Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 251: A 12-year-old boy presents with fever, sore throat, and cervical lymph node enlargement. A throat swab is positive for group A beta-hemolytic streptococci, and he is started on penicillin. However, his symptoms worsen despite treatment. What is the next best step?

A. Start azithromycin
B. Perform a blood monospot test and CBC (Correct Answer)
C. Check IgE for infectious mononucleosis
D. Presume Epstein-Barr virus infection and start acyclovir and prednisolone

Explanation: **Explanation:** The clinical presentation of fever, sore throat, and cervical lymphadenopathy is classic for both **Streptococcal Pharyngitis** and **Infectious Mononucleosis (IM)** caused by the Epstein-Barr Virus (EBV). The key diagnostic challenge here is that approximately **30% of patients with IM are co-colonized with Group A Streptococcus (GAS)**. The failure to improve on penicillin, combined with worsening symptoms, strongly suggests that the primary underlying pathology is IM rather than a simple bacterial infection. Therefore, the next best step is to confirm the diagnosis of IM using a **Monospot test** (to detect heterophile antibodies) and a **CBC** (to look for absolute lymphocytosis and atypical lymphocytes/Downey cells). **Analysis of Options:** * **Option A:** Switching to another antibiotic like Azithromycin is incorrect because the lack of response to Penicillin (the gold standard for GAS) suggests a non-bacterial etiology. * **Option C:** IgE levels are markers for allergic reactions, not IM. EBV-specific serology involves IgM/IgG against Viral Capsid Antigen (VCA), not IgE. * **Option D:** While IM is suspected, Acyclovir is not routinely recommended as it does not provide clinical benefit. Prednisolone is reserved only for complications like airway obstruction or severe thrombocytopenia. **High-Yield Pearls for NEET-PG:** 1. **The "Ampicillin Rash":** If a patient with IM is mistakenly treated with Ampicillin or Amoxicillin, 70–90% develop a characteristic maculopapular rash. 2. **Atypical Lymphocytes:** These are T-cells (CD8+) reacting against EBV-infected B-cells. 3. **Splenomegaly:** Patients must be advised to avoid contact sports for 3–4 weeks to prevent splenic rupture. 4. **Diagnosis:** Monospot test is the screening test of choice in adolescents; EBV-specific antibodies are preferred in children <4 years (who often have negative Monospot results).

Question 252: All of the following are true regarding congenital syphilis EXCEPT?

A. Rhinitis is an early sign
B. Notched incisors
C. Conductive hearing loss (Correct Answer)
D. Linear scars at the angle of mouth

Explanation: **Explanation:** Congenital syphilis is caused by the transplacental transmission of *Treponema pallidum*. The manifestations are traditionally divided into **Early** (appearing before 2 years of age) and **Late** (appearing after 2 years). **Why Option C is the correct answer (The Exception):** Congenital syphilis is associated with **Sensorineural hearing loss**, not conductive hearing loss. This occurs due to eighth cranial nerve (vestibulocochlear) involvement or labyrinthitis. It typically presents in late childhood or adolescence and is a key component of the classic **Hutchinson’s Triad** (Interstitial keratitis, Sensorineural deafness, and Hutchinson’s teeth). **Analysis of Incorrect Options:** * **Option A (Rhinitis):** Also known as "snuffles," this is often the **earliest** clinical sign of congenital syphilis. It is characterized by a highly infectious mucopurulent or bloody nasal discharge. * **Option B (Notched incisors):** Known as **Hutchinson’s teeth**, these are permanent upper central incisors that are peg-shaped, widely spaced, and notched. This is a classic late manifestation. * **Option D (Linear scars):** Known as **Rhagades**, these are linear scars at the angles of the mouth, nose, or anus resulting from the healing of painful fissures (syphilitic rhagades) seen in the neonatal period. **High-Yield Clinical Pearls for NEET-PG:** * **Hutchinson’s Triad:** Interstitial keratitis, 8th nerve deafness, Hutchinson’s teeth. * **Bone Signs:** Wimberger’s sign (localized destruction of the medial proximal tibial metaphysis) and Parrot’s pseudoparalysis (due to painful osteochondritis). * **Mulberry Molars:** Pitting of the occlusal surfaces of the first molars. * **Saddle Nose:** Deformity caused by the destruction of the nasal septum. * **Treatment:** Penicillin G is the drug of choice for all stages.

