Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 291: Koplik's Spots are seen in which of the following conditions?

A. Rubeola (Correct Answer)
B. Rubella
C. Diphtheria
D. Polio

Explanation: **Explanation:** **Koplik’s spots** are the pathognomonic clinical sign of **Rubeola (Measles)**. They are small, irregular, bluish-white grains on an erythematous base (often described as "grains of salt on a red background") found on the buccal mucosa, typically opposite the lower second molars. They appear during the **prodromal stage**, approximately 48 hours before the characteristic maculopapular rash, and disappear as the rash spreads. **Analysis of Options:** * **A. Rubeola (Correct):** Also known as 9-day measles. Koplik’s spots are a hallmark finding, appearing in up to 70–90% of cases. * **B. Rubella:** Also known as German Measles. It is characterized by **Forschheimer spots** (petechiae on the soft palate), not Koplik’s spots. The rash in Rubella is milder and fades faster. * **C. Diphtheria:** Characterized by a thick, gray, adherent **pseudomembrane** over the tonsils and pharynx. It does not present with enanthems like Koplik’s spots. * **D. Polio:** An enteroviral infection primarily affecting the anterior horn cells of the spinal cord, leading to asymmetrical flaccid paralysis. It has no specific oral mucosal findings. **High-Yield Clinical Pearls for NEET-PG:** * **Sequence of Measles:** Prodrome (Cough, Coryza, Conjunctivitis) → Koplik’s spots → Exanthema (starts behind the ears). * **Vitamin A:** Supplementation is mandatory in Measles management to reduce morbidity and mortality (especially from pneumonia). * **SSPE:** Subacute Sclerosing Panencephalitis is a dreaded late neurological complication of Rubeola. * **Most common complication:** Otitis Media. * **Most common cause of death:** Pneumonia.

Question 292: What is the most common viral cause of acquired aqueductal stenosis?

A. Rubella
B. Mumps (Correct Answer)
C. Toxoplasma
D. Enterovirus

Explanation: **Explanation:** **Correct Answer: B. Mumps** Aqueductal stenosis is a common cause of obstructive hydrocephalus. While most cases are congenital (e.g., X-linked stenosis), acquired cases are often the result of post-inflammatory scarring. **Mumps virus** is the most common viral cause of acquired aqueductal stenosis. The virus has a specific tropism for the ependymal cells lining the ventricular system. Infection leads to **ependymitis**, which results in the sloughing of ependymal cells and subsequent reactive gliosis. This inflammatory process narrows or obliterates the narrowest part of the ventricular system—the **Aqueduct of Sylvius**—leading to non-communicating hydrocephalus, often occurring weeks to months after the initial infection. **Why other options are incorrect:** * **Rubella:** While Congenital Rubella Syndrome (CRS) causes significant CNS involvement (microcephaly, mental retardation), it is more commonly associated with vascular damage and generalized encephalitis rather than isolated aqueductal stenosis. * **Toxoplasma:** *Toxoplasma gondii* is a parasite, not a virus. While it is a classic cause of obstructive hydrocephalus in neonates, it typically causes stenosis via large periventricular calcifications or inflammatory debris. * **Enterovirus:** These are common causes of viral meningitis and encephalitis (e.g., Hand-Foot-Mouth disease, Herpangina) but do not typically lead to the chronic ependymal scarring required to cause aqueductal stenosis. **High-Yield Pearls for NEET-PG:** * **Most common cause of congenital hydrocephalus:** Aqueductal stenosis. * **Most common viral cause of acquired aqueductal stenosis:** Mumps. * **Triad of Congenital Toxoplasmosis:** Hydrocephalus, Chorioretinitis, and Intracranial calcifications (diffuse). * **Mumps complications:** Orchitis (most common extra-salivary site in post-pubertal males), Oophoritis, Pancreatitis, and Aseptic meningitis.

Question 293: Which is the most common organism causing congenital pneumonia?

