Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 41: What is the estimated risk of mother-to-child transmission of HIV?

A. 25% (Correct Answer)
B. 50%
C. 60%
D. 75%

Explanation: **Explanation:** The risk of Mother-to-Child Transmission (MTCT) of HIV, in the **absence of any medical intervention** (antiretroviral therapy, elective cesarean section, or avoidance of breastfeeding), is estimated to be between **25% and 30%**. Transmission can occur during three distinct periods: 1. **In utero (Transplacental):** ~5–10% 2. **Intrapartum (During labor/delivery):** ~15% (This is the period of highest risk due to exposure to infected maternal blood and cervicovaginal secretions). 3. **Postpartum (Breastfeeding):** ~5–15%. **Analysis of Options:** * **Option A (25%):** This is the standard accepted figure for vertical transmission risk without intervention. With modern Highly Active Antiretroviral Therapy (HAART) and a suppressed viral load, this risk can be reduced to **less than 1%**. * **Options B, C, and D (50%, 60%, 75%):** These values significantly overestimate the biological efficiency of HIV transmission. Even without treatment, the majority of infants born to HIV-positive mothers do not contract the virus. **High-Yield Clinical Pearls for NEET-PG:** * **Most common route of pediatric HIV:** Vertical transmission (MTCT). * **Diagnosis in infants:** HIV DNA PCR is the gold standard (performed at birth, 6 weeks, 6 months). Antibody tests (ELISA) are unreliable until **18 months** due to the persistence of maternal IgG antibodies. * **Prophylaxis:** Nevirapine is typically administered to the newborn for 6 weeks. * **Breastfeeding:** In India, exclusive breastfeeding is recommended for the first 6 months if the mother is on ART, followed by complementary feeding. Mixed feeding should be strictly avoided as it increases the risk of transmission.

Question 42: A 2-month-old child born to an HIV-positive mother is under your care. Which of the following prophylactic therapies should be considered for this child?

A. Monthly evaluation for Kaposi sarcoma
B. Prophylaxis against Pneumocystis jiroveci pneumonia (Correct Answer)
C. Vitamin C supplementation
D. Oral polio virus vaccine

Explanation: **Explanation:** The correct answer is **B. Prophylaxis against Pneumocystis jiroveci pneumonia (PCP).** **Why it is correct:** *Pneumocystis jiroveci* pneumonia (PCP) is the most common opportunistic infection in HIV-infected infants, with a peak incidence between **2 and 6 months of age**. Because HIV-exposed infants are at high risk of rapid disease progression and severe respiratory failure from PCP, the WHO and National AIDS Control Organization (NACO) guidelines recommend starting **Cotrimoxazole (TMP-SMX) prophylaxis** for all HIV-exposed infants starting at **4–6 weeks of age**. This is continued until the infant is confirmed to be HIV-negative or, if positive, until they are clinically stable on ART with improved CD4 counts. **Why the other options are incorrect:** * **Option A:** Kaposi sarcoma is rare in the pediatric population and is not a routine screening requirement for infants. * **Option C:** While nutrition is important, Vitamin C supplementation is not a specific prophylactic therapy for HIV-exposed infants. * **Option D:** Oral Polio Vaccine (OPV) is a **live-attenuated vaccine**. In HIV-exposed or infected children, live vaccines are generally avoided if the child is severely symptomatic or immunocompromised. In many countries, Inactivated Polio Vaccine (IPV) is preferred to avoid the risk of vaccine-associated paralytic polio (VAPP). **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice for PCP Prophylaxis:** Cotrimoxazole (Trimethoprim-Sulfamethoxazole). * **Timing:** Start at 4–6 weeks of age in all HIV-exposed infants. * **Diagnosis in Infants:** HIV DNA PCR (at 6 weeks) is the gold standard for infants <18 months, as maternal IgG antibodies cross the placenta, making ELISA unreliable. * **Breastfeeding:** Exclusive breastfeeding for the first 6 months is recommended if the mother is on ART, followed by complementary feeding. Mixed feeding should be avoided.

