Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 551: A baby from a second degree consanguineous marriage presents with diarrhoea and redness in the perianal diaper area. What is the most likely diagnosis?

A. Fungal infection (Correct Answer)
B. Shigella infection
C. Salmonella infection
D. Lactose intolerance

Explanation: ***Fungal infection (Candida diaper dermatitis)*** - **Diarrhea with perianal diaper rash** is the classic presentation of **Candida (fungal) diaper dermatitis**, the most common cause of diaper rash in infants with diarrhea. - **Diarrhea increases skin moisture and alters pH**, creating optimal conditions for **Candida albicans overgrowth**. - **Perianal involvement with bright erythema** is characteristic of Candida, often with **satellite lesions** and involvement of skin folds. - This is a **clinical diagnosis** based on distribution pattern and association with diarrhea; consanguinity is not directly relevant to this common condition. *Lactose intolerance* - **Congenital lactase deficiency** is extremely rare (< 50 cases worldwide) and unlikely to be the primary diagnosis. - While **secondary lactose intolerance** can occur with gastroenteritis causing diarrhea, it doesn't explain the **specific perianal rash pattern** described. - The perianal redness in lactose malabsorption would be **irritant contact dermatitis** from acidic stools, which would secondarily get infected with **Candida** - making fungal infection the more complete diagnosis. *Shigella infection* - Typically presents with **bloody diarrhea (dysentery)**, high fever, abdominal cramps, and tenesmus. - Would not specifically cause the **perianal diaper rash pattern** characteristic of Candida. - Consanguinity doesn't predispose to this bacterial infection. *Salmonella infection* - Usually presents with **fever, vomiting, and systemic symptoms** along with diarrhea. - May cause bloody or non-bloody diarrhea but doesn't explain the **characteristic perianal redness pattern**. - Not associated with consanguinity as it's an acquired infectious disease.

Question 552: What is the most common symptom of AIDS in infants?

A. Persistent cough
B. Lymphadenopathy
C. GI infection
D. Failure to thrive (Correct Answer)

Explanation: ***Failure to thrive*** - **Growth retardation** and **weight loss** in infants with AIDS are directly related to the chronic stress of the infection, recurrent infections, and malabsorption. - This symptom reflects the body's inability to maintain normal growth and development due to the underlying severe **immunosuppression**. *GI infection* - While **gastrointestinal infections** are common in infants with AIDS due to immune compromise, they are a consequence rather than the initial, most common presenting symptom. - They often contribute to, but are not synonymous with, the broader syndrome of **failure to thrive**. *Persistent cough* - A **persistent cough** can be a symptom of various opportunistic infections, such as *Pneumocystis jirovecii* pneumonia (PJP), which is common in infants with AIDS. - However, it is not the single most common *initial* symptom across all presentations of pediatric AIDS. *Lymphadenopathy* - **Lymphadenopathy** (swollen lymph nodes) is a very common sign of HIV infection in children due to chronic immune stimulation. - While prevalent, it is often a *physical finding* on examination rather than the primary symptom that parents typically notice leading to presentation, which is often related to the child's overall well-being and growth.

Question 553: The most common cause of meningitis in children aged 5 yrs is-

A. Staphylococcus
B. E.coli
C. H. influenzae
D. S. pneumoniae (Correct Answer)

Explanation: ***S. pneumoniae*** - **_Streptococcus pneumoniae_** (Pneumococcus) is the **most common cause of bacterial meningitis** in children aged 5 years and older, as well as in adults. - Widespread vaccination has reduced its incidence but it remains a significant pathogen. *H. influenzae* - **_Haemophilus influenzae_ type b (Hib)** was a major cause of meningitis in young children, but its incidence has **drastically decreased** due to the routine **Hib vaccine**. - Without vaccination, it would still be a significant cause in this age group, but with high vaccine coverage, it is less common than _S. pneumoniae_. *Staphylococcus* - **_Staphylococcus aureus_** and other staphylococcal species are **less common causes of meningitis** in otherwise healthy children. - They are more typically associated with meningitis following **neurosurgery**, trauma, or in immunocompromised patients. *E.coli* - **_Escherichia coli_** is a common cause of **neonatal meningitis** (in infants less than 3 months old), often acquired during passage through the birth canal. - It is **rarely a cause of meningitis** in children aged 5 years.

Question 554: Which immunization is typically given at 6 months of age?

