Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 501: A child has received full rabies vaccination in December 2023 and now presented with an oozing wound on the great toe and the pet was also vaccinated. Next line of management is

A. RIG + 5 doses of vaccine
B. 5 doses of vaccines only
C. No vaccine required
D. 2 doses of Rabies vaccine (Correct Answer)

Explanation: ***2 doses of Rabies vaccine*** - For individuals who have received **previous full rabies vaccination** (either pre-exposure or post-exposure prophylaxis), a subsequent exposure requires only **two booster doses of vaccine on days 0 and 3**, regardless of wound category. - Even though this is a **Category III exposure** (oozing wound with break in skin), **no RIG is required** for previously immunized individuals as per WHO and APCRI guidelines. - The pre-existing immunity from the prior vaccination provides a **rapid anamnestic (memory) response**, eliminating the need for passive immunization or a full primary series. *RIG + 5 doses of vaccine* - This regimen is for individuals with **no prior vaccination history** and represents the full post-exposure prophylaxis for Category III exposures (transdermal bites, oozing wounds). - The child has been previously vaccinated, rendering this extensive protocol unnecessary and potentially harmful due to **immune complex formation** if RIG is given to an immune individual. *5 doses of vaccines only* - This approach is suitable for **previously unvaccinated individuals** with Category II exposure (nibbling, minor scratches without bleeding) where RIG may not be available. - However, in a previously vaccinated individual, the full 5-dose series is **excessive and not indicated** as immunity is already established. *No vaccine required* - Even with a previously vaccinated child and a vaccinated pet, there is still a **potential risk of exposure** to rabies, especially with a Category III wound (oozing wound). - Omitting vaccination entirely would be **negligent** and violates standard guidelines, as vaccine efficacy is not 100% and animal vaccination status can be uncertain or lapsed.

Question 502: An 8-year-old child presents with high-grade fever, restlessness and is found to have neck rigidity. On lab diagnosis, CSF glucose levels were decreased. What is the diagnosis?

A. A. Bacterial meningitis (Correct Answer)
B. B. Fungal meningitis
C. D. Viral meningitis
D. C. TB meningitis

Explanation: ***Bacterial meningitis*** - The key indicators for bacterial meningitis are **high-grade fever**, **neck rigidity**, **restlessness**, and most importantly, **decreased glucose levels in CSF**. - **Bacterial meningitis** is a severe infection of the meninges and CSF, it rapidly progresses, requiring prompt antibiotic treatment. *Fungal meningitis* - While fungal meningitis can present with similar symptoms, it typically has a **more subacute or chronic course** and is more common in **immunocompromised individuals**. - CSF findings in fungal meningitis often show **decreased glucose** but may also have **lymphocytic pleocytosis**, which is not specified here. *Viral meningitis* - **Viral meningitis** is characterized by normal or **slightly decreased glucose levels** in CSF, usually with **lymphocytic predominance**. - Although it presents with similar symptoms, it is almost always **self-limiting** and typically runs a mild course. *TB meningitis* - **TB meningitis** usually has a **more insidious onset** and a **subacute to chronic course**, not the acute presentation described. - While CSF glucose can be decreased, a key feature is typically **lymphocytic pleocytosis** and evidence of **tuberculosis infection** elsewhere.

Question 503: A 5-year-old presents with high fever, strawberry tongue, bilateral cervical lymphadenopathy, and a fine sandpaper-like rash that blanches on pressure. What is the diagnosis?