Question 43: A 5-year-old boy presents to the emergency room after a dog bite on his right forearm. The laceration is small, irregular, and superficial, and bleeding has stopped. The child has a normal neuromuscular examination and intact perfusion. What is the most appropriate management for this injury?

A. Irrigation and antimicrobial prophylaxis
B. Tetanus booster immunization and tetanus toxoid in the wound
C. Copious irrigation (Correct Answer)
D. Primary rabies vaccination for the child

Explanation: **Explanation:** The primary goal in managing any animal bite is the prevention of infection (both bacterial and viral). **1. Why "Copious Irrigation" is correct:** The single most effective step in reducing the risk of infection following a dog bite is **copious irrigation** with normal saline or sterile water. This mechanical debridement flushes out saliva, debris, and pathogens (like *Pasteurella multocida*) from the wound. In the management of rabies-prone bites, immediate wound washing with soap and water for at least 15 minutes is the most critical initial step recommended by WHO and national guidelines. **2. Why other options are incorrect:** * **Option A:** While antimicrobial prophylaxis (Amoxicillin-Clavulanate) is often indicated for high-risk bites (cat bites, hand wounds, or immunocompromised patients), it is secondary to local wound care. * **Option B:** Tetanus prophylaxis is essential if the child is under-immunized, but "tetanus toxoid in the wound" is medically incorrect; vaccines are administered intramuscularly. * **Option C:** Rabies post-exposure prophylaxis (PEP) depends on the dog's vaccination status and the category of the bite. However, even if PEP is required, it never supersedes immediate local wound toilet. **Clinical Pearls for NEET-PG:** * **Organism:** *Pasteurella multocida* is the most common aerobic organism in dog/cat bites. *Capnocytophaga canimorsus* is a concern in splenectomized patients. * **Drug of Choice:** Amoxicillin-Clavulanate (covers anaerobes and *Pasteurella*). * **Suturing:** Dog bites on the extremities are generally left open (healing by secondary intention) to prevent abscess formation, unless they are on the face (for cosmesis). * **Rabies Categories:** Category I (touching/licking intact skin) needs no PEP; Category II (nibbling, minor scratches) needs vaccine; Category III (transdermal bites/licks on broken skin) needs vaccine + Rabies Immunoglobulin (RIG).

Question 44: A 16-day-old infant presents with fever, irritability, poor feeding, and a bulging fontanel. Spinal fluid demonstrates Gram-positive rods. Which of the following is the most likely diagnosis?

A. Listeria monocytogenes (Correct Answer)
B. Group A streptococci
C. Group B streptococci
D. Streptococcus pneumoniae

Explanation: **Explanation:** The clinical presentation of fever, irritability, poor feeding, and a bulging fontanel in a 16-day-old neonate is classic for **neonatal meningitis**. The definitive clue in this question is the Gram stain result: **Gram-positive rods**. **Why Listeria monocytogenes is correct:** *Listeria monocytogenes* is a unique neonatal pathogen because it is a **Gram-positive bacilli (rod)**. It is the third most common cause of neonatal sepsis and meningitis, typically transmitted via the placenta (early-onset) or during vaginal delivery (late-onset). In the context of neonatal meningitis, any mention of "Gram-positive rods" or "coccobacilli" specifically points to *Listeria*. **Why the other options are incorrect:** * **Group B Streptococci (GBS):** While *S. agalactiae* (GBS) is the **most common** cause of neonatal meningitis, it appears as **Gram-positive cocci in chains**, not rods. * **Group A Streptococci:** This is an uncommon cause of neonatal meningitis and would also appear as Gram-positive cocci. * **Streptococcus pneumoniae:** This is a leading cause of meningitis in older infants (usually >3 months) and adults. On Gram stain, it appears as **Gram-positive lancet-shaped diplococci**. **NEET-PG High-Yield Pearls:** 1. **Top 3 causes of Neonatal Meningitis:** 1. Group B Streptococcus (most common), 2. *E. coli* (Gram-negative rod), 3. *Listeria monocytogenes*. 2. **Listeria Characteristics:** It exhibits **"tumbling motility"** at 25°C and can grow at cold temperatures (cold enrichment). 3. **Empiric Treatment:** Because cephalosporins (like Cefotaxime) do not cover *Listeria*, **Ampicillin** must always be added to the empiric regimen for neonatal meningitis. 4. **Granulomatosis Infantiseptica:** A severe, disseminated form of early-onset neonatal listeriosis characterized by internal pyogenic granulomas.

