Infectious Diseases Practice Questions

Q: A 5-year-old child presents with a honey-colored crusted lesion on their face. What is the most likely causative organism?

Streptococcus pyogenes. ***Streptococcus pyogenes*** - *Streptococcus pyogenes* (Group A Streptococcus) is the **most common causative organism** of **non-bullous impetigo**, which characteristically presents with **honey-colored crusted lesions**. - Non-bullous impetigo accounts for **70% of all impetigo cases** and typically affects the face, particularly around the mouth and nose. - The honey-colored crusts form when the serous exudate from ruptured vesicles dries on the skin surface. - **Important complication:** Post-streptococcal glomerulonephritis can occur 1-3 weeks after skin infection. *Staphylococcus aureus* - *S. aureus* is the primary cause of **bullous impetigo** (30% of cases), which presents with **fluid-filled bullae** rather than honey-colored crusts. - While *S. aureus* can co-infect with *S. pyogenes* in non-bullous impetigo, it is **not the primary pathogen** in the classic honey-crusted presentation described. - *S. aureus* produces exfoliative toxins that cause bullae formation in bullous impetigo. *Pseudomonas aeruginosa* - *Pseudomonas aeruginosa* is typically associated with **hot tub folliculitis**, infections in immunocompromised individuals, or puncture wounds. - Infections characteristically produce **bluish-green pus** with a fruity odor, not honey-colored crusts. - Not a typical cause of impetigo in healthy children. *Candida albicans* - *Candida albicans* causes **fungal infections** such as oral thrush, diaper dermatitis, or intertrigo in skin folds. - Presents with **erythematous patches with satellite lesions**, not honey-colored crusts. - The lesions are typically moist, macerated, and pruritic rather than crusted.

Q: What virus is primarily responsible for causing Exanthema subitum?

HHV-6. ***HHV-6*** - **Human Herpesvirus 6 (HHV-6)** is the primary causative agent of **Exanthema subitum**, also known as **Roseola infantum**. - This virus typically infects infants and young children, leading to a high fever followed by a characteristic rash. *HHV-8* - **Human Herpesvirus 8 (HHV-8)** is primarily associated with **Kaposi's sarcoma**, a cancer that affects individuals with weakened immune systems. - It is not implicated in Exanthema subitum. *Parvovirus* - **Parvovirus B19** causes **Fifth disease** (Erythema infectiosum), characterized by a "slapped cheek" rash. - Its clinical presentation, including the rash distribution and timing relative to fever, differs from Exanthema subitum. *Coxsackievirus* - **Coxsackievirus** is responsible for **Hand-foot-and-mouth disease** and herpangina, which involve rashes and lesions primarily on the hands, feet, and mouth or throat. - Exanthema subitum does not typically present with these specific dermatological features.

Q: An infant presents with hepatosplenomegaly and thrombocytopenia. Neuroimaging with CT shows periventricular calcifications. What is the most likely diagnosis?

Congenital cytomegalovirus infection. ***Congenital cytomegalovirus infection*** - **Periventricular calcifications** on neuroimaging are a classic and highly suggestive finding for congenital CMV infection. - **Hepatosplenomegaly** and **thrombocytopenia** are common systemic manifestations of congenital CMV, which can be severe. *Congenital rubella syndrome* - Rubella typically causes **sensorineural hearing loss**, ocular abnormalities (e.g., cataracts), and congenital heart defects (e.g., patent ductus arteriosus), rather than periventricular calcifications. - While hepatosplenomegaly and thrombocytopenia can occur, the specific brain calcification pattern points away from rubella. *Congenital herpes simplex virus infection* - HSV infection in neonates presents with a variety of symptoms, including skin vesicles, keratoconjunctivitis, and seizures. - Brain imaging often shows **focal necrosis** or **encephalitis**, not typically periventricular calcifications unless it's a very widespread and destructive process. *Congenital toxoplasmosis* - Congenital toxoplasmosis classic triad includes **chorioretinitis**, **hydrocephalus**, and **intracranial calcifications**, but these calcifications are typically scattered or diffuse rather than strictly periventricular. - While hepatosplenomegaly and thrombocytopenia can be present, the specific location of calcifications is a key differentiating factor.

Q: A 3-month-old baby presents with deafness, cataract, and patent ductus arteriosus. Which of the following is the most likely diagnosis?

Congenital rubella syndrome. ***Congenital rubella syndrome*** - The classic triad of **deafness**, **cataracts**, and **patent ductus arteriosus (PDA)** is highly characteristic of congenital rubella syndrome. - This syndrome results from **maternal rubella infection** during the first trimester of pregnancy. *Congenital herpes simplex virus infection* - Typically presents with **skin vesicles**, **keratoconjunctivitis**, and **encephalitis**. - **Deafness, cataracts, and PDA** are not common features of congenital HSV. *Congenital toxoplasmosis* - The classic triad involves **chorioretinitis**, **hydrocephalus**, and **intracranial calcifications**. - While it can cause microcephaly and seizures, **deafness, cataracts, and PDA** are not hallmark features. *Congenital cytomegalovirus infection* - Often causes **sensorineural hearing loss** and sometimes **chorioretinitis**, but the combination with **cataracts** and **PDA** is atypical. - Other common features include **periventricular calcifications**, **hepatosplenomegaly**, and **thrombocytopenia**.

