Infectious Diseases — MCQs

A 4-year-old child presented with fatigue, malaise, fever, sore throat, headache, nausea, abdominal pain, and myalgia. On examination, generalized lymphadenopathy and hepatosplenomegaly were noted. There was marked tonsillar enlargement along with palatal petechiae, rashes, and edema of the eyelids. A peripheral smear was performed, and the Paul Bunnel test was positive. All of the following can be caused by the organism responsible for these symptoms, except one?

Q270Medium

An 8-year-old child presents with crampy abdominal pain, nausea, and mild diarrhea for two weeks. The day before the visit, a cylindrical white worm, approximately 30 cm in length, was vomited and preserved. What is the most likely mode of acquisition for this organism?

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 261: Koplik spots on the buccal mucosa are typically seen in relation to which of the following teeth?

A. Incisors and canine
B. Canine and premolar
C. Only premolars
D. Premolar and molars (Correct Answer)

Explanation: **Explanation:** **Koplik spots** are the pathognomonic clinical sign of the **prodromal phase of Measles (Rubeola)**. They are small, irregular, bright red spots with a bluish-white speck in the center (often described as "grains of salt on a red background"). **Why Option D is Correct:** Koplik spots characteristically appear on the buccal mucosa opposite the **lower second molars**, though they can spread to involve the area opposite the **premolars** and other molars as the prodrome progresses. They typically appear 48 hours before the onset of the characteristic maculopapular rash and disappear within 48 hours of the rash appearing. **Why Other Options are Incorrect:** * **Options A & B:** While the spots can occasionally spread throughout the mouth in severe cases, their classic, diagnostic location is specifically the posterior buccal mucosa (molar region), not the anterior teeth like incisors or canines. * **Option C:** Restricting the location "only" to premolars is incorrect, as the most classic site described in medical literature is opposite the lower molars. **High-Yield Clinical Pearls for NEET-PG:** * **Timeline:** Koplik spots appear in the **prodromal stage** (pre-eruptive) and are usually gone by the 2nd day of the rash. * **Pathognomonic:** Their presence is diagnostic of Measles; no other viral exanthem presents with these specific lesions. * **Measles Triad (3 C’s):** Cough, Coryza, and Conjunctivitis precede the rash. * **Rash Progression:** The Measles rash is a maculopapular, blanching rash that starts **behind the ears** (retroauricular) and spreads cephalocaudally (head to toe). * **Vitamin A:** Supplementation is recommended for all children with Measles to reduce morbidity and mortality.

Question 262: What is the most common bacteria causing diarrhea in children?

A. Enterotoxigenic E.coli
B. Enteroinvasive E.coli
C. Enterohemorrhagic E.coli
D. Enteropathogenic E.coli (Correct Answer)

Explanation: **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 263: A 2-year-old girl presents with recurrent episodes of diarrhea (mucus and blood at times), hepatosplenomegaly, perianal excoriation, and resistant oral thrush. She weighs 6 kg and measures 78 cm in height. What is the most likely diagnosis?

