Infectious Diseases — MCQs

A previously healthy 18-month-old girl is brought to the office with 2 days of irritability, poor appetite, and pulling at her left ear. She has no known allergies, and her temperature is 102.8 F. She is easily consoled by the mother and moves her neck spontaneously without discomfort. There is a clear discharge from the nares. The left tympanic membrane is erythematous, dull, and bulging. Which of the following virulence factors is generally absent in the strains of the causative organism that produce otitis media, compared with those that produce epiglottitis or meningitis?

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 151: Unilateral sensorineural hearing loss may occur in which of the following infections?

A. Coronavirus
B. Pertussis
C. Rotavirus
D. Mumps (Correct Answer)

Explanation: **Explanation:** **Mumps** is the correct answer because it is a well-known cause of sudden-onset **unilateral sensorineural hearing loss (SNHL)**. The virus causes endolymphatic labyrinthitis, leading to the destruction of the hair cells in the organ of Corti. While parotitis is the most common clinical feature of Mumps, deafness is a significant, though rare (approx. 1 in 20,000 cases), permanent complication. It is typically sudden in onset and most frequently unilateral, though bilateral involvement can occur. **Incorrect Options:** * **Coronavirus:** While COVID-19 has been associated with various neurological symptoms and occasional reports of hearing loss, it is not a classic or high-yield association in pediatric infectious diseases compared to Mumps. * **Pertussis:** Caused by *Bordetella pertussis*, this primarily affects the respiratory system (whooping cough). Complications are usually pulmonary (pneumonia) or neurological due to hypoxia (encephalopathy/seizures), not SNHL. * **Rotavirus:** This is a leading cause of viral gastroenteritis in children. Its complications are related to dehydration and electrolyte imbalances, not auditory nerve damage. **Clinical Pearls for NEET-PG:** * **Mumps** is the most common cause of **unilateral** acquired SNHL in children. * **Measles** is a more common cause of **bilateral** acquired SNHL. * Other classic causes of SNHL in pediatrics include **Congenital CMV** (most common non-syndromic cause) and **Meningitis** (specifically *S. pneumoniae*). * Remember the "Mumps Complications" mnemonic: **O**rchitis (most common post-pubertal), **P**ancreatitis, **E**ncephalitis, and **D**eafness.

Question 152: Which of the following sexually transmitted diseases can cause fetal abnormalities?

A. Herpes simplex virus
B. Hepatitis B virus
C. Neisseria gonorrhoeae
D. Treponema pallidum (Correct Answer)

Explanation: **Explanation:** The correct answer is **Treponema pallidum**, the causative agent of **Syphilis**. This organism is unique among the options because it can cross the placental barrier (transplacental transmission) as early as the 9th week of gestation, leading to **Congenital Syphilis**. This condition is characterized by significant fetal abnormalities and multisystem involvement. * **Treponema pallidum (Correct):** It causes classic fetal abnormalities categorized into early and late manifestations. High-yield findings include **Hutchinson’s triad** (interstitial keratitis, sensorineural hearing loss, and notched incisors), **Saddle nose** deformity, **Saber shins**, and **Mulberry molars**. It can also lead to hydrops fetalis or intrauterine growth restriction (IUGR). * **Herpes simplex virus (Incorrect):** While HSV can be transmitted to the neonate, it typically occurs **during delivery** (intrapartum) via contact with infected vaginal secretions. It causes neonatal herpes (skin-eye-mouth disease, encephalitis, or disseminated disease) rather than structural fetal abnormalities. * **Hepatitis B virus (Incorrect):** Transmission is usually vertical (during birth). It does not cause structural malformations; instead, it puts the infant at a high risk of becoming a **chronic carrier**, leading to potential cirrhosis or hepatocellular carcinoma later in life. * **Neisseria gonorrhoeae (Incorrect):** Transmission occurs during birth. The primary clinical manifestation is **Ophthalmia neonatorum** (purulent conjunctivitis), not congenital malformations. **NEET-PG Clinical Pearls:** * **Screening:** All pregnant women are screened for Syphilis using VDRL/RPR. * **Treatment:** Penicillin G is the only effective treatment to prevent fetal transmission; if the mother is allergic, she must be **desensitized** and then treated with Penicillin. * **Radiology:** Look for **Wimberger’s sign** (localized bilateral metaphyseal destruction of the proximal tibia) on X-ray, which is pathognomonic for congenital syphilis.

