Infectious Diseases Practice Questions

Q: Increased sweat chloride is seen in all conditions except?

Obesity. The sweat chloride test is the gold standard for diagnosing Cystic Fibrosis (CF), but several non-CF conditions can cause false-positive elevations. **Explanation of the Correct Answer:** **Obesity (Option D)** is the correct answer because it is **not** associated with increased sweat chloride levels. In fact, there is no physiological mechanism linking excess adipose tissue to impaired chloride transport in the eccrine glands. **Explanation of Incorrect Options:** * **Ectodermal Dysplasia (Option A):** This genetic disorder affects the development of sweat glands. Structural abnormalities in these glands can lead to an inability to reabsorb chloride, resulting in elevated levels. * **Nephrogenic Diabetes Insipidus (Option B):** Chronic dehydration and electrolyte imbalances associated with NDI can lead to concentrated sweat and elevated chloride readings. * **Glucose-6-Phosphatase Deficiency (Option C):** Also known as Von Gierke Disease (GSD Type I). The exact mechanism is complex but involves metabolic derangements that interfere with normal ion transport in sweat ducts. **High-Yield Clinical Pearls for NEET-PG:** * **Thresholds:** Sweat chloride **>60 mmol/L** is diagnostic for CF; **40–59 mmol/L** is intermediate/borderline. * **Other False Positives:** Adrenal insufficiency (Addison’s), Hypothyroidism, Malnutrition (Anorexia), Mucopolysaccharidosis, and Fucosidosis. * **False Negatives:** Edema (hypoproteinemia) and technical errors (inadequate sweat collection). * **The "Gold Standard" Method:** Quantitative pilocarpine iontophoresis.

Q: Which of the following is NOT true about Herpangina?

More severe than primary herpetic gingivostomatitis. **Explanation:** Herpangina is a common viral infection in children, primarily caused by **Coxsackievirus A**. Understanding its clinical presentation is crucial for differentiating it from other pediatric oral lesions. **1. Why Option C is the correct answer (The False Statement):** Contrary to the option, **Herpangina is generally milder** than Primary Herpetic Gingivostomatitis (PHGS). PHGS, caused by HSV-1, typically presents with high-grade fever, significant malaise, extensive friable/bleeding gums, and widespread oral ulcerations. Herpangina, while uncomfortable, usually involves fewer lesions and a faster recovery period (3–5 days). **2. Analysis of Incorrect Options (True Statements):** * **Option A (Epidemics):** Herpangina frequently occurs in seasonal outbreaks, particularly during summer and autumn months, often spreading in daycare settings. * **Option B (Site Specific):** This is a hallmark diagnostic feature. Lesions in Herpangina are localized to the **posterior oropharynx**, specifically the soft palate, uvula, and tonsillar pillars. In contrast, HSV lesions are usually anterior. * **Option D (Gingivitis is absent):** This is the key clinical differentiator. In Herpangina, the gingiva (gums) are spared. In Primary Herpetic Gingivostomatitis, **gingivitis** (swollen, red, bleeding gums) is a pathognomonic finding. **Clinical Pearls for NEET-PG:** * **Etiology:** Coxsackievirus A (most common); also Coxsackie B and Echoviruses. * **Hand-Foot-Mouth Disease (HFMD):** Caused by Coxsackie A16 or Enterovirus 71; presents like Herpangina but includes a maculopapular/vesicular rash on palms and soles. * **Treatment:** Purely supportive (hydration and analgesics); antibiotics and acyclovir have no role in Herpangina.

Q: A pregnant female is infected with Rubella. Which of the following immunoglobulins is produced by in-utero infection?

