Infectious Diseases Practice Questions

Q: A 10-year-old child presents to the OPD with fever, neck rigidity, convulsions, and signs of meningeal irritation. Cerebrospinal fluid (CSF) examination shows normal glucose, slightly elevated proteins, and appears clear on gross examination. What is the most probable diagnosis?

Viral meningitis. ### Explanation The clinical presentation of fever, neck rigidity, and convulsions indicates **meningitis**. The key to differentiating the etiology lies in the **CSF analysis**. **1. Why Viral Meningitis is Correct:** Viral (Aseptic) meningitis typically presents with a **clear CSF appearance**. The biochemical markers are characteristic: * **Glucose:** Normal (Viruses do not consume glucose). * **Proteins:** Normal to slightly elevated (usually <100 mg/dL). * **Cell count:** Predominantly lymphocytic pleocytosis (though neutrophils may appear very early). The combination of meningeal signs with normal glucose and clear CSF is the classic "textbook" description of a viral etiology. **2. Why Other Options are Incorrect:** * **Bacterial Meningitis:** CSF is typically **turbid/purulent**. It shows **markedly low glucose** (hypoglycorrhachia), significantly elevated proteins, and a high polymorphonuclear (neutrophil) count. * **Tubercular Meningitis (TBM):** CSF is often clear or "cobweb" appearance. However, TBM is characterized by **very low glucose** and **very high protein** levels. The clinical course is usually more subacute/chronic compared to viral meningitis. * **Sub-arachnoid Hemorrhage:** While it causes signs of meningeal irritation (chemical meningitis), the CSF would be **grossly bloody or xanthochromic** (yellowish) rather than clear, with a high RBC count. **Clinical Pearls for NEET-PG:** * **Most common cause of viral meningitis:** Enteroviruses (Coxsackie, Echovirus). * **Mumps Meningitis:** Unique among viral causes as it can sometimes show *low* CSF glucose. * **CSF Glucose Rule:** Normal CSF glucose is approximately **2/3rd (60-70%)** of the simultaneous blood glucose level. * **Latex Agglutination Test:** Useful for rapid diagnosis of bacterial meningitis if the patient has already received prior antibiotics (partially treated meningitis).

Q: What is the most common complication of measles in children?

Otitis media. **Explanation:** Measles (Rubeola) is a highly contagious viral infection that leads to generalized immunosuppression, predisposing children to secondary bacterial infections. **Why Otitis Media is the correct answer:** While pneumonia is the most common cause of measles-related *death* in children, **Otitis Media** is statistically the **most common complication** overall. It occurs in approximately 5–10% of cases. The virus causes inflammation of the respiratory tract and Eustachian tube dysfunction, allowing secondary bacterial pathogens (like *S. pneumoniae*) to infect the middle ear. **Analysis of Incorrect Options:** * **A. Subacute sclerosing panencephalitis (SSPE):** This is a fatal, progressive degenerative neurological disorder. While it is a classic association, it is a **rare, late complication** occurring years after the initial infection (incidence ~1 in 10,000 to 100,000). * **B. Pulmonary hypertension:** This is not a recognized direct complication of measles. However, giant cell pneumonia (Hecht pneumonia) is a severe respiratory complication, especially in immunocompromised patients. * **D. Oophoritis:** This is a classic complication of **Mumps**, not Measles. **High-Yield Clinical Pearls for NEET-PG:** * **Most common complication:** Otitis Media. * **Most common cause of death:** Pneumonia. * **Most common neurological complication:** Post-measles encephalitis (Acute Disseminated Encephalomyelitis). * **Pathognomonic sign:** Koplik spots (found on the buccal mucosa opposite the lower 2nd molars). * **Vitamin Supplementation:** Vitamin A reduces morbidity and mortality in all children with acute measles. * **First sign of recovery:** Fading of the rash in the same order it appeared, often leaving behind "branny desquamation" and brownish staining.