A. Group B Streptococcus (Correct Answer)
B. Escherichia coli
C. Staphylococcus aureus
D. Salmonella spp.

Explanation: **Explanation:** Congenital pneumonia (pneumonia manifesting within the first 24–72 hours of life) is most commonly caused by organisms colonizing the maternal genitourinary tract. These pathogens are typically transmitted vertically, either via an ascending infection (often following prolonged rupture of membranes) or through aspiration of infected amniotic fluid or vaginal secretions during birth. **Why Group B Streptococcus (GBS) is correct:** *Streptococcus agalactiae* (Group B Strep) remains the **most common cause** of early-onset neonatal sepsis and congenital pneumonia worldwide. It is a commensal in the maternal vaginal flora. In the neonate, it typically presents as a fulminant systemic illness with respiratory distress, often mimicking Hyaline Membrane Disease (HMD) on X-ray. **Why the other options are incorrect:** * **B. Escherichia coli:** This is the **second most common** cause of neonatal sepsis and pneumonia. It is particularly significant in preterm neonates and in regions where GBS prophylaxis is widely implemented. * **C. Staphylococcus aureus:** While a common cause of late-onset (nosocomial) pneumonia or empyema in infants, it is an infrequent cause of immediate congenital pneumonia. * **D. Salmonella spp.:** This is a rare cause of neonatal infection, usually associated with maternal gastroenteritis or contaminated environments, rather than routine vertical transmission. **High-Yield Clinical Pearls for NEET-PG:** 1. **Most common cause of Early Onset Sepsis (EOS):** Group B Streptococcus. 2. **Most common cause of Late Onset Sepsis (LOS):** Coagulase-negative Staphylococci (CONS). 3. **Radiological Mimic:** Congenital pneumonia (especially GBS) can be indistinguishable from Respiratory Distress Syndrome (RDS) on a chest X-ray; both show diffuse reticulogranular patterns and air bronchograms. 4. **Drug of Choice:** For suspected GBS pneumonia, the empirical treatment is a combination of **Ampicillin and Gentamicin**.

Question 294: Large bilateral painless effusions of the knees occurring in late congenital syphilis in patients between ages 8 to 18 are designated as?

A. Clutton's joints (Correct Answer)
B. Ramsey's joints
C. Charcot's joints
D. Mercer's joints

Explanation: **Explanation:** **Clutton’s joints** are a classic manifestation of **late congenital syphilis**, typically appearing between the ages of 8 and 18 years. The condition is characterized by symmetrical, painless swelling (hydrarthrosis) of the joints, most commonly involving the **knees**, though elbows and ankles may also be affected. The underlying pathology is a chronic synovitis with effusion. Despite the significant swelling, there is minimal pain, no redness, and the range of motion is usually preserved. **Analysis of Incorrect Options:** * **Ramsey’s joints:** This is a distractor; there is no recognized medical condition by this name in the context of syphilis or orthopedics. (Note: Not to be confused with Ramsay Hunt syndrome, which involves Herpes Zoster). * **Charcot’s joints (Neuropathic Arthropathy):** This refers to progressive joint destruction due to loss of pain sensation and proprioception. While associated with syphilis, it occurs in **Tertiary Syphilis (Tabes Dorsalis)** in adults, not late congenital syphilis in children. * **Mercer’s joints:** This is a distractor and not a recognized clinical entity in pediatric infectious diseases. **High-Yield Clinical Pearls for NEET-PG:** * **Hutchinson’s Triad:** A hallmark of late congenital syphilis consisting of: 1. Interstitial keratitis, 2. Sensorineural hearing loss (8th nerve deafness), and 3. Hutchinson’s teeth (notched incisors). * **Other Skeletal Signs:** Look for **Saber shins** (anterior bowing of the tibia) and **Higouménakis sign** (thickening of the medial end of the clavicle). * **Early vs. Late:** Clutton’s joints are a "Late" feature (occurring after age 2), whereas **Parrot’s Pseudoparalysis** (due to painful osteochondritis) is an "Early" feature seen in infants.

Question 295: What is the most common cause of fetal loss?