IgM. **Explanation:** The correct answer is **IgM**. **Why IgM is correct:** The human fetus begins producing its own immunoglobulins around the 20th week of gestation. However, the placenta is selective; only maternal **IgG** can cross the placental barrier to provide passive immunity. **IgM** is a pentameric molecule with a high molecular weight, making it too large to cross the placenta. Therefore, if IgM antibodies against Rubella are detected in a newborn or a fetus, it serves as definitive evidence of a **primary intrauterine infection**, as these antibodies could only have been synthesized by the fetal immune system in response to the virus. **Why other options are incorrect:** * **IgG:** While IgG is found in the fetus, it is predominantly of maternal origin (passive transfer). It does not signify an active fetal infection unless titers remain persistently high or rise after the disappearance of maternal antibodies (usually after 6–12 months). * **IgA:** IgA is primarily secreted in colostrum and breast milk. While the fetus can produce trace amounts, it is not the diagnostic marker for acute in-utero infection. * **IgD:** This immunoglobulin acts mainly as an antigen receptor on B cells and has no diagnostic significance in congenital infections. **High-Yield Clinical Pearls for NEET-PG:** * **Gregg’s Triad (Congenital Rubella Syndrome):** Cataracts, Sensorineural hearing loss (most common), and Congenital Heart Disease (PDA is most common; Peripheral Pulmonary Artery Stenosis is most specific). * **Blueberry Muffin Rash:** Characteristic finding in CRS due to extramedullary hematopoiesis. * **Risk Period:** The risk of malformation is highest if the infection occurs in the **first trimester** (up to 80% risk in the first 12 weeks). * **Diagnosis:** Detection of Rubella-specific IgM in the cord blood or neonatal serum is the gold standard for diagnosing CRS at birth.

Q: Pastia's lines are seen in which condition?

Scarlet fever. **Explanation:** **Scarlet Fever (Option D)** is the correct answer. It is caused by Group A Beta-hemolytic *Streptococcus* (GABHS) which produces **erythrogenic toxins**. **Pastia’s lines** (or Thompson’s lines) are a classic clinical sign characterized by linear petechiae or pink/red lines found in the skin folds, particularly the antecubital fossa, axilla, and groin. These lines occur because the rash is more intense in areas of skin friction and capillary fragility. **Analysis of Incorrect Options:** * **Measles (Option A):** Characterized by **Koplik spots** (enanthem) and a maculopapular rash that starts behind the ears and spreads downwards. It does not feature Pastia’s lines. * **Varicella (Option B):** Presents with a pleomorphic rash (macules, papules, vesicles, and crusts appearing simultaneously) often described as **"dewdrops on a rose petal."** * **Syphilis (Option C):** Secondary syphilis presents with a generalized maculopapular rash involving the **palms and soles**, but not linear petechiae in skin folds. **High-Yield Clinical Pearls for Scarlet Fever:** 1. **Sandpaper Rash:** The rash has a rough, "sunburn-with-goosebumps" texture. 2. **Strawberry Tongue:** Initially "White Strawberry Tongue" (coated), followed by "Red Strawberry Tongue" (denuded papillae). 3. **Circumoral Pallor:** Redness of the face with a distinct pale area around the mouth. 4. **Schultz-Charlton Reaction:** Blanching of the scarlet fever rash when specific antitoxin is injected (historical diagnostic test). 5. **Dick Test:** Used to determine susceptibility to scarlet fever.

Q: The classic triad of congenital rubella includes all of the following except?

Retinitis. The classic triad of Congenital Rubella Syndrome (CRS), also known as **Gregg’s Triad**, consists of specific ocular, auditory, and cardiac malformations. **Explanation of the Correct Answer:** **C. Retinitis** is the correct answer because it is not part of the classic triad. While ocular involvement is common in CRS, the hallmark finding is **Cataract** (typically bilateral and "pearly"). While "Salt and Pepper Retinopathy" is a frequent finding in CRS, it is not part of the defining triad and usually does not affect vision as severely as cataracts. **Explanation of Incorrect Options:** * **A. Cataract:** This is the primary ocular component of the triad. It results from the virus interfering with lens fiber development during the first trimester. * **B. Deafness:** Sensorineural hearing loss is the **most common** manifestation of CRS. It may be the only finding in late-gestation infections. * **D. Congenital Heart Disease:** This is the third component of the triad. The most characteristic lesion is **Patent Ductus Arteriosus (PDA)**, followed by peripheral pulmonary artery stenosis. **High-Yield Clinical Pearls for NEET-PG:** * **Most common finding:** Sensorineural hearing loss. * **Most common cardiac lesion:** PDA. * **Ocular findings:** "Pearly" cataracts, microphthalmia, and **Salt and Pepper Retinopathy** (the most common ocular sign, though not in the triad). * **Dermal finding:** "Blueberry muffin" spots (extramedullary hematopoiesis). * **Radiology:** "Celery stalking" (longitudinal radiolucent striations in the metaphysis of long bones). * **Risk:** The risk of fetal infection is highest (up to 90%) if the mother is infected before 11 weeks of gestation.

