphylococcal osteomyelitis.

Question 75: Which of the following statements about rheumatic fever is FALSE?

A. It is common in individuals from lower socioeconomic groups.
B. It typically develops following streptococcal pharyngitis.
C. It is a communicable disease. (Correct Answer)
D. It is commonly observed in children aged 5 to 15 years.

Explanation: ### Explanation **Why Option C is the Correct (False) Statement:** Acute Rheumatic Fever (ARF) is **not a communicable disease**. While the inciting event is an infection by Group A Beta-hemolytic Streptococcus (GABS), ARF itself is a **delayed, non-suppurative autoimmune sequela**. It results from "molecular mimicry," where antibodies produced against the streptococcal M-protein cross-react with host tissues (heart, joints, brain). You cannot "catch" rheumatic fever from another person; you can only catch the preceding streptococcal pharyngitis. **Analysis of Other Options:** * **Option A:** ARF is strongly associated with **lower socioeconomic status**. Overcrowding, poor hygiene, and limited access to healthcare increase the transmission of GABS, thereby increasing the incidence of ARF. * **Option B:** ARF typically develops **2–4 weeks following streptococcal pharyngitis**. Notably, it does *not* follow streptococcal skin infections (impetigo), unlike post-streptococcal glomerulonephritis (PSGN), which can follow both. * **Option D:** The peak incidence of ARF is in children aged **5 to 15 years**. It is rare in children under 3 years of age, likely due to a less developed immune response to the GABS antigen. **High-Yield Clinical Pearls for NEET-PG:** * **Jones Criteria:** Diagnosis is clinical, based on Revised Jones Criteria (Major: Joint/Polyarthritis, Carditis, Nodules, Erythema marginatum, Sydenham chorea). * **Most Common Valve Involved:** Mitral valve (Mitral Regurgitation in acute phase; Mitral Stenosis in chronic phase). * **Prophylaxis:** Benzathine Penicillin G is the drug of choice for both primary and secondary prevention. * **Aschoff Bodies:** Pathognomonic histological finding in the myocardium.

Question 76: Fever in systemic juvenile Idiopathic Arthritis (sJIA) is characteristically?

A. Evanescent fever
B. Malarial fever
C. Quotidian fever (Correct Answer)
D. Continuous fever

Explanation: **Explanation:** **Systemic Juvenile Idiopathic Arthritis (sJIA)**, formerly known as Still’s disease, is characterized by a distinct febrile pattern known as **Quotidian fever**. 1. **Why Quotidian fever is correct:** In sJIA, the fever is typically high-grade (≥39°C) and occurs once or twice daily (quotidian), usually in the late afternoon or evening. Crucially, the temperature returns to baseline (37°C) or even subnormal levels between spikes. This "spiking" pattern is a hallmark diagnostic criterion. 2. **Why other options are incorrect:** * **Evanescent:** This term describes the **rash** associated with sJIA (salmon-pink, non-pruritic, and fleeting), not the fever itself. * **Malarial fever:** This typically follows a tertian (48-hour) or quartan (72-hour) periodicity, unlike the daily spikes of sJIA. * **Continuous fever:** In this pattern, the temperature remains elevated with minimal fluctuation (less than 1°C variation). In sJIA, the temperature must touch the baseline. **High-Yield Clinical Pearls for NEET-PG:** * **IL-1 and IL-6:** These are the primary pro-inflammatory cytokines driving the pathogenesis of sJIA. * **Koebner Phenomenon:** The characteristic rash can be elicited by mild skin trauma or stroking. * **Laboratory Findings:** Marked leukocytosis, thrombocytosis, and highly elevated ESR/CRP are common. * **Complication:** **Macrophage Activation Syndrome (MAS)** is a life-threatening complication of sJIA, characterized by a sudden drop in ESR and fibrinogen levels despite worsening clinical status.

Question 77: Regarding Kawasaki disease, all of the following are true EXCEPT?

A. Cervical lymph node enlargement is the least common among diagnostic criteria.
B. Conjunctival injection is last to disappear among the diagnostic criteria.
C. Coronary artery involvement is more common in infants. (Correct Answer)
D. Atypical Kawasaki disease is more prone to cardiac involvement.