Question 253: A child presents with fever for 2 days, altered sensorium, and purpuric rashes. His blood pressure is 90/60 mmHg. What is the treatment of choice?

A. IV Quinine
B. IV Artesunate
C. IV Penicillin (Correct Answer)
D. Chloroquine

Explanation: ### Explanation **Correct Answer: C. IV Penicillin** The clinical triad of **fever, altered sensorium, and purpuric rashes** (petechiae or ecchymoses) is the classic presentation of **Meningococcemia** (caused by *Neisseria meningitidis*). The presence of purpura indicates a medical emergency, often progressing to Waterhouse-Friderichsen syndrome (adrenal hemorrhage and shock). **Why IV Penicillin?** Historically and for exam purposes, **IV Penicillin G** remains the treatment of choice for confirmed meningococcal disease due to its high efficacy and narrow spectrum. In empirical settings, third-generation cephalosporins (Ceftriaxone) are often used, but Penicillin is the definitive classic answer for *N. meningitidis*. It works by inhibiting bacterial cell wall synthesis. **Why the other options are incorrect:** * **A & B (IV Quinine / IV Artesunate):** These are treatments for severe/complicated **Malaria**. While cerebral malaria causes fever and altered sensorium, it does not typically present with a rapidly progressing purpuric rash. * **D (Chloroquine):** This is used for uncomplicated *P. vivax* malaria. It has no role in treating bacterial sepsis or meningococcemia. **Clinical Pearls for NEET-PG:** * **Drug of Choice for Chemoprophylaxis (Close Contacts):** Rifampicin (Adults/Children). Ciprofloxacin or Ceftriaxone are alternatives. * **Most Common Serogroup in India:** Historically Serogroup A; globally, Serogroups B and C are common. * **Characteristic Rash:** "Non-blanching" purpuric spots, often starting on the trunk and lower extremities. * **Initial Empirical Choice:** If the question asks for the *initial* empirical management before the organism is known, Ceftriaxone is preferred. However, for the specific entity of Meningococcemia, Penicillin is the gold standard.

Question 254: Which of the following statements regarding measles is false?

A. Koplik's spots cannot be seen in conjunctival or vaginal mucosa. (Correct Answer)
B. Vitamin A administration is part of the management of clinical measles.
C. CD 150 and PVRL4 are receptors for measles virus.
D. Pneumonia is the common cause of death in children with measles.

Explanation: ### Explanation **1. Why Option A is the correct (False) statement:** Koplik’s spots are the pathognomonic enanthem of measles. While they are most commonly found on the buccal mucosa opposite the lower second molars, they are **not** restricted to the mouth. These spots can also be seen on other mucosal surfaces, including the **conjunctiva, vaginal mucosa, and gastrointestinal tract**. Therefore, the statement that they "cannot be seen" in these areas is false. **2. Analysis of Incorrect Options (True statements):** * **Option B:** Vitamin A deficiency is a known risk factor for severe measles. The WHO recommends Vitamin A administration for all children with acute measles to reduce the risk of blindness, pneumonia, and mortality. * **Option C:** The measles virus enters host cells via specific receptors: **CD150** (also known as SLAM), found on immune cells, and **Nectin-4** (PVRL4), located on the basolateral surface of epithelial cells. * **Option D:** While diarrhea is the most common complication overall, **Pneumonia** (either primary viral or secondary bacterial) is the most common cause of measles-related death in children. **3. High-Yield Clinical Pearls for NEET-PG:** * **Incubation Period:** 10–14 days. * **Infectivity:** 4 days before to 4 days after the appearance of the rash. * **Subacute Sclerosing Panencephalitis (SSPE):** A late, fatal neurological complication occurring years after the initial infection. * **Modified Measles:** Occurs in individuals with partial immunity (e.g., those who received IG); it has a longer incubation period and milder symptoms. * **Warthin-Finkeldey Cells:** Multinucleated giant cells pathognomonic for measles found in lymphoid tissue.

Question 255: What is the commonest age group for infant botulism?