Q: A child presents with a fever and a rash. Urine examination showed cells with owl's eye appearance. What is the most likely diagnosis?

Cytomegalovirus (CMV) infection. ***Cytomegalovirus (CMV) infection*** - The presence of cells with an **owl's eye appearance** in urine sediment is a classic histological hallmark of **CMV infection**. - CMV can cause a variety of symptoms in children, including **fever and rash**, making this the most likely diagnosis. *Herpes simplex virus infection* - HSV causes characteristic **vesicular lesions** on mucocutaneous surfaces, often associated with fever. - While HSV can cause systemic illness, it does not typically present with **owl's eye inclusions** in urine cells. *Toxoplasmosis caused by Toxoplasma gondii* - **Toxoplasmosis** can cause fever and rash, especially in congenital infections or immunocompromised individuals. - However, it does not lead to **owl's eye inclusions** in urinary cells, which are pathognomonic for CMV. *Infectious mononucleosis caused by Epstein-Barr virus* - **Infectious mononucleosis** commonly presents with fever, fatigue, and lymphadenopathy, sometimes with a rash. - **Epstein-Barr virus (EBV)** infection does not produce cells with an **owl's eye appearance** in the urine; that is specific to CMV.

Q: What is the most serious complication of measles?

Pneumonia. ***Pneumonia*** - **Pneumonia**, particularly **giant cell pneumonia**, is the most common cause of **measles-related deaths** in young children. - It results from the **direct viral infection** of the lungs or a **secondary bacterial superinfection**. *Croup* - **Croup (laryngotracheobronchitis)** can be a complication of measles, but it is typically **less severe** and **less life-threatening** than pneumonia. - It primarily affects the **upper airways**, causing a barking cough and stridor. *Meningo-encephalitis* - **Meningo-encephalitis** is a serious, albeit **less common**, complication of measles, occurring in approximately 1 in 1,000 cases. - While potentially fatal or leading to neurological sequelae, it is **outranked by pneumonia** in terms of overall mortality attributed to measles. *Otitis media* - **Otitis media** (middle ear infection) is a common complication of measles, but it is generally **not life-threatening**. - It usually responds well to **antibiotic treatment** and rarely leads to severe outcomes.

Q: All are true about congenital Toxoplasmosis EXCEPT which of the following?

Conjunctivitis. ***Conjunctivitis*** - **Conjunctivitis** is inflammation of the conjunctiva and is not a hallmark symptom of congenital toxoplasmosis. - While it can occur in an infant due to other causes, it is not specifically caused by *Toxoplasma gondii* infection. *Chorioretinitis* - **Chorioretinitis** is a classic ocular manifestation of congenital toxoplasmosis, leading to inflammation and scarring of the retina and choroid. - It can cause significant visual impairment and is a key component of the **classic triad** of symptoms. *Hydrocephalus* - **Hydrocephalus**, an abnormal accumulation of cerebrospinal fluid, is a severe neurological complication of congenital toxoplasmosis. - It results from obstruction of CSF flow due to inflammation or damage caused by the parasite in the brain. *Cerebral calcification* - **Cerebral calcifications** are highly suggestive of congenital toxoplasmosis, representing areas of brain tissue damage and healing where the parasite has been active. - These are typically visible on brain imaging and are a key diagnostic indicator.

Q: A child with a family history of allergies presents with pruritus on the face and convexities, followed by the development of numerous umbilicated vesicles that become pustular, hemorrhagic, and crusted. After two days, the child develops a high fever and lymphadenopathy. What is the most likely diagnosis?

Herpes simplex virus infection. ***Herpes simplex virus infection (Eczema herpeticum)*** - The presentation of **numerous umbilicated vesicles** that become **pustular, hemorrhagic, and crusted** in a child with atopic dermatitis is pathognomonic of **eczema herpeticum** (Kaposi varicelliform eruption). - **High fever** and **lymphadenopathy** developing after two days indicate systemic HSV infection, a characteristic feature of eczema herpeticum. - This is a **dermatological emergency** requiring immediate antiviral therapy (acyclovir) as it can progress to disseminated HSV infection with high morbidity. - The distribution on **face and convexities** matches typical atopic dermatitis sites where HSV superinfection occurs. *Eczema vaccinatum* - While clinically similar to eczema herpeticum, eczema vaccinatum is caused by **vaccinia virus** (smallpox vaccine complication). - This condition is **historically important but extremely rare today** since routine smallpox vaccination was discontinued in the 1970s-1980s. - In modern clinical practice and contemporary medical exams, eczema herpeticum (HSV) is the relevant diagnosis for this presentation. *Secondary infected atopic dermatitis* - Bacterial superinfections (usually *Staphylococcus aureus* or *Streptococcus*) typically produce **honey-colored crusts** (impetigo) or weeping, purulent lesions. - They do **not** produce the characteristic **umbilicated vesicles** described in this case. - The rapid, widespread vesicular eruption with systemic symptoms points to viral rather than bacterial etiology. *Molluscum contagiosum* - Presents as **discrete, pearly, dome-shaped umbilicated papules** that are chronic and typically asymptomatic. - Does **not** cause acute systemic symptoms like high fever and lymphadenopathy. - Does **not** progress to pustular, hemorrhagic, and crusted lesions as described in this case.