A. Measles vaccine
B. DPT vaccine (Correct Answer)
C. BCG vaccine
D. None of the options

Explanation: **DPT vaccine** - The DPT (diphtheria, pertussis, and tetanus) vaccine is administered in multiple doses during infancy as part of the primary immunization series. - At **6 months of age**, the **third dose of DPT** is typically given (following doses at 6 weeks, 10 weeks, and 14 weeks according to the Indian immunization schedule). - Among the options provided, DPT is the only vaccine routinely administered at 6 months of age. - This vaccine protects against three serious bacterial infections: **diphtheria**, which can cause breathing problems; **pertussis (whooping cough)**, a severe respiratory illness; and **tetanus**, which causes painful muscle spasms. *Measles vaccine* - The measles vaccine (given as part of the **MMR vaccine** or as MR vaccine in India) is typically administered at **9 to 12 months of age** for the first dose, and a second dose between 15-18 months or 4-6 years. - It is not routinely given at 6 months, as maternal antibodies can interfere with its effectiveness at this younger age. *BCG vaccine* - The BCG (Bacillus Calmette-Guérin) vaccine protects against **tuberculosis** and is given at **birth** or in early infancy as a single dose. - It is not administered at 6 months of age. *None of the options* - This option is incorrect because the **DPT vaccine** (third dose) is a standard immunization given at 6 months of age according to the Indian immunization schedule. - Multiple vaccines are actually given at 6 months (including OPV, Hepatitis B, Hib, PCV), but among the listed options, only DPT is correct.

Question 555: What is the most common cause of Hemolytic Uremic Syndrome (HUS) in children?

A. Salmonella typhi
B. Shigella dysenteriae
C. E. coli O157:H7 (Correct Answer)

Explanation: ***E. coli O157:H7*** - This **Shiga toxin-producing E. coli (STEC)** strain is the predominant cause of **diarrhea-associated HUS** in children. - The Shiga toxin damages endothelial cells, leading to **thrombotic microangiopathy**, red blood cell fragmentation, and acute kidney injury. - Accounts for approximately **90% of typical HUS cases** in children. *Salmonella typhi* - This bacterium is primarily responsible for causing **typhoid fever**, a systemic illness characterized by prolonged fever, abdominal pain, and sometimes rash. - While it can cause gastrointestinal symptoms, it is **not a cause of HUS**. *Shigella dysenteriae* - This bacterium causes **shigellosis**, an acute inflammatory colitis characterized by bloody diarrhea. - Although *Shigella dysenteriae* type 1 produces **Shiga toxin** and can cause HUS, it is a **less common cause in most developed countries** compared to *E. coli O157:H7*. - More commonly associated with HUS in developing countries with poor sanitation.

Question 556: Ideal temperature for DPT storage?

A. Room temperature
B. 4 to 8°C (Correct Answer)
C. 0 to - 20°C
D. None of the options

Explanation: ***4 to 8°C*** - The ideal temperature for DPT (diphtheria, pertussis, tetanus) vaccine storage is between **+2°C and +8°C** (or 35°F and 46°F), which is the standard refrigerator temperature range. - This temperature range is crucial for maintaining the **potency** and **efficacy** of the vaccine, preventing **degradation** due to excessive heat or cold. *Room temperature* - Storing DPT vaccines at **room temperature** (typically 20-25°C or 68-77°F) for extended periods can lead to a **loss of potency** as heat can degrade vaccine components. - While short-term excursions within this range might be permissible under specific conditions (e.g., during transport), it is not the ideal long-term storage solution. *0 to - 20°C* - DPT vaccines, particularly the **whole-cell pertussis (wP)** component, can be **damaged by freezing**. - Temperatures below 0°C can cause the **adjuvant** (usually aluminum salt) to separate, leading to a loss of efficacy and potential local reactions at the injection site. *None of the options* - This option is incorrect because **4 to 8°C** is indeed the established and recommended ideal storage temperature for DPT vaccines.

Question 557: Which of the following diseases is not effectively prevented by maternal antibodies transferred during pregnancy?

A. Whooping cough (Pertussis) (Correct Answer)
B. Mumps
C. Rubella
D. Measles

Explanation: ***Whooping cough (Pertussis)*** - **Maternal antibodies** against pertussis are **poorly transferred** across the placenta, offering **limited protection** to the neonate. - Infants remain highly vulnerable to pertussis, necessitating early vaccination or **cocooning strategies** (vaccinating close contacts). *Mumps* - Maternal antibodies provide **effective passive immunity** to the infant for several months, protecting against mumps. - This protection wanes, making **childhood vaccination (MMR)** crucial. *Rubella* - **Maternal antibodies** against rubella are **effectively transferred**, providing good protection to the infant during the first 6-12 months of life. - This is particularly important as congenital rubella syndrome can cause severe birth defects. *Measles* - Infants born to mothers with measles immunity receive **strong passive maternal antibody protection**, which typically lasts until 6-9 months of age. - This initial protection is why the first dose of the **MMR vaccine** is usually given around 12 months.