Question 153: What is the correct indication for prophylaxis with varicella-zoster immunoglobulin in chicken-pox?

A. Should be given within 24 hours of exposure
B. Given to a newborn contact (Correct Answer)
C. Can be given concurrently with the varicella vaccine
D. Administered in established chicken-pox disease

Explanation: **Explanation:** The primary goal of **Varicella-Zoster Immunoglobulin (VZIG)** is to provide passive immunity to high-risk individuals who have been exposed to the virus but cannot mount an effective immune response or are at risk of severe complications. **Why Option B is Correct:** Neonates are at high risk for **Neonatal Varicella**, a potentially fatal condition. VZIG is specifically indicated for newborns if the mother develops chickenpox within **5 days before to 2 days after delivery**. In this window, the mother develops viremia but hasn't had enough time to transfer protective IgG antibodies to the fetus, leaving the newborn vulnerable. **Analysis of Incorrect Options:** * **Option A:** While VZIG should be given as soon as possible, the window for administration is up to **96 hours (4 days)** post-exposure (some guidelines extend this to 10 days), not strictly limited to 24 hours. * **Option C:** VZIG and the Varicella vaccine should **not** be given concurrently. Passive antibodies in VZIG can interfere with the replication of the live-attenuated virus in the vaccine, rendering it ineffective. If both are needed, they must be spaced apart. * **Option D:** VZIG is for **prophylaxis**, not treatment. Once the disease is established (rash appears), VZIG is ineffective; antiviral therapy (Acyclovir) is the treatment of choice for severe cases. **High-Yield Clinical Pearls for NEET-PG:** * **Indications for VZIG:** Immunocompromised individuals, pregnant women without immunity, and specific neonates (as described above). * **Post-exposure Prophylaxis (PEP):** In healthy susceptible children >12 months, the **Varicella Vaccine** is the preferred PEP if given within 3–5 days of exposure. * **Congenital Varicella Syndrome:** Occurs if the mother is infected in the first 20 weeks of pregnancy (presents with cicatricial skin scars, limb hypoplasia, and microcephaly).

Question 154: What is a common complication of chickenpox in children?

A. Encephalitis
B. Secondary bacterial infection (Correct Answer)
C. Pneumonia
D. Otitis media

Explanation: **Explanation:** **1. Why Secondary Bacterial Infection is Correct:** Secondary bacterial infection of the skin (typically by *Staphylococcus aureus* or *Streptococcus pyogenes*) is the **most common complication** of chickenpox in children. The intense pruritus (itching) associated with the vesicular rash leads to scratching, which compromises the skin barrier and allows for bacterial inoculation. This can manifest as impetigo, cellulitis, or even necrotizing fasciitis. **2. Analysis of Incorrect Options:** * **A. Encephalitis:** While a serious neurological complication, it is rare. In children, the most common neurological manifestation is **Acute Cerebellar Ataxia**, which presents with a sudden onset of gait instability. * **C. Pneumonia:** Varicella pneumonia is the **most common complication in adults** and pregnant women, but it is relatively rare in healthy children. It is often severe and carries a high mortality rate in immunocompromised patients. * **D. Otitis media:** While it can occur following viral prodromes, it is not a classic or frequent complication specifically associated with the Varicella-zoster virus. **3. NEET-PG High-Yield Pearls:** * **Infectivity:** Patients are infectious from **1–2 days before** the rash appears until **all lesions have crusted over**. * **Congenital Varicella Syndrome:** Occurs if the mother is infected between 8–20 weeks of gestation; characterized by cicatricial skin scarring, limb hypoplasia, and microcephaly. * **Reye Syndrome:** A historical complication associated with **aspirin** use during chickenpox; hence, paracetamol is the preferred antipyretic. * **Treatment:** Oral Acyclovir is not routinely recommended for healthy children under 12 but is indicated for adolescents, adults, and those with chronic skin/lung diseases.

Question 155: A rash with retro-auricular origin is typically seen in which of the following conditions?

