Infectious Diseases Practice Questions

Q: What is the recommended single dose of Albendazole for a 10-year-old child being treated for roundworm infestation?

400 mg. **Explanation:** The correct answer is **400 mg (Option B)**. Albendazole is a broad-spectrum anthelmintic agent that works by inhibiting tubulin polymerization, leading to the metabolic disruption and death of the helminth. According to the World Health Organization (WHO) and the National Deworming Day (NDD) guidelines in India, the dosing for Albendazole in soil-transmitted helminth (STH) infections like *Ascaris lumbricoides* (roundworm) is age-dependent: * **Children aged 12–24 months:** 200 mg (half tablet) as a single dose. * **Children aged >24 months (2 years) to adults:** 400 mg (single tablet) as a single dose. Since the child in the question is 10 years old, the standard adult dose of 400 mg is indicated. **Analysis of Incorrect Options:** * **Option A (200 mg):** This is the recommended dose for children between 12 and 24 months of age. * **Options C and D (1 g and 2 g):** These doses are excessively high for a single treatment of roundworm and carry a significant risk of toxicity without added therapeutic benefit. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism of Action:** Binds to β-tubulin, inhibiting microtubule synthesis. * **Drug of Choice (DOC):** Albendazole is the DOC for Ascariasis, Hookworm, Enterobiasis (Pinworm), and Neurocysticercosis. * **Neurocysticercosis Dosing:** Unlike the single dose for worms, treatment for neurocysticercosis requires 15 mg/kg/day (max 800 mg) for 8–30 days, often co-administered with steroids to prevent inflammatory reactions. * **Contraindication:** Albendazole is generally avoided in the first trimester of pregnancy (teratogenic potential).

Q: 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?

Perform a blood monospot test and CBC. **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).

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

Conductive hearing loss. **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.

Q: 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?

IV Penicillin. ### 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.

Q: An 8-year-old child presents with acute lymphadenopathy and fever, with 20% lymphocytosis. What is the most likely diagnosis?

Infectious mononucleosis. ### Explanation The clinical presentation of acute fever, lymphadenopathy, and significant lymphocytosis in a child is a classic triad for **Infectious Mononucleosis (IM)**, most commonly caused by the Epstein-Barr Virus (EBV). **Why Option A is Correct:** Infectious mononucleosis typically presents with the "mononucleosis triad": fever, pharyngitis, and lymphadenopathy (usually posterior cervical). A key hematological hallmark is **absolute lymphocytosis** (often >50% of the total WBC count) with at least **10% atypical lymphocytes** (Downey cells). These atypical cells are actually activated T-lymphocytes reacting against EBV-infected B-cells. **Why Other Options are Incorrect:** * **Option B (ALL):** While ALL presents with lymphadenopathy and fever, the "lymphocytosis" in leukemia consists of **lymphoblasts** (immature cells), not mature atypical lymphocytes. Furthermore, ALL is usually associated with cytopenias (anemia, thrombocytopenia), which are absent here. * **Option C (Pulmonary TB):** TB typically presents with chronic (not acute) lymphadenopathy, night sweats, and weight loss. While it causes lymphocytosis, it does not typically present with the acute febrile syndrome described. * **Option D (Alpha-hemolytic Strep):** Bacterial infections usually cause **neutrophilia** with a "left shift" (increased band cells), rather than lymphocytosis. **NEET-PG High-Yield Pearls:** * **Diagnostic Test:** The **Monospot test** (Heterophile antibody test) is the initial screening test of choice. * **Atypical Lymphocytes:** Also seen in CMV, Toxoplasmosis, and Viral Hepatitis, but EBV is the most common cause. * **Clinical Caution:** Avoid prescribing **Ampicillin or Amoxicillin** in suspected IM, as it frequently causes a characteristic maculopapular rash. * **Complication:** Splenic rupture is a rare but serious complication; patients should avoid contact sports for 3–4 weeks.

Q: What is the commonest age group for infant botulism?

2 to 4 months. **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.

Q: What is the most common bacteria causing diarrhea in children?

