Infectious Diseases Practice Questions

Q: What is the most common complication of measles?

Otitis media. **Explanation:** Measles (Rubeola) is a highly contagious viral infection characterized by high fever, cough, coryza, conjunctivitis (the 3 Cs), and the pathognomonic Koplik spots. While the virus itself causes significant morbidity, its complications are frequent. **Why Otitis Media is the correct answer:** **Otitis media** is statistically the **most common complication** of measles, occurring in approximately 7–10% of cases. It occurs due to the virus causing inflammation of the respiratory mucosa and secondary bacterial invasion, leading to middle ear infection. For NEET-PG, it is crucial to distinguish between the "most common" and "most fatal" complication. **Analysis of Incorrect Options:** * **Orchitis (A):** This is a classic complication of **Mumps**, not Measles. It typically occurs in post-pubertal males. * **Pneumonia (B):** This is the **most common cause of death** (most fatal complication) associated with measles in children. It can be primary viral (Hecht’s giant cell pneumonia) or secondary bacterial. * **Seizures (D):** While febrile seizures can occur due to high fever in measles, they are not as frequent as otitis media. **High-Yield Clinical Pearls for NEET-PG:** * **Most common complication:** Otitis media. * **Most common cause of death:** Pneumonia. * **Most serious/delayed complication:** Subacute Sclerosing Panencephalitis (SSPE), occurring years after the initial infection. * **Vitamin A supplementation:** Essential in management as it reduces the severity of complications and mortality. * **Infectivity:** Maximum during the **pre-eruptive (prodromal) stage**. The patient is infectious from 4 days before to 4 days after the appearance of the rash.

Q: A 6-month-old child presents with recurrent seizures and poor development. The evaluation reveals hydrocephalus, impaired movement of the extremities, hypotonia, and retinal abnormalities. A computerized tomography (CT) scan demonstrates large ventricles and calcified lesions. Which of the following is the most likely diagnosis?

Toxoplasmosis. ### Explanation The clinical presentation of hydrocephalus, intracranial calcifications, and retinal abnormalities (chorioretinitis) forms the classic **Sabin Triad**, which is pathognomonic for **Congenital Toxoplasmosis**. **1. Why Toxoplasmosis is Correct:** Congenital Toxoplasmosis is caused by the transplacental transmission of *Toxoplasma gondii*. The CT findings of **diffuse intracranial calcifications** (scattered throughout the parenchyma) and ventriculomegaly (obstructive hydrocephalus due to aqueductal stenosis) are hallmark features. The "poor development" and "impaired movement" reflect the neurological sequelae of the infection, while "retinal abnormalities" typically refer to chorioretinitis, the most common ocular manifestation. **2. Why the Other Options are Incorrect:** * **Tay-Sachs Disease:** While it presents with developmental regression and hypotonia, it is characterized by a **cherry-red spot** on the macula and **macrocephaly** (due to GM2 ganglioside accumulation), not hydrocephalus or calcifications. * **Congenital Hydrocephalus:** This is a structural finding, not a primary diagnosis. It does not explain the intracranial calcifications or retinal abnormalities. * **Kernicterus:** This results from severe unconjugated hyperbilirubinemia. While it causes hypotonia (early) and movement disorders (choreoathetosis), it does not present with intracranial calcifications or hydrocephalus. **3. NEET-PG High-Yield Pearls:** * **Calcification Pattern:** In Toxoplasmosis, calcifications are **diffuse/scattered**; in Congenital CMV, they are typically **periventricular**. * **Classic Triad (Sabin Triad):** Hydrocephalus, Intracranial calcifications, and Chorioretinitis. * **Treatment:** The standard regimen is **Pyrimethamine, Sulfadiazine, and Folinic acid** for one year. * **Source:** Usually acquired via oocysts in cat feces or undercooked meat.

Q: Primary pneumococcal peritonitis in children is most commonly associated with which of the following conditions?