A. Measles
B. Scarlet fever (Correct Answer)
C. Kawasaki disease
D. Strep throat

Explanation: ***Scarlet fever*** - The combination of **high fever**, **strawberry tongue**, **bilateral cervical lymphadenopathy**, and a **fine sandpaper-like rash that blanches on pressure** is pathognomonic for scarlet fever. - Scarlet fever is caused by **Group A Streptococcus** (Streptococcus pyogenes) producing erythrogenic toxin. - The rash typically spares the perioral area (circumoral pallor) and desquamates after 1-2 weeks. *Measles* - While measles causes high fever, it presents with a **maculopapular rash** (not sandpaper-like), **Koplik spots** on buccal mucosa, and the **three Cs: cough, coryza, and conjunctivitis**. - The strawberry tongue and blanching sandpaper rash are not features of measles. *Kawasaki disease* - Kawasaki disease presents with **prolonged fever (≥5 days)**, **bilateral non-exudative conjunctivitis**, **strawberry tongue**, **polymorphous rash**, **extremity changes** (erythema/edema of hands/feet, later desquamation), and **unilateral cervical lymphadenopathy >1.5 cm**. - The **sandpaper-like blanching rash** is characteristic of scarlet fever, not Kawasaki disease, which has a polymorphous (variable) rash. - Kawasaki disease lacks the pharyngeal exudate and specific rash pattern seen in scarlet fever. *Strep throat* - **Strep throat** (streptococcal pharyngitis) is the underlying pharyngeal infection that can progress to scarlet fever when the streptococcal strain produces erythrogenic toxin. - Strep throat alone presents with **sore throat**, **fever**, **pharyngeal exudate**, and **tender cervical lymphadenopathy**, but does **not** produce the characteristic **strawberry tongue** and **sandpaper rash** that define scarlet fever. - The question describes scarlet fever specifically, not just uncomplicated strep throat.

Question 504: Mother had painful vesicular lesions over genitalia one year back. Now Baby is born with features of meningitis and fever and rashes in abdomen and forearm and died within a week. Scrapings from lesions showed multinucleated giant cells. What is the most likely organism?

A. B. Enterovirus 70
B. C. CMV
C. A. HSV2 (Correct Answer)
D. D. VZV

Explanation: ***HSV2*** - The mother's history of **genital vesicular lesions** and the infant's presentation with **meningitis**, **fever**, **rashes**, and rapid death are highly characteristic of **neonatal herpes simplex virus (HSV) infection**, typically caused by **HSV-2**. - **Multinucleated giant cells** on lesion scrapings (Tzanck smear) are a classic finding in HSV infections, indicating a herpesvirus etiology. - Neonatal HSV is typically acquired during **vaginal delivery** through an infected birth canal and presents with disseminated disease in the first week of life. *Enterovirus 70* - **Enterovirus 70** is primarily associated with **acute hemorrhagic conjunctivitis** and occasionally neurological complications, not neonatal meningitis with disseminated vesicular rash. - It does not cause **vesicular lesions** or lead to multinucleated giant cells on microscopic examination. *CMV* - **Cytomegalovirus (CMV)** can cause congenital infection with CNS involvement and rash, but typically presents with **intrauterine growth restriction**, **hepatosplenomegaly**, **hearing loss**, and **intracranial calcifications**. - The maternal history of **recurrent genital vesicular lesions** and **acute neonatal presentation** with multinucleated giant cells on Tzanck smear are not characteristic of CMV. - CMV causes **owl's eye inclusions** on histopathology, not multinucleated giant cells. *VZV* - **Varicella-zoster virus (VZV)** causes **chickenpox** and **shingles**, and while it can cause congenital or neonatal varicella with multinucleated giant cells, the maternal history of **recurrent genital vesicular lesions** points specifically to HSV-2. - Neonatal VZV typically occurs when the mother has **primary varicella infection** near delivery, not a history of genital lesions one year prior.

Question 505: A 4-year-old child with barking cough is diagnosed with croup. Which virus is most likely responsible?

A. Parainfluenza virus (Correct Answer)
B. Rhinovirus
C. Adenovirus
D. Respiratory syncytial virus

Explanation: ***Parainfluenza virus*** - **Parainfluenza viruses (PIV)** are the most common cause of **croup**, characterized by a **barking cough**, hoarseness, and inspiratory stridor. - PIV types 1 and 2 are particularly associated with acute laryngotracheobronchitis (croup) in young children. *Rhinovirus* - **Rhinoviruses** are the primary cause of the **common cold** and typically result in upper respiratory tract symptoms like runny nose, sneezing, and sore throat. - They are generally not associated with the severe laryngeal inflammation that causes the characteristic barking cough of croup. *Adenovirus* - **Adenoviruses** can cause a variety of respiratory illnesses, including pharyngitis and pneumonia, and sometimes mimic croup. - However, they are a less frequent cause of croup compared to parainfluenza viruses. *Respiratory syncytial virus* - **Respiratory syncytial virus (RSV)** is the leading cause of **bronchiolitis** and pneumonia in infants and young children. - While RSV can cause upper respiratory symptoms, it typically leads to wheezing and crackles rather than the barking cough of croup.