A. 1 to 3 weeks
B. 2 to 4 months (Correct Answer)
C. 10 to 12 months
D. 7 to 9 months

Explanation: **Explanation:** Infant botulism is caused by the ingestion of *Clostridium botulinum* spores (commonly from honey or environmental soil/dust), which germinate and produce toxins in the immature intestinal tract of infants. **Why 2 to 4 months is correct:** While infant botulism can occur between 1 week and 12 months of age, the **peak incidence is between 2 and 4 months**. This specific window corresponds to the period when the infant’s intestinal microflora is still developing and the gastric acidity is relatively low, providing an ideal environment for spore germination and toxin production. By the time an infant reaches the latter half of their first year, a more mature gut microbiome provides "colonization resistance," making it harder for *C. botulinum* to establish itself. **Analysis of Incorrect Options:** * **A (1 to 3 weeks):** Though possible, it is rare. Most cases require a period of environmental exposure and a specific stage of gut maturation that typically peaks later than the neonatal period. * **C & D (7 to 12 months):** As infants grow older and start solid foods, their intestinal flora becomes more diverse and protective. The risk significantly declines after 6 months of age. **High-Yield Clinical Pearls for NEET-PG:** * **Classic Presentation:** "Floppy Baby" syndrome—characterized by constipation (often the first sign), weak cry, poor sucking reflex, and symmetric descending paralysis. * **Source:** Honey is the most identified dietary reservoir; hence, it is contraindicated for children under 1 year. * **Diagnosis:** Identification of *C. botulinum* spores or toxin in the **stool** (toxin is rarely found in the blood in infant botulism, unlike foodborne botulism). * **Treatment:** Intravenous **Botulism Immune Globulin (BabyBIG)**. Avoid antibiotics (like aminoglycosides) as they may worsen paralysis by releasing more toxin.

Question 256: A child is born with meningoencephalitis, chorioretinitis, and intracranial calcification. What is the most likely diagnosis?

A. Congenital syphilis
B. Toxoplasmosis (Correct Answer)
C. Rubella
D. Herpes simplex

Explanation: ### Explanation The clinical presentation described is the classic **Sabin Triad**, which is pathognomonic for **Congenital Toxoplasmosis**. This condition is caused by the protozoan *Toxoplasma gondii*, typically transmitted to the fetus when a non-immune mother acquires a primary infection during pregnancy. **1. Why Toxoplasmosis is Correct:** The triad consists of: * **Chorioretinitis:** The most common finding, often leading to vision loss. * **Hydrocephalus/Meningoencephalitis:** Resulting from inflammatory obstruction of CSF pathways. * **Intracranial Calcifications:** Characteristically **diffuse and scattered** throughout the brain parenchyma (unlike CMV, which are periventricular). **2. Why Other Options are Incorrect:** * **Congenital Syphilis:** Presents with snuffles (rhinitis), Hutchinson’s teeth, Mulberry molars, and periostitis. It does not typically cause intracranial calcifications. * **Rubella:** Characterized by the **Gregg Triad**: Sensorineural hearing loss, Congenital Cataracts, and Heart defects (Patent Ductus Arteriosus). * **Herpes Simplex (HSV-2):** Usually presents as a neonatal infection (acquired during birth) with skin-eye-mouth (SEM) vesicles, seizures, or disseminated multiorgan failure, rather than a congenital malformation triad. **3. High-Yield Clinical Pearls for NEET-PG:** * **Calcification Pattern:** Toxoplasmosis = Diffuse/Scattered; CMV = Periventricular. * **Treatment:** The standard regimen is **Pyrimethamine, Sulfadiazine, and Folinic acid** for one year. * **Diagnosis:** Initial screening via maternal serology; confirmed in the neonate via PCR of amniotic fluid or IgM/IgA antibodies. * **Classic Sign:** "Macular star" or "punched-out" chorioretinal lesions on fundoscopy.

Question 257: According to NACO guidelines, which of the following is NOT an indication for starting Antiretroviral Therapy (ART) in children?