Cirrhosis. **Explanation:** **Primary Peritonitis** (also known as Spontaneous Bacterial Peritonitis or SBP) is an infection of the peritoneal fluid without an evident intra-abdominal source of perforation. **Why Cirrhosis is the Correct Answer:** In children, the most common underlying condition predisposing to primary peritonitis is **Nephrotic Syndrome**, followed closely by **Cirrhosis** (chronic liver disease). In patients with cirrhosis, the development of ascites provides a medium for bacterial growth. The underlying pathophysiology involves **impaired host defenses**, specifically decreased opsonic activity in the ascitic fluid and portosystemic shunting, which allows bacteria to bypass the hepatic reticuloendothelial system (Kupffer cells). While *Streptococcus pneumoniae* is the classic organism associated with primary peritonitis in Nephrotic Syndrome, it is also a major pathogen in cirrhotic patients, alongside Gram-negative organisms like *E. coli*. **Analysis of Incorrect Options:** * **B. Lymphoma:** While lymphoma causes immunosuppression, it is more commonly associated with opportunistic infections or secondary peritonitis due to bowel obstruction/perforation rather than primary pneumococcal peritonitis. * **C. Carcinoid tumors:** These are neuroendocrine tumors that do not typically predispose patients to spontaneous bacterial infections of the peritoneum. **NEET-PG High-Yield Pearls:** * **Most common organism overall:** *Streptococcus pneumoniae* is the most common cause of primary peritonitis in children (especially those with Nephrotic Syndrome). * **Clinical Presentation:** Sudden onset of fever, abdominal pain, and rebound tenderness in a child with pre-existing ascites. * **Diagnosis:** Established by paracentesis showing an **Absolute Neutrophil Count (ANC) >250 cells/mm³**. * **Treatment of choice:** Third-generation cephalosporins (e.g., Cefotaxime or Ceftriaxone).

Q: Which of the following statements about HIV in neonates is incorrect?

The transmission rate during pregnancy exceeds 90%.. **Explanation:** **1. Why Option C is the correct (incorrect statement):** The transmission rate of HIV from an untreated mother to her child is approximately **15% to 45%**, not >90%. With modern Prevention of Mother-to-Child Transmission (PMTCT) interventions—including Highly Active Antiretroviral Therapy (HAART), elective cesarean section, and avoidance of breastfeeding—this risk can be reduced to **less than 1–2%**. Therefore, the statement claiming a >90% transmission rate is factually incorrect. **2. Analysis of other options:** * **Option A:** Diagnosis in neonates is complex because maternal IgG antibodies cross the placenta and persist for up to 18 months. Therefore, standard ELISA/Western Blot cannot distinguish between infant infection and maternal antibodies. Diagnosis requires **HIV DNA or RNA PCR** (Nucleic Acid Testing). * **Option B:** Failure to thrive (FTT), persistent diarrhea, and recurrent infections (like oral candidiasis) are classic early clinical presentations of pediatric HIV. * **Option C:** Vertical transmission is the primary route of pediatric HIV, occurring in utero (transplacental), during delivery (birth canal), or postpartum (breastfeeding). **Clinical Pearls for NEET-PG:** * **Gold Standard Diagnosis:** HIV DNA PCR is the preferred test for infants <18 months. The first test is usually done within 4–6 weeks of birth. * **Prophylaxis:** All HIV-exposed infants should receive **Nevirapine** (or Zidovudine) prophylaxis immediately after birth for 6–12 weeks. * **Pneumocystis jirovecii (PJP) Prophylaxis:** Started at 6 weeks of age for all HIV-exposed infants until infection is ruled out. * **Breastfeeding:** In India (per NACO guidelines), exclusive breastfeeding is recommended for the first 6 months if replacement feeding is not "AFASS" (Affordable, Feasible, Acceptable, Sustainable, and Safe).

Q: A dome-shaped skull with a high forehead in an infant with slight hydrocephalus (Olympian brow) is characteristic of which condition?

Congenital syphilis. **Explanation:** The correct answer is **Congenital Syphilis**. The "Olympian brow" refers to a prominent, dome-shaped forehead caused by bony overgrowth (frontal bossing) due to chronic periostitis of the frontal and parietal bones. This is a classic late manifestation of congenital syphilis, often associated with other stigmata such as a saddle nose, Hutchinson’s teeth, and Mulberry molars. **Analysis of Options:** * **Marasmus:** While infants with severe malnutrition (Marasmus) may appear to have a large head relative to their wasted body ("monkey facies"), they do not exhibit true frontal bossing or the specific "Olympian brow" bony deformity. * **Rickets:** Rickets is a common cause of **frontal bossing** (caput quadratum), but the skull typically appears "boxy" or square-shaped rather than the specific "Olympian" dome-shape. Rickets is also characterized by craniotabes and a delayed closure of the anterior fontanelle. * **Arnold-Chiari Syndrome:** This involves structural defects in the cerebellum and brainstem. While it is frequently associated with hydrocephalus, it does not produce the specific "Olympian brow" bony configuration. **High-Yield Clinical Pearls for NEET-PG:** * **Hutchinson’s Triad:** Interstitial keratitis, Eighth nerve deafness, and Hutchinson’s teeth (notched incisors). * **Early Congenital Syphilis ( 2 years):** Clutton’s joints (painless knee effusion), Saber shins, and Higoumenakis sign (thickening of the medial end of the clavicle).

Q: A 7-month-old child presents with microcephaly. What is the most likely etiology for this clinical presentation?