A. Syphilis
B. Herpes genitalis (Correct Answer)
C. Rubella
D. Measles

Explanation: **Explanation:** The correct answer is **Herpes genitalis (HSV-2)**. While many intrauterine infections can cause fetal complications, Herpes Simplex Virus (HSV) infection during pregnancy—especially primary infection—is associated with the highest risk of fetal loss. **Why Herpes genitalis is correct:** Primary maternal infection with HSV-2 during the first or second trimester is associated with a significantly increased risk of spontaneous abortion (fetal loss). If the infection occurs later in pregnancy, it leads to preterm labor or neonatal herpes. The high viral load and lack of maternal antibodies during a primary episode facilitate hematogenous spread to the placenta, leading to fetal demise. **Analysis of Incorrect Options:** * **Syphilis (*Treponema pallidum*):** While a major cause of stillbirth (fetal death after 20 weeks) and hydrops fetalis, it is statistically less common as a cause of early spontaneous abortion compared to HSV. * **Rubella:** Infection during the first trimester primarily causes **Congenital Rubella Syndrome (CRS)** characterized by malformations (cataracts, PDA, deafness). While it can cause fetal loss, the incidence of teratogenicity is higher than the rate of abortion. * **Measles:** Measles during pregnancy is associated with maternal morbidity and an increased risk of prematurity or low birth weight, but it is not a classic "TORCH" agent and is a rare cause of fetal loss. **NEET-PG High-Yield Pearls:** * **Most common route of Neonatal HSV:** Through the birth canal (85-90%). * **Highest risk of transmission:** Primary maternal infection at the time of delivery (50% risk) vs. recurrent infection (<3% risk). * **Treatment of choice:** Acyclovir is safe and indicated for pregnant women with primary or recurrent genital herpes. * **Delivery:** Cesarean section is indicated if active genital lesions or prodromal symptoms are present at the time of labor.

Question 296: Which of the following is true about roseola infantum?

A. Defervescence follows the rash
B. Caused by HHV 6 and 7 (Correct Answer)
C. Slapped cheek appearance is seen
D. Otitis media is a common complication

Explanation: ### Explanation **Roseola Infantum**, also known as **Exanthema Subitum** or Sixth Disease, is a common viral febrile illness of early childhood (typically 6–36 months of age). **1. Why Option B is Correct:** Roseola is primarily caused by **Human Herpesvirus 6 (HHV-6)**, and less frequently by **HHV-7**. These viruses are lymphotropic and remain latent in the body after primary infection. **2. Analysis of Incorrect Options:** * **Option A:** In Roseola, the classic clinical hallmark is that the **rash appears after defervescence** (the fever disappears). The child typically has a high-grade fever (often >40°C) for 3–5 days; as the fever abruptly drops, a maculopapular rash emerges. * **Option C:** A "slapped cheek" appearance is the characteristic rash of **Erythema Infectiosum** (Fifth Disease), caused by **Parvovirus B19**. * **Option D:** While otitis media can occur, the most common and high-yield complication associated with Roseola infantum is **Febrile Seizures**, occurring in approximately 10–15% of cases due to the rapid rise in temperature. **3. NEET-PG High-Yield Clinical Pearls:** * **Nagayama Spots:** Small erythematous papules on the soft palate and uvula (seen in some patients before the skin rash). * **Rash Characteristics:** The rash is typically rose-pink, non-pruritic, starts on the **trunk**, and spreads to the neck and extremities (centrifugal spread). * **Age Group:** Most common cause of a febrile rash in an infant under 2 years of age. * **Treatment:** Supportive (antipyretics); the disease is usually self-limiting.

Question 297: A 15-year-old boy presents with a two-day history of fever, altered sensorium, and purpuric rash. On examination, the patient is stuporous with a blood pressure of 90/60 mm Hg and extensive palpable purpura on the legs. Which of the following is the most appropriate initial choice of antibiotic?