Question 45: Which of the following is NOT a feature of Congenital rubella syndrome?

A. Congenital Cataract
B. Microphthalmia
C. Salt and pepper retinitis
D. Anterior Uveitis (Correct Answer)

Explanation: **Explanation:** Congenital Rubella Syndrome (CRS) is a classic TORCH infection characterized by a triad of ocular, cardiac, and auditory defects. The correct answer is **Anterior Uveitis** because it is not a typical feature of CRS; instead, it is more commonly associated with other congenital infections like Syphilis or Toxoplasmosis. **Analysis of Options:** * **Congenital Cataract (Option A):** This is a hallmark ocular finding in CRS, often described as "pearly white" and usually bilateral. It occurs due to the virus's persistence in the lens fiber. * **Microphthalmia (Option B):** This refers to abnormally small eyes and is a well-documented structural defect in infants with CRS, often occurring alongside cataracts. * **Salt and Pepper Retinitis (Option C):** This is the **most common** ocular manifestation of CRS. It is characterized by mottled pigmentation of the retina and typically does not affect vision significantly. * **Anterior Uveitis (Option D):** While CRS involves many parts of the eye, primary inflammation of the anterior uvea is not a standard feature. **Clinical Pearls for NEET-PG:** 1. **Gregg’s Triad:** Cataract, Sensorineural Hearing Loss (most common overall feature), and Congenital Heart Disease (PDA is most common; Peripheral Pulmonary Artery Stenosis is most specific). 2. **Dermal Erythropoiesis:** Presents as the "Blueberry muffin rash." 3. **Timing:** The risk of malformations is highest if the mother is infected during the **first trimester** (especially the first 8 weeks). 4. **Diagnosis:** Confirmed by Rubella-specific IgM antibodies in the neonate or persistence of IgG beyond 6–12 months.

Question 46: True about Palivizumab are all, EXCEPT:

A. Used by intramuscular route
B. Used in treatment of RSV infection (Correct Answer)
C. Adverse effects include upper respiratory tract infection
D. None of the above

Explanation: **Explanation:** **Palivizumab** is a humanized monoclonal antibody directed against the **F (fusion) protein** of the Respiratory Syncytial Virus (RSV). **Why Option B is the Correct Answer (The Exception):** Palivizumab is strictly used for **prophylaxis (prevention)**, not for the treatment of an established RSV infection. Clinical trials have shown that it does not decrease viral load or improve the clinical outcome once the patient has already developed RSV bronchiolitis or pneumonia. **Analysis of Other Options:** * **Option A:** Palivizumab is administered via the **intramuscular (IM)** route, typically in the anterolateral aspect of the thigh. It is given in monthly doses during the RSV season (usually up to 5 doses). * **Option C:** Common adverse effects include fever, rash, and **upper respiratory tract infections**. While it prevents severe lower respiratory tract disease, patients can still develop mild upper respiratory symptoms. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Inhibits the fusion of the virus to the host cell membrane by targeting the F-protein. * **Indications (AAP Guidelines):** 1. Preterm infants born at **<29 weeks** gestation. 2. Infants with **Chronic Lung Disease (CLD)** of prematurity. 3. Infants with hemodynamically significant **Congenital Heart Disease (CHD)**. * **Ribavirin:** Unlike Palivizumab, Ribavirin (aerosolized) is the antiviral agent used for the *treatment* of severe RSV, though its use is now limited to specific high-risk cases. * **RSV Season:** Prophylaxis is usually initiated at the onset of the RSV season (late fall/winter).

Question 47: Following splenectomy in children, which one of the following is recommended?