Question 558: Rubella is known to cause all of the following conditions except:

A. Conduction defects
B. VSD
C. Microcephaly
D. Glaucoma (Correct Answer)

Explanation: ***Glaucoma*** - While rubella can cause **ocular defects** such as **cataracts** and **pigmentary retinopathy**, glaucoma is not a typical congenital manifestation of rubella syndrome. - **Congenital glaucoma** is more commonly associated with other genetic syndromes or developmental anomalies. *Microcephaly* - **Microcephaly** is a recognized neurological complication of congenital rubella syndrome, resulting from impaired brain development due to viral infection. - The rubella virus can interfere with the **proliferation and migration** of neuronal cells during fetal development. *VSD* - **Ventricular septal defect (VSD)** is a common congenital heart defect associated with congenital rubella syndrome. - Other cardiac anomalies seen include **patent ductus arteriosus (PDA)** and **pulmonary artery stenosis**. *Conduction defects* - **Conduction defects** and other **cardiac arrhythmias** can occur in congenital rubella syndrome due to direct viral damage to the developing cardiac conduction system. - This can manifest as **bradyarrhythmias** or various degrees of **heart block**.

Question 559: A child presents with fever, abdominal cramps, and bloody stools. Which organism is the most likely cause?

A. ETEC
B. EAEC
C. EHEC (Correct Answer)
D. EPEC

Explanation: ***EHEC*** - **Enterohemorrhagic *E. coli*** (EHEC), particularly O157:H7, is well-known for causing **bloody diarrhea** and severe abdominal cramps, especially in children, due to the production of **Shiga toxins**. - Shiga toxins can lead to **hemolytic uremic syndrome (HUS)**, a serious complication characterized by acute kidney failure, hemolytic anemia, and thrombocytopenia. *ETEC* - **Enterotoxigenic *E. coli*** (ETEC) is a common cause of **traveler's diarrhea** and typically presents with **watery diarrhea**, abdominal cramps, and low-grade fever. - It primarily invades the small intestine and produces toxins that promote fluid and electrolyte secretion, but it does **not typically cause bloody stools**. *EPEC* - **Enteropathogenic *E. coli*** (EPEC) typically causes **watery diarrhea** in infants and young children by disrupting the intestinal microvilli, leading to malabsorption. - It does **not produce Shiga toxins** and is generally associated with non-bloody, watery stools and vomiting. *EAEC* - **Enteroaggregative *E. coli*** (EAEC) is associated with persistent diarrhea, especially in children and immunocompromised individuals, due to its ability to adhere to intestinal cells in an aggregative manner. - While it can cause **secretory, watery diarrhea**, it is rarely associated with bloody stools.

Question 560: Which among the following diagnostic criteria is most characteristic of Kawasaki disease?

A. Non-exudative bilateral conjunctival injection (Correct Answer)
B. Unilateral cervical lymphadenopathy
C. Gastrointestinal symptoms
D. Periungual desquamation (peeling of skin around the nails)

Explanation: ***Non-exudative bilateral conjunctival injection*** - **Non-exudative bilateral conjunctival injection** is a key diagnostic criterion for Kawasaki disease, indicating inflammation without pus or discharge. - This finding is one of the five principal clinical features used to diagnose the condition, alongside fever of at least five days. *Unilateral cervical lymphadenopathy* - **Unilateral cervical lymphadenopathy** is a common diagnostic criterion for Kawasaki disease, but it must be larger than **1.5 cm** to be considered significant. - While present in many cases, its unilateral nature and specific size requirement make it less universally characteristic than bilateral conjunctival injection. *Gastrointestinal symptoms* - **Gastrointestinal symptoms**, such as diarrhea, vomiting, and abdominal pain, can occur in Kawasaki disease but are **non-specific** and not primary diagnostic criteria. - These symptoms are often present due to systemic inflammation but do not directly help in distinguishing Kawasaki from other febrile illnesses. *Periungual desquamation (peeling of skin around the nails)* - **Periungual desquamation** is a characteristic feature of **subacute or convalescent phase** of Kawasaki disease, occurring typically *after* the acute febrile stage. - While highly suggestive of Kawasaki disease, it is not an acute diagnostic criterion used to initially identify the illness during its active phase.

Practice by Chapter

Vaccine-Preventable Diseases

Practice Questions

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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