Question 506: A 6-year-old boy presents with fever, sore throat, and a sandpaper-like rash. The rapid strep test is positive. What is the most appropriate treatment?

A. Amoxicillin (Correct Answer)
B. Ceftriaxone
C. Penicillin V
D. Erythromycin

Explanation: ***Amoxicillin*** - **Amoxicillin** is the **first-line treatment** for **Group A streptococcal pharyngitis** (strep throat) according to **AAP and IDSA guidelines**. - It is equally effective as penicillin V in eradicating *Streptococcus pyogenes* and preventing **rheumatic fever** and **post-streptococcal glomerulonephritis**. - Amoxicillin is preferred over penicillin V due to **better palatability**, **improved compliance** in children, and **convenient once-daily dosing option**. - The patient's presentation with fever, sore throat, and sandpaper rash (classic for **scarlet fever**) plus positive rapid strep test confirms the diagnosis. *Penicillin V* - **Penicillin V** is an acceptable alternative first-line treatment for strep throat with equal efficacy. - However, amoxicillin is generally preferred in pediatric practice due to better taste and compliance. - Both antibiotics have similarly low resistance rates for Group A Streptococcus. *Ceftriaxone* - **Ceftriaxone** is a third-generation cephalosporin reserved for severe infections, suspected complications, or patients unable to tolerate oral medications. - It is not indicated as first-line treatment for uncomplicated **streptococcal pharyngitis**. - May be used in cases of treatment failure or penicillin allergy. *Erythromycin* - **Erythromycin** is a macrolide antibiotic reserved for patients with **penicillin allergy**. - However, **azithromycin** or **clarithromycin** are now preferred over erythromycin due to better tolerability and dosing convenience. - Not indicated as first-line therapy when penicillin or amoxicillin can be used.

Question 507: For suspected pertussis in a child with a characteristic cough, which diagnostic test provides the highest sensitivity and specificity?

A. Nasopharyngeal swab (Correct Answer)
B. Tracheal aspiration
C. Cough plate culture
D. Sputum culture

Explanation: ***Nasopharyngeal swab for PCR testing*** - **PCR (polymerase chain reaction)** testing using nasopharyngeal swab specimens provides the **highest sensitivity (70-90%) and specificity (approaching 100%)** for pertussis diagnosis - The nasopharyngeal swab is collected using a **flocked swab placed deep into the nasopharynx**, ensuring contact with the posterior wall where *Bordetella pertussis* colonizes - PCR detects bacterial DNA and is superior to culture-based methods, especially in patients who have received antibiotics or are in later stages of illness - This is the **preferred diagnostic method** recommended by CDC and WHO *Tracheal aspiration* - This is an **invasive procedure** reserved only for patients requiring intubation and mechanical ventilation - While it can yield respiratory secretions, it carries significant risks and is **not indicated for routine pertussis diagnosis** - The risk-benefit ratio does not support its use when non-invasive methods are available *Cough plate culture* - This older method involves placing a culture plate in front of the patient's mouth during coughing episodes - It has **significantly lower sensitivity** compared to nasopharyngeal PCR and is difficult to standardize - **Culture methods** in general have lower sensitivity (12-60%) than PCR and require specialized media and prolonged incubation *Sputum culture* - Sputum is **not an appropriate specimen** for pertussis diagnosis as *Bordetella pertussis* primarily colonizes the **nasopharynx**, not the lower respiratory tract - Sputum samples contain oral flora that can interfere with detection and do not accurately reflect nasopharyngeal colonization

Question 508: Which organism is the most common cause of severe childhood diarrhea worldwide?

