Infectious Diseases Practice Questions

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

Toxoplasmosis. ### 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.

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

10-15 mg/kg/day. 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.

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

All of the above. **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).

Question 1

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 2

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 3

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 4

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 5

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 6

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

Accepted Answer

Toxoplasmosis

Answer

Congenital syphilis

Answer

Rubella

Answer

Herpes simplex

Question 7

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 8

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

Accepted Answer

10-15 mg/kg/day

Answer

15-20 mg/kg/day

Answer

20-25 mg/kg/day

Answer

5-10 mg/kg/day

Question 9

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

Accepted Answer

Henoch-Schonlein purpura

Answer

Thrombasthenia

Answer

Idiopathic thrombocytopenic purpura

Answer

Systemic Lupus Erythematosus

Question 10

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

Accepted Answer

All of the above

Answer

Albendazole

Answer

Niclosamide

Answer

Praziquantel

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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