Q: The risk of neonatal chickenpox is maximum if maternal infection occurs:

Within five days of delivery. **Explanation:** The risk of severe neonatal chickenpox is highest when maternal varicella occurs **within 5 days before to 2 days after delivery**. This specific window is critical because of the timing of transplacental antibody transfer. When a mother develops varicella, it takes approximately 5 days for her body to produce **IgG antibodies**. If delivery occurs within this 5-day window, the virus crosses the placenta and infects the fetus, but the protective maternal antibodies have not yet developed or been transferred. Consequently, the neonate receives a high viral load without passive immunity, leading to severe, disseminated, and potentially fatal disease (neonatal varicella). **Analysis of Options:** * **Options A & B (First/Second Trimester):** Infection during early pregnancy (especially weeks 13–20) can lead to **Congenital Varicella Syndrome**, characterized by limb hypoplasia, cicatricial skin scarring, and microcephaly. While serious, the risk of transmission is low (~2%), and it does not cause the acute neonatal chickenpox described. * **Option D (Six weeks of delivery):** If infection occurs weeks before delivery, the mother has sufficient time to transfer protective IgG antibodies to the fetus, resulting in a much milder or asymptomatic course for the newborn. **High-Yield Clinical Pearls for NEET-PG:** * **Management:** If maternal infection occurs in the "danger window" (5 days before to 2 days after), the neonate must receive **Varicella-Zoster Immunoglobulin (VZIG)** immediately after birth. * **Treatment:** If the neonate develops symptoms, **Intravenous Acyclovir** is the treatment of choice. * **Incubation Period:** The incubation period for varicella is 10–21 days. * **Contagiousness:** Patients are contagious from 48 hours before the rash appears until all lesions have crusted over.

Q: A child presents with fever and redness of a cheek. What is the causative organism for this condition?

Parvovirus B-19. ### Explanation The clinical presentation of fever followed by a characteristic redness of the cheek (often described as a **"slapped-cheek" appearance**) is the hallmark of **Erythema Infectiosum**, also known as **Fifth Disease**. **1. Why Parvovirus B-19 is correct:** Parvovirus B-19 is a DNA virus that infects erythroid progenitor cells. In children, it typically presents with a mild prodromal fever followed by a bright red exanthem on the cheeks (sparing the nasolabial folds). As the facial rash fades, a secondary **"lace-like" or reticular rash** often appears on the trunk and extremities. The rash is immune-mediated and usually appears once the child is no longer contagious. **2. Why the other options are incorrect:** * **Herpes virus:** HSV-1 typically causes gingivostomatitis or herpetic whitlow. While it causes skin lesions, they are vesicular (fluid-filled) rather than a diffuse erythematous "slapped-cheek" rash. * **Adenovirus:** Commonly causes pharyngoconjunctival fever (fever, sore throat, and conjunctivitis). While it can cause a nonspecific rash, it does not present with the classic malar erythema of Fifth disease. * **Rubella:** Also known as German Measles, it presents with a maculopapular rash that starts on the face and spreads downward (cephalocaudal progression) along with characteristic **Forchheimer spots** on the soft palate and retroauricular lymphadenopathy. **Clinical Pearls for NEET-PG:** * **Aplastic Crisis:** Parvovirus B-19 can cause a life-threatening cessation of red blood cell production in patients with high RBC turnover (e.g., **Sickle Cell Anemia**, Hereditary Spherocytosis). * **Pregnancy:** Infection in pregnancy can lead to **Hydrops Fetalis** due to severe fetal anemia. * **Adults:** Often presents with arthralgia or symmetric arthritis rather than a rash. * **Receptor:** The virus enters cells via the **P-antigen** (globoside) on erythrocytes.