A. Rotavirus (Correct Answer)
B. Norovirus
C. Salmonella
D. Giardia lamblia

Explanation: ***Rotavirus*** - **Rotavirus** is the leading cause of **severe dehydrating diarrhea** in young children globally, particularly in low- and middle-income countries. - It primarily affects infants and young children under 5 years of age, leading to millions of hospitalizations worldwide annually. - Although **rotavirus vaccines** (RotaTeq, Rotarix) have significantly reduced disease burden in countries with high vaccine coverage, rotavirus remains the most common cause of severe childhood diarrhea globally due to incomplete vaccine implementation in many regions. *Norovirus* - **Norovirus** is a common cause of **gastroenteritis** in all age groups but is more associated with outbreaks in closed communities (e.g., cruise ships, schools) and less frequently causes severe, dehydrating illness in children compared to rotavirus. - While highly contagious, its impact on severe childhood morbidity and mortality is less significant than rotavirus. *Salmonella* - **Salmonella** can cause severe diarrhea, particularly **typhoid fever** or **enterocolitis**, but it's not the most common cause of severe childhood diarrhea worldwide. - Its prevalence varies geographically, and it is usually acquired through contaminated food or water. *Giardia lamblia* - **Giardia lamblia** is a **parasite** that causes **giardiasis**, which can lead to chronic diarrhea, malabsorption, and growth faltering in children. - While it's a significant cause of diarrheal disease, it typically causes subacute or chronic symptoms rather than acute severe, dehydrating episodes most commonly associated with childhood morbidity.

Question 509: A 7-year-old child presents with persistent fever, abdominal pain, and a 'rose spots' rash on the abdomen. What is the most likely diagnosis?

A. Typhoid fever (Correct Answer)
B. Scarlet fever
C. Measles
D. Rubella

Explanation: ***Typhoid fever*** - **Persistent fever**, **abdominal pain**, and characteristic **'rose spots' rash** on the abdomen are classic clinical features of typhoid fever, caused by *Salmonella typhi*. - This illness can progress to involve multiple organs and requires prompt antibiotic treatment. *Scarlet fever* - Characterized by a **fine, sandpaper-like rash** that blanches with pressure, predominantly on the trunk and extremities, often accompanied by a **strawberry tongue**. - It is caused by *Streptococcus pyogenes* and typically follows a streptococcal pharyngitis, which is not suggested by the symptoms provided. *Measles* - Presents with a **maculopapular rash** that begins on the face and spreads downwards, often preceded by a **prodrome of fever**, **cough**, **coryza**, and **conjunctivitis**, with characteristic **Koplik spots** in the mouth. - The rash is not described as "rose spots" nor is it limited to the abdomen initially. *Rubella* - Characterized by a milder **maculopapular rash** that starts on the face and spreads to the trunk and extremities, often accompanied by **postauricular** and **occipital lymphadenopathy**. - The rash is less distinct than measles and does not typically present as "rose spots" or with severe abdominal pain.

Question 510: A 7-year-old girl presents with a sore throat, fever, and a red, swollen throat with white patches. A rapid strep test is positive. What is the most likely diagnosis?

A. Viral pharyngitis
B. Streptococcal pharyngitis (Correct Answer)
C. Infectious mononucleosis
D. Diphtheria

Explanation: ***Streptococcal pharyngitis*** - The combination of **sore throat, fever, red and swollen throat with white patches**, and a **positive rapid strep test** is highly indicative of streptococcal pharyngitis (strep throat). - This bacterial infection, typically caused by *Streptococcus pyogenes* (Group A Strep), requires antibiotic treatment to prevent complications like **rheumatic fever**. *Viral pharyngitis* - While viral pharyngitis can cause a sore throat and fever, it generally does not present with **white exudates** to the extent described. - A **rapid strep test would be negative** in viral pharyngitis, differentiating it from this case. *Infectious mononucleosis* - Infectious mononucleosis, caused by the **Epstein-Barr virus**, can cause exudative tonsillitis, but it's often accompanied by **lymphadenopathy** (especially in the posterior cervical chain) and **splenomegaly**, which are not mentioned here. - Critically, a **rapid strep test would be negative**, ruling out strep as the primary cause. *Diphtheria* - Diphtheria is characterized by the formation of a **thick, gray pseudomembrane** that can obstruct the airway and is difficult to dislodge. - While it causes a sore throat and fever, it is rare in vaccinated populations and a **rapid strep test would be negative**.

Practice by Chapter

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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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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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