Q: Subdural effusions in association with acute bacterial meningitis are:

A common occurrence. **Explanation:** Subdural effusion is a frequent complication of acute bacterial meningitis, particularly in infants. It occurs due to increased capillary permeability and the leakage of fluid into the potential space between the dura and the arachnoid mater during the inflammatory process. **Why Option D is Correct:** Studies indicate that subdural effusions occur in approximately **30–50% of infants** with bacterial meningitis (most commonly associated with *Streptococcus pneumoniae* and *Haemophilus influenzae* type b). Because they occur in nearly half of the cases, they are classified as a **common occurrence**. Most are asymptomatic and resolve spontaneously without intervention. **Why Other Options are Incorrect:** * **Option A:** Effusions are a physiological consequence of the inflammatory response to the infection itself, not a sign of antibiotic failure or inadequate treatment. * **Option B:** While subdural *hematomas* can be seen in bleeding disorders, subdural *effusions* (sterile fluid) are inflammatory in origin and not related to coagulopathies. * **Option C:** Most effusions are benign and asymptomatic. They are rarely fatal unless they become infected (subdural empyema) or cause significant mass effect leading to herniation, which is uncommon. **High-Yield Clinical Pearls for NEET-PG:** * **Most common organisms:** *S. pneumoniae* and *H. influenzae*. * **Clinical Signs:** Suspect effusion if there is a bulging fontanelle, rapidly increasing head circumference, or persistent fever despite 48–72 hours of appropriate antibiotics. * **Diagnosis:** Transillumination of the skull (in infants) or Neuroimaging (CT/MRI). * **Management:** Most require **observation only**. Surgical aspiration (subdural tap) is indicated only if there are signs of increased intracranial pressure (e.g., vomiting, seizures) or suspected empyema.

Q: A fetogram of a stillborn infant is shown below. What is the most likely diagnosis?

Congenital syphilis. ***Congenital syphilis*** - Characteristic **skeletal abnormalities** on fetogram include **periostitis**, **osteochondritis**, and **metaphyseal irregularities** affecting long bones. - **Wimberger sign** (bilateral destruction of the proximal medial tibial metaphysis) is pathognomonic for congenital syphilis on radiographic imaging. *Congenital varicella syndrome* - Primarily causes **limb defects**, **cortical atrophy**, and **cicatricial skin lesions** rather than distinctive bone changes. - Skeletal manifestations are typically **limb hypoplasia** and **shortened extremities**, not the periostitis seen in syphilis. *Congenital lupus* - Mainly presents with **cardiac conduction defects** (complete heart block) and **cutaneous manifestations** (neonatal lupus rash). - Does not typically cause the characteristic **bone lesions** or **periostitis** visible on fetogram imaging. *Congenital CMV infection* - Radiographic findings include **intracranial calcifications**, **microcephaly**, and **growth restriction** rather than bone abnormalities. - Skeletal involvement is rare and does not produce the **metaphyseal changes** and **periostitis** characteristic of syphilis.

Q: A 2-year-old boy presents in late summer with a 2-day history of painful, ulcerative lesions of the mouth and a 1-day history of fever up to 103°F. He refuses to eat. On examination, he is irritable with a temperature of 102°F and has numerous erythematous, ulcerative lesions on the buccal mucosa and tongue. What is the most likely diagnosis?