A. Rubella
B. Rubeola (Correct Answer)
C. Chickenpox
D. Mumps

Explanation: **Explanation:** The correct answer is **Rubeola (Measles)**. In Rubeola, the characteristic maculopapular rash typically appears on the 4th day of fever. It follows a classic **cephalocaudal progression**, starting behind the ears (**retro-auricular**) and along the hairline, then spreading downwards to the face, neck, trunk, and finally the extremities. This specific anatomical starting point is a hallmark clinical feature used to differentiate it from other exanthematous illnesses. **Analysis of Options:** * **Rubella (German Measles):** While the rash also starts on the face and spreads downwards, it is typically lighter (pinkish), non-confluent, and disappears much faster ("3-day measles"). The most characteristic feature of Rubella is **post-auricular and suboccipital lymphadenopathy**, rather than just the rash origin. * **Chickenpox (Varicella):** The rash typically starts on the **trunk** (centripetal distribution) and is pleomorphic (macules, papules, vesicles, and crusts present simultaneously). * **Mumps:** This is a viral infection primarily affecting the parotid glands. It presents with **parotid swelling** and does not typically present with a generalized maculopapular rash. **High-Yield Clinical Pearls for NEET-PG:** * **Koplik Spots:** Pathognomonic for Measles; seen on the buccal mucosa opposite the lower 2nd molars *before* the rash appears. * **Vitamin A:** Supplementation is mandatory in Measles management to reduce morbidity and mortality. * **Complications:** The most common complication is Otitis Media; the most common cause of death is Pneumonia; the most dreaded late complication is SSPE (Subacute Sclerosing Panencephalitis). * **Infectivity:** Measles is most infectious during the prodromal (catarrhal) stage.

Question 156: Which of the following is FALSE regarding Poliomyelitis?

A. Descending paralysis
B. Bilateral and symmetrical involvement (Correct Answer)
C. Non-progressive condition
D. Lower Motor Neuron (LMN) type paralysis

Explanation: **Explanation:** Poliomyelitis is an acute viral infection caused by the Poliovirus (an enterovirus), primarily affecting the anterior horn cells of the spinal cord. **Why Option B is the Correct (False) Statement:** The hallmark of paralytic poliomyelitis is **asymmetrical** and **random** involvement of muscles. It typically affects one limb more than the other (most commonly the legs) and rarely presents with perfect symmetry. If a patient presents with acute flaccid paralysis that is bilateral and symmetrical, clinicians should prioritize a diagnosis of Guillain-Barré Syndrome (GBS) over Polio. **Analysis of Other Options:** * **Option A (Descending paralysis):** While Polio is often described as affecting proximal muscles more than distal ones, the paralysis characteristically spreads in a **descending** fashion (starting from the hip/shoulder and moving downwards). * **Option C (Non-progressive condition):** Once the febrile illness subsides and the paralysis is established (usually within 48–72 hours), the paralysis is **static and non-progressive**. Any further "progression" after the fever touches baseline is unlikely to be Polio. * **Option D (LMN type paralysis):** Because the virus destroys the **anterior horn cells** (the final common pathway of the motor system), it results in classic **Lower Motor Neuron (LMN)** signs: flaccidity, loss of deep tendon reflexes, and eventual muscle atrophy. **High-Yield Clinical Pearls for NEET-PG:** * **Most common presentation:** Asymptomatic/Inapparent infection (>90-95%). * **CSF Findings:** Albuminocytologic dissociation is **absent** (unlike GBS). There is initial pleocytosis. * **Diagnosis:** Isolation of the virus from **stool samples** (two samples collected 24 hours apart) is the gold standard for AFP surveillance. * **Prognosis:** Maximum recovery occurs within the first 6 months; paralysis persisting beyond 60 days is usually permanent.

Question 157: In children, infantile diarrhea is most commonly due to which of the following?