A. Infants < 11 months with CD4 count < 1500 cells/mm³
B. Children 12-35 months with CD4 count < 500 cells/mm³
C. Children 36-59 months with CD4 count < 350 cells/mm³
D. All of the above are indications for ART (Correct Answer)

Explanation: **Explanation:** The National AIDS Control Organization (NACO) guidelines have evolved toward a **"Treat All"** policy. However, for examination purposes, it is crucial to understand the specific immunological thresholds that define the urgency of starting Antiretroviral Therapy (ART) in children. **1. Why the Correct Answer is Right:** According to the latest NACO guidelines, **all HIV-infected children should be started on ART regardless of their clinical stage or CD4 count.** Therefore, the scenarios described in options A, B, and C are all valid indications for initiating treatment. The underlying medical concept is that early initiation of ART significantly reduces morbidity and mortality, prevents opportunistic infections, and preserves immune function in the pediatric population. **2. Analysis of Options:** * **Option A:** In infants (<12 months), the risk of rapid disease progression is extremely high. A CD4 count <1500 cells/mm³ (or <25%) is a critical threshold, but under current guidelines, even those with higher counts must start ART immediately upon diagnosis. * **Option B & C:** For children aged 12–59 months, while the "Treat All" policy applies, historical thresholds (CD4 <750 or <25% for 12–35 months; CD4 <350 for older children) are still tested to ensure students recognize that these levels represent significant immunosuppression requiring mandatory intervention. **3. High-Yield Clinical Pearls for NEET-PG:** * **Treat All Policy:** Since 2017, NACO recommends ART for all HIV-positive individuals (infants, children, adolescents, and adults) irrespective of CD4 count or WHO clinical stage. * **Preferred First-line Regimen (Pediatric):** The current preferred regimen for children is **Abacavir (ABC) + Lamivudine (3TC) + Dolutegravir (DTG)**, provided the child weighs at least 3 kg. * **Diagnosis:** In infants <18 months, HIV is diagnosed using **Virological testing (DNA-PCR)** because maternal antibodies (IgG) can persist, making ELISA unreliable.

Question 258: What is the recommended daily dose of Isoniazid for a child in the DOTS regimen under RNTCP?

A. 10-15 mg/kg/day (Correct Answer)
B. 15-20 mg/kg/day
C. 20-25 mg/kg/day
D. 5-10 mg/kg/day

Explanation: The correct answer is **A. 10-15 mg/kg/day**. ### **Explanation** Under the Revised National Tuberculosis Control Programme (RNTCP), now known as the National TB Elimination Programme (NTEP), the dosage of anti-tubercular drugs (ATD) for pediatric patients is higher than for adults due to faster metabolism in children. For **Isoniazid (H)**, the recommended daily dose is **10 mg/kg (range 10–15 mg/kg)**. This dosage ensures therapeutic serum concentrations necessary to achieve bactericidal action against rapidly dividing mycobacteria. ### **Analysis of Incorrect Options** * **Option B (15-20 mg/kg/day):** This range is higher than the standard recommendation for Isoniazid. However, it is the recommended dose for **Ethambutol (E)** in children (range 15–25 mg/kg). * **Option C (20-25 mg/kg/day):** This is the dosage range for **Pyrazinamide (Z)** (range 30–35 mg/kg) or the upper limit for Ethambutol. Using this dose for Isoniazid significantly increases the risk of hepatotoxicity. * **Option D (5-10 mg/kg/day):** This is the standard dose for **adults** (5 mg/kg). In children, this dose would be sub-therapeutic, leading to treatment failure and potential drug resistance. ### **High-Yield Clinical Pearls for NEET-PG** * **Daily Regimen:** NTEP has shifted from intermittent (thrice weekly) to **daily fixed-dose combinations (FDC)** based on weight bands. * **Rifampicin (R) Dose:** 10–15 mg/kg/day. * **Pyrazinamide (Z) Dose:** 30–35 mg/kg/day. * **Ethambutol (E) Dose:** 15–25 mg/kg/day. * **Pyridoxine Supplementation:** Always co-administer Pyridoxine (10 mg/day) with Isoniazid in children to prevent peripheral neuropathy, especially in malnourished children or infants on exclusive breastfeeding. * **Hepatotoxicity:** Isoniazid is the most common cause of drug-induced liver injury in the intensive phase.

Question 259: A four-year-old child presents with mild fever, malaise, purpura, arthritis, abdominal pain, and microscopic hematuria. What is the most likely diagnosis?