Herpetic gingivostomatitis. **Explanation:** **Herpetic Gingivostomatitis** is the most common manifestation of primary **Herpes Simplex Virus type 1 (HSV-1)** infection in children, typically occurring between ages 6 months and 5 years. **Why it is the correct answer:** The clinical presentation is classic: high-grade fever, irritability, and painful ulcerative lesions. Key diagnostic features include the involvement of the **buccal mucosa, tongue, and gingiva** (which often becomes friable and bleeds). The refusal to eat (odynophagia) due to pain is a hallmark sign. Unlike herpangina, which is seasonal, HSV can occur year-round, though it often presents with more severe systemic symptoms and anterior oral involvement. **Why the other options are incorrect:** * **Herpangina:** Caused by Coxsackievirus A. While it also presents with fever and ulcers, the lesions are typically localized to the **posterior pharynx** (soft palate, tonsillar pillars, and uvula), sparing the buccal mucosa and gingiva. * **Aphthous stomatitis:** These are "canker sores." They are usually recurrent, not associated with high-grade fever or systemic toxicity, and typically present as solitary or few ulcers rather than diffuse stomatitis. * **Candidal gingivostomatitis:** Oral thrush presents as white, curd-like plaques that can be scraped off, leaving an erythematous base. It is usually painless and rarely causes high fever unless associated with systemic immunodeficiency. **NEET-PG High-Yield Pearls:** * **Tzanck Smear:** Shows **multinucleated giant cells** and Cowdry type A inclusion bodies (diagnostic for HSV/VZV). * **Treatment:** Supportive care (hydration) is primary; oral **Acyclovir** is effective if started within 72 hours of onset. * **Complication:** Watch for **Dehydration** (most common) and **Herpetic Whitlow** (autoinoculation of the finger).

Q: Perinatal transmission of Hepatitis B is maximum when infection in the mother occurs in which period?

3rd trimester. **Explanation:** The risk of vertical transmission of Hepatitis B Virus (HBV) is directly proportional to the gestational age at which maternal infection occurs. **Why the 3rd Trimester is Correct:** The rate of transmission is highest (approximately **60–90%**) if the mother acquires acute Hepatitis B during the **third trimester** or the immediate postpartum period. This is primarily because the majority of perinatal transmission occurs during labor and delivery (peripartum) through contact with maternal blood and vaginal secretions. If the mother is acutely infected close to the time of delivery, her viral load is at its peak, and there is insufficient time for maternal antibodies to develop and provide passive protection to the fetus. **Analysis of Incorrect Options:** * **1st Trimester:** The risk of transmission is lowest here (approx. **10%**). While the virus can cross the placenta, it is less common early in pregnancy. * **2nd Trimester:** The risk is intermediate (approx. **25–30%**). * **Lactation:** Although HBV is present in breast milk, breastfeeding does not pose an additional risk of transmission to the infant, especially if the infant has received the HBV vaccine and Hepatitis B Immune Globulin (HBIG). **High-Yield Clinical Pearls for NEET-PG:** * **Most Common Route:** In endemic areas, the most common route of HBV transmission is **vertical (perinatal)**. * **Chronic Carrier State:** The younger the age of acquisition, the higher the risk of chronicity. Infants infected perinatally have a **90% risk** of becoming chronic carriers. * **HBeAg Status:** Transmission risk is highest (90%) if the mother is **HBeAg positive** (indicating high replication) and lower (10–20%) if she is HBeAg negative. * **Management:** To prevent transmission, the newborn must receive both the **HBV vaccine** and **HBIG** within 12 hours of birth.

Q: All are complications of diphtheria, except?