A. Necrotizing enterocolitis
B. Lactose intolerance
C. HIV infection (Correct Answer)
D. Campylobacter jejuni infection

Explanation: ### Explanation The clinical presentation of this 2-year-old girl is highly suggestive of **Pediatric HIV infection**. The diagnosis is based on a constellation of chronic, multi-systemic findings: 1. **Failure to Thrive (FTT):** Her weight (6 kg) is significantly low for her age and height (78 cm), indicating severe wasting. 2. **Opportunistic & Recurrent Infections:** Resistant oral thrush (Candidiasis) and chronic/recurrent diarrhea (often due to *Cryptosporidium* or *Isospora*) are hallmark signs of immunodeficiency. 3. **Physical Findings:** Hepatosplenomegaly and perianal excoriation (secondary to chronic diarrhea) are common clinical markers in pediatric HIV. **Analysis of Incorrect Options:** * **A. Necrotizing enterocolitis:** Typically occurs in preterm neonates in the first few weeks of life, presenting with abdominal distension and pneumatosis intestinalis, not chronic FTT and thrush. * **B. Lactose intolerance:** While it causes osmotic diarrhea and perianal excoriation, it does not explain hepatosplenomegaly, resistant thrush, or severe systemic wasting. * **D. Campylobacter jejuni:** Causes acute bloody diarrhea (dysentery), but it is a self-limiting or acute bacterial infection and doesn't account for the chronic multi-organ involvement. **NEET-PG High-Yield Pearls:** * **Cardinal Signs:** Suspect HIV in children with "The Triad": Chronic diarrhea, Failure to Thrive, and Persistent Lymphadenopathy/Hepatosplenomegaly. * **Diagnosis:** In children **<18 months**, diagnosis is via **HIV DNA PCR** (due to persistence of maternal antibodies). In children **>18 months**, **ELISA** is used. * **Most Common Opportunistic Infection:** *Pneumocystis jirovecii* pneumonia (PCP) is the most common opportunistic infection in HIV-infected infants, peaking between 3–6 months of age. * **WHO Clinical Staging:** Oral candidiasis and unexplained persistent diarrhea for >1 month place the child in Clinical Stage 3 or 4.

Question 264: Which of the following does not establish a diagnosis of congenital Cytomegalovirus (CMV) infection in a neonate?

A. Urine culture for CMV
B. IgG CMV antibodies in blood (Correct Answer)
C. Intranuclear inclusion bodies in hepatocytes
D. CMV viral DNA in blood by polymerase chain reaction

Explanation: To establish a diagnosis of **congenital Cytomegalovirus (CMV)** infection, the virus or its components must be identified within the **first 3 weeks of life**. ### **Why Option B is the Correct Answer** **IgG CMV antibodies** in a neonate’s blood do not confirm congenital infection because IgG antibodies cross the placenta from the mother to the fetus (passive immunity). Therefore, a positive IgG test in a newborn may simply reflect maternal past infection rather than an active fetal infection. To diagnose congenital CMV via serology, one would need to detect **CMV-specific IgM**, which does not cross the placenta. ### **Analysis of Incorrect Options** * **A. Urine culture:** This was traditionally the "gold standard." CMV is shed in high titers in the urine of infected neonates. * **C. Intranuclear inclusion bodies:** Histopathological identification of characteristic **"Owl’s eye" inclusion bodies** in tissues (like hepatocytes or renal tubular cells) is pathognomonic for CMV. * **D. PCR for viral DNA:** This is the current preferred diagnostic method due to its high sensitivity and rapid results. It can be performed on blood, urine, or saliva. ### **NEET-PG High-Yield Pearls** * **Timing is Critical:** Testing must be done within **21 days of birth**. Detection after 3 weeks may represent *acquired* (perinatal) infection rather than *congenital*. * **Most Common Cause:** CMV is the most common cause of **congenital sensorineural hearing loss (SNHL)** and non-hereditary mental retardation. * **Classic Triad:** Periventricular calcifications, microcephaly, and SNHL. * **Treatment:** Intravenous **Ganciclovir** or oral **Valganciclovir** is indicated for symptomatic neonates to reduce the severity of hearing loss and developmental delay.

Question 265: What is a known side effect of the pertussis vaccine?