A. Thrombasthenia
B. Idiopathic thrombocytopenic purpura
C. Systemic Lupus Erythematosus
D. Henoch-Schonlein purpura (Correct Answer)

Explanation: ### Explanation **Henoch-Schönlein Purpura (HSP)**, now commonly referred to as **IgA Vasculitis**, is the most common systemic vasculitis in children. It is a small-vessel vasculitis characterized by the deposition of IgA-dominant immune complexes. #### Why Option D is Correct: The diagnosis of HSP is clinical and typically presents with a classic tetrad of symptoms, all of which are present in this case: 1. **Palpable Purpura:** Usually distributed over the buttocks and lower extremities (gravity-dependent areas) without thrombocytopenia. 2. **Arthritis/Arthralgia:** Migratory polyarthritis, commonly affecting knees and ankles. 3. **Abdominal Pain:** Caused by bowel wall edema and hemorrhage; can lead to intussusception. 4. **Renal Involvement:** Manifests as microscopic hematuria or proteinuria (HSP Nephritis). #### Why Other Options are Incorrect: * **A. Thrombasthenia (Glanzmann’s):** A qualitative platelet disorder (GP IIb/IIIa deficiency) presenting with mucosal bleeding and prolonged bleeding time, not with arthritis or abdominal pain. * **B. Idiopathic Thrombocytopenic Purpura (ITP):** Presents with isolated thrombocytopenia and petechiae/ecchymosis. It lacks the systemic features of arthritis, abdominal pain, and hematuria. * **C. Systemic Lupus Erythematosus (SLE):** While it can cause arthritis and nephritis, it is rare in a 4-year-old (more common in adolescent females) and typically presents with a malar rash and positive ANA/anti-dsDNA. #### High-Yield Clinical Pearls for NEET-PG: * **Preceding Event:** Often follows an Upper Respiratory Tract Infection (URTI). * **Platelet Count:** Characteristically **normal** (distinguishes it from ITP). * **Most Common Complication:** Intussusception (typically **ileo-ileal**, unlike the common ileo-colic type). * **Prognosis:** Generally excellent; long-term prognosis depends entirely on the severity of **renal involvement**. * **Biopsy:** Shows leukocytoclastic vasculitis with IgA deposition.

Question 260: What is the treatment for a child with frequent tapeworm infestation?

A. Albendazole
B. Niclosamide
C. Praziquantel
D. All of the above (Correct Answer)

Explanation: **Explanation:** The treatment of tapeworm infestation (Cestodiasis) in children involves several anthelmintic agents, each targeting the parasite through different mechanisms. The correct answer is **"All of the above"** because Albendazole, Niclosamide, and Praziquantel are all clinically recognized treatments for various tapeworm species (such as *Taenia saginata*, *Taenia solium*, and *Hymenolepis nana*). * **Praziquantel (Option C):** This is the **drug of choice** for most adult tapeworm infections. It works by increasing the permeability of the parasite's cell membrane to calcium, causing strong contractions and paralysis (spastic paralysis), leading to the detachment of the scolex from the intestinal wall. * **Niclosamide (Option B):** This is a second-line alternative. It acts locally in the intestine by inhibiting oxidative phosphorylation in the mitochondria of the tapeworm. It kills the worm on contact but does not affect the larval stages (cysticerci). * **Albendazole (Option A):** While primarily used for nematodes (roundworms), high-dose or prolonged courses of Albendazole are effective against cestodes. It is specifically the **drug of choice for cysticercosis** (the larval stage of *T. solium*) and Hydatid disease (*Echinococcus*). **High-Yield NEET-PG Pearls:** 1. **Drug of Choice for Neurocysticercosis (NCC):** Albendazole is preferred over Praziquantel because it has better CNS penetration and higher efficacy against viable cysts. 2. **Hymenolepis nana (Dwarf Tapeworm):** Praziquantel is the drug of choice. Unlike other tapeworms, a single dose of Niclosamide is often insufficient for *H. nana* due to its internal autoinfection cycle. 3. **Mechanism of Albendazole:** Inhibits microtubule synthesis by binding to β-tubulin. 4. **Vitamin Deficiency:** Diphyllobothrium latum (Fish tapeworm) is uniquely associated with **Vitamin B12 deficiency** (Megaloblastic anemia).

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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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