Q: Which of the following is NOT a complication of chickenpox?

Enteritis. **Explanation:** Chickenpox, caused by the **Varicella-Zoster Virus (VZV)**, is a highly contagious viral infection. While it is typically self-limiting in healthy children, it can lead to various systemic complications. **Why Enteritis is the Correct Answer:** Enteritis (inflammation of the small intestine) is **not** a recognized complication of chickenpox. VZV primarily targets the skin, respiratory system, and central nervous system. Gastrointestinal involvement is extremely rare and not part of the classic clinical spectrum of the disease. **Analysis of Incorrect Options:** * **Pneumonia:** This is the **most serious complication in adults** and immunocompromised individuals. It typically presents with cough and dyspnea 3–5 days after the rash appears. * **Meningitis/Encephalitis:** Neurological complications are well-documented. **Acute Cerebellar Ataxia** (presenting with nystagmus and unsteady gait) is the most common CNS complication in children, while encephalitis and aseptic meningitis can also occur. * **Reye’s Syndrome:** This is a rare but fatal condition involving acute encephalopathy and fatty liver degeneration. It is strongly associated with the use of **aspirin (salicylates)** during a viral prodrome like chickenpox or influenza. **High-Yield Clinical Pearls for NEET-PG:** * **Most common complication in children:** Secondary bacterial infection of skin lesions (usually *Staph. aureus* or *Group A Strep*). * **Congenital Varicella Syndrome:** Occurs if the mother is infected in the first 20 weeks of pregnancy; characterized by cicatricial skin scarring, limb hypoplasia, and microcephaly. * **Treatment of choice:** Oral Acyclovir (if started within 24 hours of rash) for high-risk cases; supportive care for healthy children. * **Prevention:** Live attenuated vaccine (Oka strain).

Question 1

A 9-year-old girl child developed a 10 mm area of induration on the left forearm 72 hours after intradermal injection of 0.1 ml of purified protein derivative (PPD). Which of the following is most likely to be seen on the X-ray of this patient?

Accepted Answer

No abnormal findings

Answer

Marked hilar adenopathy

Answer

Upper lobe calcifications

Answer

Reticulo-nodular densities

Question 2

Increased sweat chloride is seen in all conditions except?

Accepted Answer

Obesity

Answer

Ectodermal dysplasia

Answer

Nephrogenic diabetes insipidus

Answer

Glucose 6 phosphatase deficiency

Question 3

A 5-year-old unimmunized child presented with high fever, sore throat, dysphagia, and voice change. A throat swab from a whitish lesion was taken for diagnosis. What is the most likely diagnosis?

Accepted Answer

Diphtheria

Answer

Mumps

Answer

Pertussis

Answer

Streptococcal pharyngitis

Question 4

Which of the following is NOT true about Herpangina?

Accepted Answer

More severe than primary herpetic gingivostomatitis

Answer

Occurs in epidemics

Answer

Site specific (Occurs on palate and uvula)

Answer

Gingivitis is absent

Question 5

A pregnant female is infected with Rubella. Which of the following immunoglobulins is produced by in-utero infection?

Accepted Answer

IgM

Answer

IgG

Answer

IgA

Answer

IgD

Question 6

Pastia's lines are seen in which condition?

Accepted Answer

Scarlet fever

Answer

Measles

Answer

Varicella

Answer

Syphilis

Question 7

The classic triad of congenital rubella includes all of the following except?

Accepted Answer

Retinitis

Answer

Cataract

Answer

Deafness

Answer

Congenital Heart Disease

Question 8

The risk of neonatal chickenpox is maximum if maternal infection occurs:

Accepted Answer

Within five days of delivery

Answer

During the first trimester

Answer

During the second trimester

Answer

Within six weeks of delivery

Question 9

A child presents with fever and redness of a cheek. What is the causative organism for this condition?

Accepted Answer

Parvovirus B-19

Answer

Herpes virus

Answer

Adenovirus

Answer

Rubella

Question 10

Which of the following is NOT a complication of chickenpox?

Accepted Answer

Enteritis

Answer

Meningitis

Answer

Pneumonia

Answer

Reye's Syndrome

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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