Enteropathogenic E.coli. **Explanation:** Diarrhea remains a leading cause of morbidity and mortality in children worldwide. While **Rotavirus** is the most common *viral* cause, **Enteropathogenic E. coli (EPEC)** is recognized as the most common *bacterial* cause of diarrhea in children, particularly in infants and those in developing countries. **Why EPEC is the correct answer:** EPEC is a major cause of infantile diarrhea. It works through an "attachment and effacement" mechanism, where it adheres to intestinal epithelial cells using a bundle-forming pilus (bfp) and destroys the microvilli. This leads to malabsorption and watery diarrhea. It does not produce toxins, unlike other strains. **Analysis of Incorrect Options:** * **Enterotoxigenic E. coli (ETEC):** This is the most common cause of **Traveler’s diarrhea** in adults and children. It produces Heat-labile (LT) and Heat-stable (ST) toxins. * **Enteroinvasive E. coli (EIEC):** This strain invades the colonic mucosa, causing a syndrome similar to Shigellosis (dysentery with blood and mucus). It is less common than EPEC in the pediatric age group. * **Enterohemorrhagic E. coli (EHEC):** Specifically serotype O157:H7, it produces Shiga-like toxins. It is associated with **Hemolytic Uremic Syndrome (HUS)** and bloody diarrhea, but it is not the most common bacterial cause overall. **Clinical Pearls for NEET-PG:** * **Most common cause of diarrhea (Overall):** Rotavirus. * **Most common bacterial cause (Children):** EPEC. * **Most common bacterial cause (Adults/Travelers):** ETEC. * **Persistent Diarrhea in HIV:** Cryptosporidium parvum. * **Rice Water Stools:** Vibrio cholerae. * **Management Gold Standard:** Oral Rehydration Salts (ORS) and Zinc supplementation (20mg/day for 14 days; 10mg for infants <6 months).

Question 1

A 5-year-old girl presents with a several-day history of localized swelling in the right side of her neck. There is no recent history of sore throat. Physical examination reveals a low-grade fever and one very tender, firm, slightly enlarged lymph node in the right cervical region. A CBC shows mild leukocytosis, and fine needle aspiration of the lymph node reveals scattered neutrophils. Which of the following is the most likely diagnosis?

Accepted Answer

Bacterial lymphadenitis

Answer

Granulomatous lymphadenitis

Answer

Necrotizing lymphadenitis

Answer

Toxoplasmic lymphadenitis

Question 2

What is the recommended single dose of Albendazole for a 10-year-old child being treated for roundworm infestation?

Accepted Answer

400 mg

Answer

200 mg

Answer

1 g

Answer

2 g

Question 3

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?

Accepted Answer

Perform a blood monospot test and CBC

Answer

Start azithromycin

Answer

Check IgE for infectious mononucleosis

Answer

Presume Epstein-Barr virus infection and start acyclovir and prednisolone

Question 4

All of the following are true regarding congenital syphilis EXCEPT?

Accepted Answer

Conductive hearing loss

Answer

Rhinitis is an early sign

Answer

Notched incisors

Answer

Linear scars at the angle of mouth

Question 5

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?

Accepted Answer

IV Penicillin

Answer

IV Quinine

Answer

IV Artesunate

Answer

Chloroquine

Question 6

An 8-year-old child presents with acute lymphadenopathy and fever, with 20% lymphocytosis. What is the most likely diagnosis?

Accepted Answer

Infectious mononucleosis

Answer

Acute lymphoblastic leukemia (ALL)

Answer

Pulmonary tuberculosis (Koch's)

Answer

Alpha-hemolytic Streptococcal infection

Question 7

Which of the following statements regarding measles is false?

Accepted Answer

Koplik's spots cannot be seen in conjunctival or vaginal mucosa.

Answer

Vitamin A administration is part of the management of clinical measles.

Answer

CD 150 and PVRL4 are receptors for measles virus.

Answer

Pneumonia is the common cause of death in children with measles.

Question 8

What is the commonest age group for infant botulism?

Accepted Answer

2 to 4 months

Answer

1 to 3 weeks

Answer

10 to 12 months

Answer

7 to 9 months

Question 9

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

Accepted Answer

All of the above are indications for ART

Answer

Infants < 11 months with CD4 count < 1500 cells/mm³

Answer

Children 12-35 months with CD4 count < 500 cells/mm³

Answer

Children 36-59 months with CD4 count < 350 cells/mm³

Question 10

What is the most common bacteria causing diarrhea in children?

Accepted Answer

Enteropathogenic E.coli

Answer

Enterotoxigenic E.coli

Answer

Enteroinvasive E.coli

Answer

Enterohemorrhagic E.coli

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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