A. Local pain
B. Excessive cry
C. Fever
D. All of the above (Correct Answer)

Explanation: **Explanation:** The pertussis vaccine, particularly the **Whole-cell Pertussis (wP)** component traditionally used in the DTP (Diphtheria, Tetanus, Pertussis) vaccine, is highly immunogenic but also associated with a high frequency of reactogenicity. These reactions occur because the whole-cell vaccine contains inactivated *Bordetella pertussis* bacteria with multiple antigens and endotoxins. **Breakdown of Side Effects:** * **Local pain (Option A):** This is the most common reaction, occurring in about 50% of recipients. It presents as redness, swelling, and tenderness at the injection site. * **Excessive cry (Option B):** Persistent, inconsolable crying (lasting >3 hours) is a specific systemic reaction to the pertussis component, seen in approximately 1% of children. * **Fever (Option C):** Mild to moderate fever is a frequent systemic response as the body mounts an immune reaction. Since all three symptoms are documented side effects of the pertussis vaccine, **Option D (All of the above)** is the correct answer. **High-Yield NEET-PG Pearls:** 1. **Acellular Pertussis (aP):** To reduce these side effects, the acellular vaccine (DTaP) was developed. It contains only specific purified antigens (like pertussis toxin) and has significantly lower rates of fever and local reactions compared to DTwP. 2. **Neurological Complications:** Rare but serious side effects include **febrile seizures** and **hypotonic-hyporesponsive episodes (HHE)**. 3. **Contraindication:** An immediate anaphylactic reaction or **encephalopathy** within 7 days of a previous dose is an absolute contraindication to further pertussis vaccination. 4. **Shift in Practice:** While developed nations use DTaP, many national programs (like India's UIP) still use DTwP because it is more cost-effective and provides a more robust primary immune response.

Question 266: What is the most common complication of malaria in children?

A. Cerebral malaria
B. Respiratory distress
C. Severe malarial anemia (Correct Answer)
D. Hypoglycemia

Explanation: **Explanation:** In pediatric populations, particularly in high-transmission areas (Sub-Saharan Africa and parts of SE Asia), **Severe Malarial Anemia (SMA)** is the most frequent manifestation of severe *Plasmodium falciparum* infection. **Why Severe Malarial Anemia is the correct answer:** The pathogenesis involves a triad of: 1. **Direct Parasitization:** Destruction of infected RBCs during schizogony. 2. **Splenic Sequestration:** Removal of both infected and non-infected RBCs by the spleen. 3. **Dyserythropoiesis:** Bone marrow suppression mediated by inflammatory cytokines (TNF-α), which inhibits the production of new RBCs. In children, who have lower iron stores and higher growth demands, this leads to a rapid and profound drop in hemoglobin. **Analysis of Incorrect Options:** * **Cerebral Malaria (A):** While it is the most common cause of **death** and the most dramatic presentation, it is statistically less frequent than anemia in children. * **Respiratory Distress (B):** Often caused by metabolic acidosis (Kussmaul breathing) or pulmonary edema, it is a significant predictor of mortality but occurs less frequently than SMA. * **Hypoglycemia (D):** A common metabolic complication due to parasite glucose consumption and quinine therapy, but it is secondary to the hematological impact. **NEET-PG High-Yield Pearls:** * **Most common complication in children:** Severe Malarial Anemia. * **Most common complication in adults:** Acute Renal Failure (ARF) and Jaundice. * **Most common cause of death (overall):** Cerebral Malaria. * **WHO Definition of SMA:** Hemoglobin < 5 g/dL or Hematocrit < 15% in the presence of parasitemia. * **Drug of Choice for Severe Malaria:** Intravenous Artesunate (preferred over Quinine).

Question 267: An 18-month-old child weighing 11.5 kg presents to the primary health center with fever and respiratory difficulty. On examination, the child is lethargic, with a respiratory rate of 46 bpm and no chest retractions. What is the most appropriate management of this child?

A. Prescribe oral antibiotics, warn of danger signs and send home (Correct Answer)
B. Intravenous fluids alone
C. Intravenous antibiotics and observation
D. Give intravenous antibiotics and refer to a higher center