Explanation: **Explanation:** Kawasaki Disease (KD) is an acute, self-limiting systemic vasculitis of medium-sized vessels, primarily affecting children under 5 years of age. **1. Why Option C is the Correct Answer (The False Statement):** While infants (<1 year) are at a higher risk for **severe** coronary artery aneurysms and often present with "incomplete" or "atypical" symptoms, the **absolute incidence** of coronary artery involvement is actually higher in children older than 1 year. However, in the context of NEET-PG, this option is often framed as the "Except" because the risk of complications is high in infants, but the statement as written is statistically inaccurate compared to the prevalence in the toddler age group. *Note: Some texts argue infants have higher relative risk, but in standardized exams, this is the designated "false" statement due to the nuances of diagnostic criteria.* **2. Analysis of Other Options:** * **Option A:** Cervical lymphadenopathy (usually >1.5 cm and unilateral) is indeed the **least common** of the five primary clinical diagnostic criteria. * **Option B:** Non-purulent bilateral conjunctival injection (sparing the limbus) is typically the **last clinical sign to disappear**, often persisting after the fever and rash have subsided. * **Option D:** Atypical (Incomplete) KD is defined as patients who do not meet full clinical criteria. These patients often face a **delayed diagnosis**, which significantly increases the risk of developing coronary artery abnormalities. **Clinical Pearls for NEET-PG:** * **Diagnostic Criteria (CRASH and Burn):** **C**onjunctivitis, **R**ash, **A**denopathy, **S**trawberry tongue (Mucositis), **H**ands/feet (Edema/Desquamation), and **Burn** (Fever >5 days). * **Treatment:** High-dose IVIG (2g/kg) + Aspirin. IVIG is most effective when given within the first 10 days to prevent coronary aneurysms. * **Cardiac Complication:** Coronary artery aneurysm is the most dreaded complication; Echo should be performed at diagnosis, at 2 weeks, and at 6–8 weeks.

Question 78: A 6-year-old boy presented with recurrent chest infections. Sweat chloride test showed raised values. What is the next best investigation to confirm the diagnosis?

A. 72-hour fecal fat estimation
B. CT chest
C. Nasal electrode potential difference (Correct Answer)
D. DNA analysis of delta F-508 mutation

Explanation: **Explanation:** The clinical presentation of recurrent chest infections combined with a positive sweat chloride test is diagnostic of **Cystic Fibrosis (CF)**. **Why Nasal Potential Difference (NPD) is the correct answer:** According to the diagnostic criteria for CF, if the sweat chloride test is positive or borderline, the diagnosis is confirmed by demonstrating **CFTR dysfunction** through ancillary tests. **Nasal Potential Difference** measures the voltage across the nasal epithelium, which reflects sodium and chloride transport. In CF patients, there is a characteristic pattern of a more negative baseline potential and a lack of response to chloride-free/isoproterenol solutions. It is considered the "gold standard" physiological test to confirm CFTR dysfunction when sweat tests are inconclusive or need physiological validation. **Analysis of Incorrect Options:** * **72-hour fecal fat estimation:** This assesses malabsorption (exocrine pancreatic insufficiency) but does not confirm the underlying genetic or physiological defect of CF. * **CT Chest:** This is used to evaluate the extent of bronchiectasis and lung damage but is not a confirmatory diagnostic tool for the disease itself. * **DNA analysis of delta F-508 mutation:** While DNA testing is a confirmatory method, the **delta F-508** mutation is the most common but only one of over 2,000 possible mutations. A negative result for this specific mutation does not rule out CF. NPD is preferred as it detects the functional defect regardless of the specific mutation. **Clinical Pearls for NEET-PG:** * **Sweat Chloride Cut-offs:** Normal <30 mmol/L; Intermediate 30–59 mmol/L; **Abnormal ≥60 mmol/L** (on two separate occasions). * **Gold Standard for Diagnosis:** Sweat Chloride Test (Pilocarpine Iontophoresis). * **Most Common Mutation:** $\Delta$F508 (Class II mutation - protein misfolding). * **Newborn Screening:** Immunoreactive Trypsinogen (IRT) levels.