A. Adenovirus
B. Rotavirus (Correct Answer)
C. Reovirus
D. HPV

Explanation: **Explanation:** **Rotavirus** is the most common cause of severe, dehydrating diarrhea in infants and young children worldwide. It primarily affects the **6 to 24-month age group**, as infants younger than 6 months often have passive immunity from maternal antibodies. The virus infects the mature enterocytes of the small intestine, leading to malabsorption and osmotic diarrhea. It also produces a viral enterotoxin, **NSP4**, which induces secretory diarrhea by increasing intracellular calcium. **Analysis of Options:** * **Adenovirus (Option A):** Specifically Serotypes 40 and 41 (Enteric Adenoviruses) are the second most common cause of viral gastroenteritis in children, but they occur less frequently than Rotavirus. * **Reovirus (Option C):** While Rotavirus belongs to the *Reoviridae* family, the term "Reovirus" usually refers to Respiratory Enteric Orphan viruses, which are rarely associated with significant clinical disease in humans. * **HPV (Option D):** Human Papillomavirus is associated with skin warts and mucosal lesions (e.g., cervical cancer) and is not a cause of gastroenteritis. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Causes "patchy mucosal injury" and produces the enterotoxin **NSP4**. * **Seasonality:** Peak incidence occurs in **winter months** (often called "winter diarrhea"). * **Diagnosis:** The gold standard for rapid detection is **ELISA** or Latex Agglutination for viral antigen in stools. * **Vaccination:** Live attenuated oral vaccines (Rotarix, RotaTeq, and Rotavac) are part of the Universal Immunization Programme (UIP) in India to reduce infant mortality. * **Management:** The mainstay of treatment is **ORS and Zinc supplementation** (20mg/day for 14 days) to reduce the duration and severity.

Question 158: A 4-year-old boy presents with a history of bloody diarrhea and is now hospitalized for oliguria and hypertension. With which organism is he most likely infected?

A. Clostridium perfringens
B. Salmonella typhi
C. Enteroinvasive E. coli
D. Shiga toxin-producing E. coli (Correct Answer)

Explanation: ### Explanation The clinical presentation of **bloody diarrhea** followed by **oliguria** (decreased urine output) and **hypertension** in a child is a classic triad for **Hemolytic Uremic Syndrome (HUS)**. **1. Why the Correct Answer is Right:** The most common cause of HUS in children is **Shiga toxin-producing E. coli (STEC)**, specifically the **O157:H7** serotype. The Shiga toxin enters the bloodstream and causes endothelial damage, primarily in the glomerular capillaries. This leads to: * **Microangiopathic Hemolytic Anemia (MAHA):** Fragmented RBCs (schistocytes). * **Thrombocytopenia:** Platelet consumption in microthrombi. * **Acute Kidney Injury (AKI):** Presenting as oliguria, hypertension, and uremia. **2. Why the Other Options are Incorrect:** * **Clostridium perfringens:** Typically causes watery diarrhea or gas gangrene; it is not associated with HUS or renal failure. * **Salmonella typhi:** Causes Enteric Fever (high fever, bradycardia, rose spots, and hepatosplenomegaly). While it can cause intestinal perforation, it does not typically cause HUS. * **Enteroinvasive E. coli (EIEC):** Causes a dysentery-like illness similar to Shigellosis by invading the colonic mucosa, but it does not produce the Shiga toxin required to trigger HUS. **3. High-Yield Clinical Pearls for NEET-PG:** * **HUS Triad:** Microangiopathic hemolytic anemia (Schistocytes on peripheral smear), Thrombocytopenia, and Acute Renal Failure. * **Management:** Primarily supportive (fluid/electrolyte balance, dialysis if needed). **Antibiotics are generally avoided** in STEC infections as they may increase toxin release and worsen the risk of HUS. * **Most common cause of AKI in children:** HUS is a leading cause of acquired acute renal failure in the pediatric population.

Question 159: A 1-year-old girl presents with a 3-day history of fever and diarrhea. Her temperature is 38°C (101°F), and her CBC shows a normal white blood cell count and increased hematocrit. Which of the following microorganisms is the most likely cause of diarrhea in this child?