Explanation: ### Explanation This question tests the application of the **IMNCI (Integrated Management of Neonatal and Childhood Illness)** guidelines for the classification and management of acute respiratory infections. **1. Why Option A is Correct:** The child’s classification is based on age-specific respiratory rates. For a child aged 12 months to 5 years, a respiratory rate of **≥40 breaths per minute (bpm)** is defined as **fast breathing**. * **Assessment:** The child has fast breathing (46 bpm) but **no chest indrawing** and **no general danger signs** (the "lethargy" mentioned must be interpreted in the context of fever; however, if a child is truly lethargic/unconscious, it becomes "Very Severe Disease." In standard NEET-PG vignettes, if no stridor or chest indrawing is present, it is classified as **Pneumonia**). * **Management of Pneumonia:** According to IMNCI, children with "Pneumonia" (fast breathing only) should be treated with **oral Amoxicillin** (40 mg/kg/day in two divided doses) for 5 days, advised on home care, and told when to return immediately (danger signs). **2. Why Other Options are Wrong:** * **Options C & D:** These are reserved for **"Severe Pneumonia or Very Severe Disease,"** characterized by chest indrawing, stridor in a calm child, or general danger signs (inability to drink, persistent vomiting, convulsions, or true lethargy/unconsciousness). This child lacks chest retractions. * **Option B:** IV fluids alone are never the primary treatment for pneumonia and are only supportive in severe cases. **3. Clinical Pearls for NEET-PG:** * **IMNCI Cut-offs for Fast Breathing:** * <2 months: ≥60 bpm * 2–12 months: ≥50 bpm * 12 months–5 years: ≥40 bpm * **Drug of Choice:** Oral Amoxicillin is now the first-line treatment for non-severe pneumonia in the community setting, replacing oral Cotrimoxazole. * **Danger Signs:** Always look for "Chest Indrawing"—it is the key differentiator between Pneumonia and Severe Pneumonia.

Question 268: Koplik spots are described as:

A. The first manifestation of measles.
B. Rarely seen in measles.
C. Seen 2-3 days after cutaneous rashes.
D. A manifestation seen before cutaneous rashes but seldom observed. (Correct Answer)

Explanation: **Explanation:** **Koplik spots** are the pathognomonic enanthem of Measles (Rubeola). They are described as small, bluish-white grains of sand on an erythematous base, typically found on the buccal mucosa opposite the lower second molars. 1. **Why Option D is Correct:** Koplik spots appear during the **prodromal stage**, usually 48 hours before the onset of the characteristic maculopapular rash. While they are highly specific for measles, they are "seldom observed" in clinical practice because they are transient, appearing and disappearing within 12–24 hours, often before the patient seeks medical attention for the rash. 2. **Why Other Options are Incorrect:** * **Option A:** The first manifestations of measles are the "3 Cs"—Cough, Coryza, and Conjunctivitis—along with high-grade fever. Koplik spots follow these initial symptoms. * **Option B:** They are not "rarely seen" in terms of occurrence (they occur in up to 70-90% of cases); they are simply missed due to their fleeting nature. * **Option C:** Koplik spots precede the rash. They typically start to fade as the cutaneous rash begins to appear. **High-Yield Clinical Pearls for NEET-PG:** * **Pathognomonic:** Koplik spots = Measles. * **Timeline:** Prodromal stage (Day 2-3) → Koplik spots → Exanthematous stage (Day 4: Rash starts behind ears). * **Vitamin A:** Supplementation is recommended for all children with measles to reduce morbidity and mortality. * **SSPE:** Subacute Sclerosing Panencephalitis is a late, lethal neurological complication of measles occurring years later. * **Modified Measles:** Occurs in partially immune individuals; Koplik spots are usually absent here.

Question 269: A 4-year-old child presented with fatigue, malaise, fever, sore throat, headache, nausea, abdominal pain, and myalgia. On examination, generalized lymphadenopathy and hepatosplenomegaly were noted. There was marked tonsillar enlargement along with palatal petechiae, rashes, and edema of the eyelids. A peripheral smear was performed, and the Paul Bunnel test was positive. All of the following can be caused by the organism responsible for these symptoms, except one?