Q: At what age group is Streptococcus pneumoniae pneumonia most commonly observed?

< 5 years. ***< 5 years*** - *Streptococcus pneumoniae* pneumonia is particularly common and severe in **young children**, especially those under the age of 5, due to their developing immune systems. - This age group has a higher incidence of **invasive pneumococcal disease**, including pneumonia and meningitis, making vaccination crucial. *5 - 15 years* - While pneumonia can occur in this age group, it is **less common** than in very young children or older adults. - The immune system is generally more developed and effective at this age, leading to a **lower incidence** of severe pneumococcal infections. *20 - 25 years* - This age group generally has a robust immune system, making *Streptococcus pneumoniae* pneumonia **uncommon** unless there are underlying risk factors such as immunocompromise or chronic medical conditions. - Most cases of pneumonia in young adults are often due to **viral pathogens** or *Mycoplasma pneumoniae*. *30 - 40 years* - Similar to the 20-25 years age group, incidence of *Streptococcus pneumoniae* pneumonia remains **relatively low** in healthy individuals in their 30s and 40s. - Increased risk is typically associated with **chronic illnesses**, smoking, or conditions that weaken the immune system.

Question 1

A 5-year-old child presents with a honey-colored crusted lesion on their face. What is the most likely causative organism?

Accepted Answer

Streptococcus pyogenes

Answer

Staphylococcus aureus

Answer

Candida albicans

Answer

Pseudomonas aeruginosa

Question 2

What virus is primarily responsible for causing Exanthema subitum?

Accepted Answer

HHV-6

Answer

HHV-8

Answer

Parvovirus

Answer

Coxsackievirus

Question 3

An infant presents with hepatosplenomegaly and thrombocytopenia. Neuroimaging with CT    shows periventricular calcifications. What is the most likely diagnosis?

Accepted Answer

Congenital cytomegalovirus infection

Answer

Congenital rubella syndrome

Answer

Congenital herpes simplex virus infection

Answer

Congenital toxoplasmosis

Question 4

A 3-month-old baby presents with deafness, cataract, and patent ductus arteriosus. Which of the following is the most likely diagnosis?

Accepted Answer

Congenital rubella syndrome

Answer

Congenital herpes simplex virus infection

Answer

Congenital toxoplasmosis

Answer

Congenital cytomegalovirus infection

Question 5

A child presents with a fever and a rash. Urine examination showed cells with owl's eye appearance. What is the most likely diagnosis?

Accepted Answer

Cytomegalovirus (CMV) infection

Answer

Herpes simplex virus infection

Answer

Toxoplasmosis caused by Toxoplasma gondii

Answer

Infectious mononucleosis caused by Epstein-Barr virus

Question 6

What is the most serious complication of measles?

Accepted Answer

Pneumonia

Answer

Croup

Answer

Otitis media

Answer

Meningo-encephalitis

Question 7

An 11-year-old child with a history of streptococcal pharyngitis presents you with fever and arthralgia. There is no past history of rheumatic heart disease or features of carditis or valvular disease. How often is 600,000 IU of benzathine penicillin recommended for prophylaxis of rheumatic heart disease?

Accepted Answer

Once in three weeks for 5 years or till the age of 18, whichever is longer

Answer

Immediately

Answer

Thrice weekly lifelong

Answer

Once in three weeks for 10 years or till the age of 25, whichever is longer

Question 8

All are true about congenital Toxoplasmosis EXCEPT which of the following?

Accepted Answer

Conjunctivitis

Answer

Hydrocephalus

Answer

Cerebral calcification

Answer

Chorioretinitis

Question 9

A child with a family history of allergies presents with pruritus on the face and convexities, followed by the development of numerous umbilicated vesicles that become pustular, hemorrhagic, and crusted. After two days, the child develops a high fever and lymphadenopathy. What is the most likely diagnosis?

Accepted Answer

Herpes simplex virus infection

Answer

Secondary infected atopic dermatitis

Answer

Molluscum contagiosum

Answer

Eczema vaccinatum

Question 10

At what age group is Streptococcus pneumoniae pneumonia most commonly observed?

Accepted Answer

< 5 years

Answer

5 - 15 years

Answer

20 - 25 years

Answer

30 - 40 years

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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