A. Hepatitis B vaccination
B. Typhoid vaccination
C. Pneumococcal vaccination (Correct Answer)
D. Regular follow-up

Explanation: **Explanation:** The spleen plays a critical role in the immune system by filtering blood-borne pathogens and producing opsonins (like tuftsin and properdin). Post-splenectomy, patients are at a lifelong risk of **Overwhelming Post-Splenectomy Infection (OPSI)**, primarily caused by **encapsulated organisms**. **Why Pneumococcal Vaccination is Correct:** *Streptococcus pneumoniae* is the most common cause of OPSI, accounting for 50–90% of cases. Therefore, immunization against Pneumococcus is mandatory. Ideally, vaccines should be administered **at least 2 weeks before** elective splenectomy or **2 weeks after** emergency surgery to ensure an adequate immune response. **Analysis of Incorrect Options:** * **Hepatitis B & Typhoid Vaccination:** While important in general pediatric schedules, these are not specifically mandated by the loss of splenic function. The spleen is not the primary site for clearing these specific pathogens. * **Regular Follow-up:** While follow-up is necessary for monitoring, it is a general management step and does not provide the specific immunological protection required to prevent life-threatening sepsis. **High-Yield Clinical Pearls for NEET-PG:** 1. **The "Big Three" Vaccines:** Post-splenectomy patients must receive vaccines against *Streptococcus pneumoniae*, *Haemophilus influenzae* type b (Hib), and *Neisseria meningitidis*. 2. **Antibiotic Prophylaxis:** Daily oral **Penicillin V** prophylaxis is recommended, especially in children under 5 years of age or for at least 2 years post-surgery. 3. **Timing:** If the surgery is elective, vaccinate 14 days prior. If emergency, vaccinate 14 days post-op (to avoid the period of post-surgical "immunological stun"). 4. **Annual Flu Shot:** Recommended to prevent secondary bacterial pneumonia.

Question 48: Which of the following is a complication of Down syndrome?

A. Ventricular Septal Defect (VSD)
B. Acute Lymphoblastic Leukemia (ALL)
C. Hypothyroidism
D. All of the above (Correct Answer)

Explanation: **Explanation:** Down syndrome (Trisomy 21) is a multisystemic chromosomal disorder characterized by a wide array of associated anomalies and complications. The correct answer is **"All of the above"** because individuals with Down syndrome have a significantly higher predisposition to cardiac, hematological, and endocrine pathologies compared to the general population. * **Ventricular Septal Defect (VSD):** While **Atrioventricular Septal Defect (AVSD/Endocardial Cushion Defect)** is the most common cardiac lesion in Down syndrome (approx. 40%), VSD is the second most common. Congenital heart disease (CHD) occurs in nearly 50% of these patients. * **Acute Lymphoblastic Leukemia (ALL):** Children with Down syndrome have a 10–20 fold increased risk of developing leukemia. While **Acute Megakaryoblastic Leukemia (AML-M7)** is highly specific and more common in children *under* 3 years, **ALL** is actually more common in children with Down syndrome *over* the age of 3. * **Hypothyroidism:** Endocrine dysfunction is frequent, with congenital or acquired (autoimmune) hypothyroidism being the most common. Routine screening of thyroid-stimulating hormone (TSH) levels is a standard of care. **High-Yield Clinical Pearls for NEET-PG:** * **Most common cause of mental retardation:** Down syndrome (Genetic/Chromosomal). * **Gastrointestinal:** Duodenal atresia ("Double bubble" sign) and Hirschsprung disease are classic associations. * **Musculoskeletal:** Atlanto-axial instability (risk of spinal cord compression). * **Dermatoglyphics:** Simian crease (single palmar crease) and increased ulnar loops. * **Early-onset Alzheimer’s disease:** Due to the APP gene located on chromosome 21.

Question 49: According to WHO staging, what stage is assigned to an HIV-infected child presenting with parotid enlargement?