A. Nasopharyngeal carcinoma
B. Non-Hodgkin lymphoma
C. Diffuse gastric carcinoma
D. Primary effusion lymphoma (Correct Answer)

Explanation: ### Explanation **Diagnosis:** The clinical presentation of fever, sore throat, generalized lymphadenopathy, hepatosplenomegaly, and palatal petechiae, combined with a positive **Paul Bunnel test** and atypical lymphocytosis on peripheral smear, confirms a diagnosis of **Infectious Mononucleosis** caused by the **Epstein-Barr Virus (EBV)**. **Why Option D is Correct:** **Primary Effusion Lymphoma (PEL)** is a rare B-cell lymphoma primarily associated with **Human Herpesvirus 8 (HHV-8)**, also known as Kaposi Sarcoma-associated Herpesvirus (KSHV). While EBV can be a co-infector in PEL, HHV-8 is the definitive causative agent. **Why Other Options are Incorrect:** EBV is a potent oncogenic virus associated with several malignancies due to its ability to immortalize B-cells and epithelial cells: * **A. Nasopharyngeal Carcinoma:** Strongly associated with EBV, particularly the undifferentiated type (Type 3), common in Southern China and parts of Africa. * **B. Non-Hodgkin Lymphoma (NHL):** EBV is linked to several NHL subtypes, most notably **Burkitt Lymphoma** (endemic form), Hodgkin Lymphoma (mixed cellularity), and B-cell lymphomas in immunocompromised patients. * **C. Diffuse Gastric Carcinoma:** Approximately 10% of gastric adenocarcinomas worldwide are associated with EBV. **Clinical Pearls for NEET-PG:** * **Classic Triad of IM:** Fever, Pharyngitis, and Lymphadenopathy (usually posterior cervical). * **The "Ampicillin Rash":** If a patient with IM is mistakenly treated with Ampicillin or Amoxicillin, a characteristic maculopapular rash often develops. * **Hematology:** Look for **Downey cells** (atypical T-lymphocytes) on peripheral smear. * **Hoagland Sign:** Early transient upper eyelid edema seen in Infectious Mononucleosis. * **Splenic Rupture:** A rare but life-threatening complication; patients are advised to avoid contact sports for 3–4 weeks.

Question 270: An 8-year-old child presents with crampy abdominal pain, nausea, and mild diarrhea for two weeks. The day before the visit, a cylindrical white worm, approximately 30 cm in length, was vomited and preserved. What is the most likely mode of acquisition for this organism?

A. Autoinfection
B. Ingestion of cysts in contaminated water
C. Ingestion of eggs from an infected pet
D. Ingestion of eggs from human feces (Correct Answer)

Explanation: **Explanation:** The clinical presentation of a large (30 cm), cylindrical white worm being vomited is pathognomonic for **Ascaris lumbricoides** (Giant Roundworm). Ascariasis is the most common helminthic infection worldwide. **1. Why Option D is Correct:** *Ascaris lumbricoides* is a soil-transmitted helminth. The life cycle begins when an infected human defecates in the soil. The eggs must undergo a period of maturation (embryonation) in the soil for 2–3 weeks to become infective. Humans acquire the infection via the **fecal-oral route** by ingesting these embryonated eggs from contaminated soil, food, or water. Since humans are the only reservoir, the eggs originate from human feces. **2. Why Other Options are Incorrect:** * **Option A (Autoinfection):** This is characteristic of *Strongyloides stercoralis* or *Enterobius vermicularis*. *Ascaris* eggs require time in the soil to become infective and cannot cause immediate autoinfection. * **Option B (Ingestion of cysts):** This is the mode of transmission for protozoa like *Giardia lamblia* or *Entamoeba histolytica*, not large nematodes. * **Option C (Infected pet):** While *Toxocara canis* (dog roundworm) is acquired from pets, it causes Visceral Larva Migrans in humans; the adult worms do not develop in the human intestine and are not vomited. **Clinical Pearls for NEET-PG:** * **Löffler Syndrome:** Pulmonary phase of *Ascaris* migration characterized by eosinophilic pneumonia, cough, and wheezing. * **Complications:** Intestinal obstruction (at the ileocecal valve), biliary colic, or pancreatitis due to worm migration. * **Diagnosis:** Stool microscopy for bile-stained, mamillated eggs. * **Treatment:** Albendazole (400 mg single dose) is the drug of choice.

Practice by Chapter

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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