Cytomegalovirus (CMV). **Explanation:** **Microcephaly** is a hallmark clinical feature of certain congenital infections, most notably **Cytomegalovirus (CMV)**. 1. **Why CMV is the correct answer:** CMV is the most common congenital infection worldwide. It characteristically causes central nervous system (CNS) insults during fetal development, leading to impaired brain growth and subsequent **microcephaly**. A high-yield diagnostic feature of CMV is **periventricular calcifications**, which helps differentiate it from other TORCH infections. 2. **Analysis of Incorrect Options:** * **Toxoplasma:** While congenital Toxoplasmosis affects the CNS, it more commonly presents with **macrocephaly** (due to obstructive hydrocephalus) and **diffuse intracerebral calcifications** (scattered throughout the parenchyma, not just periventricular). * **Rubella:** Congenital Rubella Syndrome (CRS) can cause microcephaly, but its "classic triad" consists of **cataracts, sensorineural hearing loss, and congenital heart disease** (PDA). CMV is statistically a more frequent cause of isolated microcephaly in clinical vignettes unless the triad is mentioned. * **Mumps:** Mumps is not a classic member of the TORCH group and is not typically associated with congenital malformations or microcephaly. **High-Yield Clinical Pearls for NEET-PG:** * **CMV:** Most common cause of non-syndromic sensorineural hearing loss (SNHL). Look for **periventricular calcifications**. * **Toxoplasmosis:** Look for the triad of **Chorioretinitis, Hydrocephalus, and Intracranial calcifications**. * **Zika Virus:** Currently the most "potent" viral cause of extreme microcephaly and fetal brain disruption sequence. * **Microcephaly Definition:** Head circumference < 3 Standard Deviations (SD) below the mean for age and sex.

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

Given to a newborn contact. **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 1

What is the most common complication of measles?

Accepted Answer

Otitis media

Answer

Orchitis

Answer

Pneumonia

Answer

Seizures

Question 2

A 6-month-old child presents with recurrent seizures and poor development. The evaluation reveals hydrocephalus, impaired movement of the extremities, hypotonia, and retinal abnormalities. A computerized tomography (CT) scan demonstrates large ventricles and calcified lesions. Which of the following is the most likely diagnosis?

Accepted Answer

Toxoplasmosis

Answer

Tay-Sachs disease

Answer

Congenital hydrocephalus

Answer

Kernicterus

Question 3

Primary pneumococcal peritonitis in children is most commonly associated with which of the following conditions?

Accepted Answer

Cirrhosis

Answer

Lymphoma

Answer

Carcinoid tumors

Answer

None of the above

Question 4

A 2-month-old infant presents for her first immunization. Physical examination reveals shivering and a body temperature of 39°C. The mother reports the infant is constantly crying, irritable, and refusing to feed. What is the most appropriate medical intervention in this case?

Accepted Answer

Delay immunization; return in 2-3 days

Answer

Administer immunization as per schedule

Answer

Administer immunizations one week apart

Answer

Postpone immunization for 6 months

Question 5

Which of the following statements about HIV in neonates is incorrect?

Accepted Answer

The transmission rate during pregnancy exceeds 90%.

Answer

Diagnosis cannot be accurately made by current methods.

Answer

Failure to thrive may be a presenting sign.

Answer

Vertical transmission from mother to child can occur.

Question 6

A dome-shaped skull with a high forehead in an infant with slight hydrocephalus (Olympian brow) is characteristic of which condition?

Accepted Answer

Congenital syphilis

Answer

Marasmus

Answer

Rickets

Answer

Arnold-Chiari syndrome

Question 7

A 16-month-old boy presents with fever, irritability, and lethargy. Examination reveals nuchal rigidity. He is unvaccinated. CSF Gram stain shows an organism that grows on chocolate agar but not blood agar. The patient has received empirical antibiotics. Which of the following statements regarding the treatment of this condition is FALSE?

Accepted Answer

Fluoroquinolones can be used for treatment.

Answer

Corticosteroids have no role in the treatment of this disease.

Answer

First-line therapy includes ceftriaxone or cefotaxime.

Answer

The duration of therapy is 1-2 weeks.

Question 8

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

Accepted Answer

Treponema pallidum

Answer

Herpes simplex virus

Answer

Hepatitis B virus

Answer

Neisseria gonorrhoeae

Question 9

A 7-month-old child presents with microcephaly. What is the most likely etiology for this clinical presentation?

Accepted Answer

Cytomegalovirus (CMV)

Answer

Toxoplasma

Answer

Rubella

Answer

Mumps

Question 10

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

Accepted Answer

Given to a newborn contact

Answer

Should be given within 24 hours of exposure

Answer

Can be given concurrently with the varicella vaccine

Answer

Administered in established chicken-pox disease

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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