A. Cytomegalovirus
B. Rotavirus (Correct Answer)
C. Salmonella typhi
D. Shigella dysenteriae

Explanation: **Explanation:** The clinical presentation of a 1-year-old child with fever and watery diarrhea, accompanied by signs of dehydration (increased hematocrit), is classic for **Rotavirus** infection. **1. Why Rotavirus is correct:** Rotavirus is the most common cause of severe, dehydrating diarrhea in infants and young children worldwide (typically aged 6 months to 2 years). It primarily causes a **malabsorptive and osmotic diarrhea** by infecting the mature enterocytes of the villi in the small intestine, leading to villous atrophy. The presence of fever and a normal WBC count is consistent with a viral etiology rather than an invasive bacterial one. The increased hematocrit is a marker of hemoconcentration due to dehydration. **2. Why other options are incorrect:** * **Cytomegalovirus (CMV):** Usually causes diarrhea in immunocompromised individuals (e.g., HIV/AIDS) or as part of congenital infections. It is not a common cause of acute diarrhea in an otherwise healthy 1-year-old. * **Salmonella typhi:** Causes Enteric Fever. While it can cause diarrhea in children, it typically presents with high-grade prolonged fever, hepatosplenomegaly, and significant systemic toxicity. * **Shigella dysenteriae:** Causes **inflammatory/bloody diarrhea (dysentery)**. It is characterized by high fever, abdominal cramps, tenesmus, and a high WBC count (often with a left shift), which contradicts the normal WBC count in this case. **Clinical Pearls for NEET-PG:** * **Mechanism:** Rotavirus NSP4 enterotoxin induces secretory diarrhea (the first known viral enterotoxin). * **Seasonality:** Peak incidence occurs in winter months ("Winter diarrhea"). * **Diagnosis:** Enzyme Immunoassay (EIA) or Latex agglutination for Rotavirus antigen in stool. * **Prevention:** Live attenuated oral vaccines (Rotarix, RotaTeq, Rotavac) are part of the National Immunization Schedule in India.

Question 160: A previously healthy 18-month-old girl is brought to the office with 2 days of irritability, poor appetite, and pulling at her left ear. She has no known allergies, and her temperature is 102.8 F. She is easily consoled by the mother and moves her neck spontaneously without discomfort. There is a clear discharge from the nares. The left tympanic membrane is erythematous, dull, and bulging. Which of the following virulence factors is generally absent in the strains of the causative organism that produce otitis media, compared with those that produce epiglottitis or meningitis?

A. Beta-Lactamase
B. IgA protease
C. Lipopolysaccharide
D. Polyribitol phosphate (Correct Answer)

Explanation: **Explanation:** The clinical presentation of fever, irritability, ear-tugging, and a bulging, erythematous tympanic membrane is diagnostic of **Acute Otitis Media (AOM)**. The most common bacterial causes are *Streptococcus pneumoniae*, **non-typeable *Haemophilus influenzae* (NTHi)**, and *Moraxella catarrhalis*. **1. Why Polyribitol Phosphate (PRP) is correct:** *Haemophilus influenzae* is classified into **encapsulated (typeable)** and **unencapsulated (non-typeable)** strains. The capsule of *H. influenzae* type b (Hib) is composed of **Polyribitol Phosphate (PRP)**, which is its primary virulence factor, allowing it to evade phagocytosis and cause invasive diseases like **epiglottitis, meningitis, and septic arthritis**. In contrast, **AOM**, sinusitis, and bronchitis are typically caused by **non-typeable *H. influenzae***, which lacks this polysaccharide capsule (and thus lacks PRP). **2. Why other options are incorrect:** * **A. Beta-Lactamase:** Both NTHi and Hib strains can produce beta-lactamase, conferring resistance to ampicillin. This is not a distinguishing factor between the two. * **B. IgA protease:** This enzyme cleaves secretory IgA to facilitate mucosal attachment. It is produced by both encapsulated and non-typeable strains of *H. influenzae*. * **C. Lipopolysaccharide (LPS):** This is a component of the outer membrane of all Gram-negative bacteria, including all strains of *H. influenzae*. It acts as an endotoxin causing inflammation. **Clinical Pearls for NEET-PG:** * **Hib Vaccine:** Targets the PRP capsule. Since the introduction of the vaccine, the incidence of epiglottitis and meningitis has plummeted, making **NTHi** the more common cause of *H. influenzae* mucosal infections (AOM). * **AOM Triad:** Bulging TM, decreased mobility (on pneumatic otoscopy), and erythema. * **Treatment:** Amoxicillin is first-line; Amoxicillin-Clavulanate is used if there is treatment failure (targeting beta-lactamase producing NTHi).

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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