A. Stage 1
B. Stage 2 (Correct Answer)
C. Stage 3
D. Stage 4

Explanation: **Explanation:** The WHO Clinical Staging of HIV in children is categorized based on clinical severity and the degree of immunosuppression. **Correct Option: B (Stage 2)** According to the WHO classification for children (<15 years), **Persistent Parotid Enlargement** is a characteristic feature of **Clinical Stage 2 (Mild Disease)**. This stage typically involves "mild" symptoms that are not life-threatening but indicate disease progression. Other common manifestations in Stage 2 include unexplained persistent hepatosplenomegaly, papular pruritic eruptions, extensive wart infections, and recurrent upper respiratory tract infections (e.g., sinusitis or otitis media). **Why other options are incorrect:** * **Stage 1:** This stage represents **Asymptomatic** infection. The only clinical finding allowed here is Persistent Generalized Lymphadenopathy (PGL). Parotid enlargement is considered a symptomatic progression beyond Stage 1. * **Stage 3:** This stage involves **Advanced** symptoms such as unexplained moderate malnutrition, persistent diarrhea, oral candidiasis, or pulmonary tuberculosis. * **Stage 4:** This stage represents **Severe (AIDS-defining)** illness, including conditions like Pneumocystis pneumonia (PCP), esophageal candidiasis, or HIV wasting syndrome. **Clinical Pearls for NEET-PG:** * **Parotid Enlargement:** In HIV-infected children, this is often due to **Lymphocytic Interstitial Pneumonitis (LIP)** or benign lymphoepithelial cysts. * **LIP vs. TB:** LIP is a Stage 3 condition, but isolated parotid enlargement remains Stage 2. * **Most Common Opportunistic Infection:** In children, it is often *Pneumocystis jirovecii* (Stage 4), which is why Co-trimoxazole prophylaxis is vital. * **Diagnosis:** For children <18 months, DNA-PCR (virological testing) is required; for >18 months, standard Antibody testing (ELISA) is used.

Question 50: Which of the following is NOT a sonographic finding of fetal syphilis?

A. Hepatomegaly
B. Lymphadenopathy (Correct Answer)
C. Placentomegaly
D. Ascites/hydrops

Explanation: **Explanation:** Congenital syphilis is caused by the transplacental transmission of *Treponema pallidum*. The sonographic findings of fetal syphilis are primarily a reflection of fetal inflammatory response, severe anemia, and hepatic dysfunction. **Why Lymphadenopathy is the correct answer:** While lymphadenopathy is a classic physical exam finding in **neonates** with early congenital syphilis (presenting as generalized swelling or "snuffles"), it is **not** a detectable or characteristic finding on **prenatal ultrasound**. Fetal sonography focuses on organomegaly and fluid distribution rather than discrete fetal lymph node visualization. **Analysis of Incorrect Options:** * **Hepatomegaly (Option A):** This is the **most common** and often the earliest sonographic sign of fetal syphilis. It results from direct treponemal infiltration of the liver and extramedullary hematopoiesis. * **Placentomegaly (Option C):** A thick, enlarged placenta (typically >4-5 cm in the second/third trimester) is a hallmark of syphilis. It occurs due to villous edema and inflammation (villitis). * **Ascites/Hydrops (Option D):** As the disease progresses, hepatic dysfunction (leading to hypoalbuminemia) and severe anemia lead to fetal hydrops, characterized by ascites, pleural effusion, and skin edema. **NEET-PG High-Yield Pearls:** * **Triad of Fetal Syphilis:** Hepatomegaly, Placentomegaly, and Polyhydramnios. * **Screening:** All pregnant women should be screened at the first prenatal visit with non-treponemal tests (VDRL/RPR). * **Treatment of Choice:** Parenteral **Penicillin G** is the only treatment documented to be effective for preventing maternal transmission to the fetus and treating fetal infection. * **Jarisch-Herxheimer Reaction:** Pregnant women treated for syphilis must be monitored for this reaction, as it can precipitate preterm labor or fetal distress.

Practice by Chapter

Vaccine-Preventable Diseases

Practice Questions

Immunization Schedule

Practice Questions

Common Childhood Infections

Practice Questions

Pediatric HIV

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Congenital Infections

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Fever in Infants and Children

Practice Questions

Meningitis and Encephalitis

Practice Questions

Respiratory Tract Infections

Practice Questions

Gastrointestinal Infections

Practice Questions

Parasitic Infections

Practice Questions

Tuberculosis in Children

Practice Questions

Opportunistic Infections

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