Hepatic failure. **Explanation:** Diphtheria is caused by *Corynebacterium diphtheriae*, which produces a potent **exotoxin** that inhibits protein synthesis (via ADP-ribosylation of Elongation Factor-2). While the bacteria remain localized to the upper respiratory tract (forming a pseudomembrane), the toxin spreads hematogenously, primarily affecting the heart, nervous system, and kidneys. **Why Hepatic Failure is the correct answer:** Hepatic failure is **not** a recognized complication of diphtheria. The toxin specifically targets tissues with high concentrations of receptors for the toxin, such as cardiac and neural tissues. While systemic toxemia can cause general malaise, the liver is not a primary target organ for the diphtheria toxin. **Analysis of other options:** * **Myocarditis (Option A):** This is the most common and most serious complication, occurring in about 10–25% of patients. It typically appears in the second week and is a leading cause of death. * **Ocular muscle palsy (Option B):** Neurological complications are common. **Cranial nerve palsies** (especially involving the soft palate, ciliary muscles causing blurring of vision, and extraocular muscles) typically occur in the 3rd to 5th week. * **Cerebellar ataxia (Option C):** While less common than peripheral neuropathy or palatal palsy, post-diphtheritic neurological involvement can rarely manifest as ataxia or encephalopathy due to the neurotoxic effects of the exotoxin. **NEET-PG High-Yield Pearls:** * **Most common cause of death:** Myocarditis. * **First sign of neurological involvement:** Palatal palsy (nasal twang/regurgitation). * **Treatment Priority:** Administer **Diphtheria Antitoxin (DAT)** immediately based on clinical suspicion; do not wait for culture results. * **Antibiotic of choice:** Erythromycin or Penicillin G (used to stop toxin production and prevent spread, but does not neutralize circulating toxin).

Question 1

DPT vaccine is contraindicated in which of the following conditions?

Accepted Answer

Evolving neurological illness

Answer

Family history of convulsions and neurological illness

Answer

Acute upper respiratory infection

Answer

Malnutrition

Question 2

A 10-year-old child presents to the OPD with fever, neck rigidity, convulsions, and signs of meningeal irritation. Cerebrospinal fluid (CSF) examination shows normal glucose, slightly elevated proteins, and appears clear on gross examination. What is the most probable diagnosis?

Accepted Answer

Viral meningitis

Answer

Bacterial meningitis

Answer

Tubercular meningitis

Answer

Sub-arachnoid hemorrhage

Question 3

What is the most common complication of measles in children?

Accepted Answer

Otitis media

Answer

Subacute sclerosing panencephalitis (SSPE)

Answer

Pulmonary hypertension

Answer

Oophoritis

Question 4

Which of the following is true about cerebral malaria in children?

Accepted Answer

Quinine is the drug of choice and hypoglycemia is a common complication.

Answer

Hypoglycemia is a common complication.

Answer

Cerebral malaria in children has a good prognosis.

Answer

Cerebral malaria is caused by Plasmodium vivax.

Question 5

Subdural effusions in association with acute bacterial meningitis are:

Accepted Answer

A common occurrence

Answer

The result of inadequate treatment

Answer

Indicative of a bleeding disorder

Answer

Usually fatal

Question 6

A fetogram of a stillborn infant is shown below. What is the most likely diagnosis?

Accepted Answer

Congenital syphilis

Answer

Congenital varicella syndrome

Answer

Congenital lupus

Answer

Congenital CMV infection

Question 7

A 2-year-old boy presents in late summer with a 2-day history of painful, ulcerative lesions of the mouth and a 1-day history of fever up to 103°F. He refuses to eat. On examination, he is irritable with a temperature of 102°F and has numerous erythematous, ulcerative lesions on the buccal mucosa and tongue. What is the most likely diagnosis?

Accepted Answer

Herpetic gingivostomatitis

Answer

Herpangina

Answer

Aphthous stomatitis

Answer

Candidal gingivostomatitis

Question 8

Perinatal transmission of Hepatitis B is maximum when infection in the mother occurs in which period?

Accepted Answer

3rd trimester

Answer

1st trimester

Answer

2nd trimester

Answer

Lactation

Question 9

A 3-year-old boy presents with a 1-day history of loose stools, fever, abdominal cramping, headache, and myalgia. He has no blood in the stool. A careful history reveals that he has several pet turtles. Which of the following is most likely the causative agent of his diarrhea?

Accepted Answer

Salmonella spp

Answer

Chlamydia psittaci

Answer

Entamoeba histolytica

Answer

Staphylococcus aureus

Question 10

All are complications of diphtheria, except?

Accepted Answer

Hepatic failure

Answer

Myocarditis

Answer

Ocular muscle palsy

Answer

Cerebellar ataxia

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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