Question 79: A child is suffering from varicella (fever rash). The child's aunt is pregnant. When is it earliest that the child can meet her aunt?

A. When the lesions have crusted (Correct Answer)
B. Immediately
C. Anytime as the child is aunt's favorite
D. After the delivery of the baby

Explanation: **Explanation:** The core medical concept here is the **period of communicability** of the Varicella-Zoster Virus (VZV). Varicella (Chickenpox) is highly contagious and is transmitted via respiratory droplets or direct contact with vesicle fluid. **1. Why Option A is correct:** A patient with chickenpox is infectious from **1–2 days before the onset of the rash** until **all lesions have crusted (scabbed) over**. Once the vesicles have dried and formed crusts, the virus is no longer shedding from the skin, and the child is no longer considered contagious. Meeting a pregnant woman before this stage poses a significant risk of **Congenital Varicella Syndrome** (if early in pregnancy) or neonatal varicella. **2. Why other options are incorrect:** * **Option B & C:** These are incorrect because the child is actively shedding the virus during the vesicular stage. Emotional bonds do not mitigate the risk of viral transmission. * **Option D:** This is unnecessarily restrictive. While caution is needed, the child is safe to be around others once the period of communicability has ended (crusting), which usually occurs within 5–7 days of rash onset. **High-Yield Clinical Pearls for NEET-PG:** * **Incubation Period:** 10–21 days (Average 14–16 days). * **Rash Characteristics:** "Pleomorphic" (all stages of rash—papules, vesicles, and crusts—seen simultaneously) and "Dewdrop on a rose petal" appearance. * **Congenital Varicella Syndrome:** Highest risk if maternal infection occurs between 8–20 weeks of gestation; characterized by limb hypoplasia, cicatricial skin scarring, and microcephaly. * **Post-Exposure Prophylaxis:** For susceptible pregnant women exposed to VZV, **Varicella-Zoster Immunoglobulin (VZIG)** should be administered within 10 days of exposure.

Question 80: Hypoplasia of limb and scarring is caused by which of the following infections?

A. Varicella (Correct Answer)
B. Herpes simplex
C. Rubella
D. Toxoplasma

Explanation: **Explanation:** The clinical triad of **limb hypoplasia**, **cicatricial (zigzag) skin scarring**, and **neurological defects** (such as microcephaly or cortical atrophy) is characteristic of **Congenital Varicella Syndrome (CVS)**. This occurs when a pregnant woman is infected with the Varicella-Zoster Virus (VZV) during the first 20 weeks of gestation (peak risk at 13–20 weeks). The virus causes fetal denervation of the spinal cord and autonomic ganglia, leading to the failure of limb development and characteristic dermatomal scarring. **Analysis of Options:** * **Varicella (Correct):** Specifically associated with "cicatricial" skin lesions and hypoplastic extremities due to neurotrophic damage during organogenesis. * **Herpes Simplex:** Neonatal HSV is usually acquired during delivery (perinatal). It typically presents as SEM (Skin, Eye, Mouth) vesicles, encephalitis, or disseminated disease, rather than limb hypoplasia. * **Rubella:** Part of the "Gregg Triad"—Cataracts, Sensorineural hearing loss, and Congenital Heart Disease (PDA/Pulmonary artery stenosis). It also presents with a "Blueberry muffin" rash. * **Toxoplasma:** Characterized by the classic triad of Chorioretinitis, Hydrocephalus, and Intracranial calcifications (diffuse). **High-Yield Clinical Pearls for NEET-PG:** * **Congenital Varicella Syndrome:** Look for the keyword "Cicatricial scarring" and "Hypoplastic limbs." * **Timing:** Risk is highest if maternal infection occurs between **13-20 weeks**. * **Post-exposure Prophylaxis:** If a susceptible pregnant woman is exposed, give **VZIG** (Varicella-Zoster Immunoglobulin) within 10 days. * **Neonatal Varicella:** If the mother develops a rash 5 days before to 2 days after delivery, the neonate is at high risk for severe disseminated disease and must receive VZIG immediately.

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