A. Vancomycin
B. Penicillin G
C. Ciprofloxacin
D. Ceftriaxone (Correct Answer)

Explanation: **Explanation:** The clinical presentation of fever, altered sensorium, and a purpuric rash in an adolescent is highly suggestive of **Meningococcemia** (caused by *Neisseria meningitidis*). The presence of purpura and hypotension (90/60 mm Hg) indicates a medical emergency, likely progressing toward Waterhouse-Friderichsen syndrome. **1. Why Ceftriaxone is correct:** In cases of suspected bacterial meningitis or meningococcemia, **Ceftriaxone** (a third-generation cephalosporin) is the empirical drug of choice. It provides excellent coverage against *N. meningitidis*, *Streptococcus pneumoniae*, and *Haemophilus influenzae*. It has superior CSF penetration and a longer half-life, making it ideal for rapid stabilization in a suspected septic patient. **2. Why other options are incorrect:** * **Vancomycin:** While used empirically for resistant *S. pneumoniae* or MRSA, it does not cover *N. meningitidis* effectively as a monotherapy. * **Penicillin G:** Historically the drug of choice, but it is no longer used empirically due to increasing resistance and the need for a broader spectrum until the pathogen is confirmed. * **Ciprofloxacin:** Used primarily for **chemoprophylaxis** in close contacts of a patient with meningococcal disease, not for the acute treatment of the disease itself. **Clinical Pearls for NEET-PG:** * **Drug of choice for Chemoprophylaxis:** Rifampicin (most common), Ciprofloxacin (single dose), or Ceftriaxone (in pregnancy). * **Glass Test:** Non-blanching purpuric rashes are a hallmark of meningococcal septicaemia. * **Initial Management:** Always prioritize ABCs (Airway, Breathing, Circulation) and administer the first dose of antibiotics within the "Golden Hour" to reduce mortality.

Question 298: CHARGE syndrome does not include which of the following abnormalities?

A. Coloboma of the eye
B. Heart abnormalities
C. Ear abnormalities
D. Renal abnormalities (Correct Answer)

Explanation: **Explanation:** **CHARGE syndrome** is a recognizable genetic pattern of birth defects caused primarily by mutations in the **CHD7 gene** on chromosome 8. The diagnosis is based on a specific mnemonic where each letter represents a major clinical feature. 1. **Why "Renal abnormalities" is the correct answer:** While renal anomalies (like hydronephrosis or renal hypoplasia) can occasionally occur in children with CHARGE, they are **not** part of the core diagnostic criteria or the classic mnemonic. In the context of NEET-PG questions, "R" in CHARGE specifically stands for **Retardation of growth and development**, not Renal abnormalities. 2. **Analysis of Incorrect Options:** * **A. Coloboma of the eye:** This is the "C" in CHARGE. It typically affects the retina or iris and is a major diagnostic criterion. * **B. Heart abnormalities:** This is the "H". Common defects include Tetralogy of Fallot, PDA, and VSD. * **C. Ear abnormalities:** This is the "E". It includes characteristic "cup-shaped" ears, hearing loss, and semicircular canal hypoplasia (vestibular issues). **Clinical Pearls for NEET-PG:** * **Mnemonic Breakdown:** * **C:** Coloboma * **H:** Heart defects * **A:** Atresia choanae (Choanal atresia) * **R:** Retardation of growth/development * **G:** Genitourinary anomalies (e.g., micropenis, undescended testes due to hypogonadotropic hypogonadism) * **E:** Ear abnormalities/Deafness * **Genetic Marker:** Mutations in the **CHD7 gene** (Chromodomain helicase DNA-binding protein 7). * **High-Yield Tip:** If a question asks for the most common feature, **Coloboma** and **Choanal Atresia** are the most specific major criteria.

Question 299: A 2-year-old child has a Mantoux test reading of 12 mm after 48 hours. What is the appropriate management in this case?

A. Anti-TB drugs should be started even if chest X-ray and hemogram are normal. (Correct Answer)
B. Treatment should be started only if chest X-ray and hemogram are suggestive.
C. Wait until overt signs of TB appear.
D. No treatment is required.

Explanation: ### Explanation **1. Why Option A is Correct:** In pediatric practice, particularly in TB-endemic regions like India, a Mantoux test (Tuberculin Skin Test) result of **≥10 mm** is considered positive. In a child under 5 years of age, a positive Mantoux test is a significant indicator of **Latent Tuberculosis Infection (LTBI)** or active disease. According to the **Revised National TB Control Program (RNTCP/NTEP) guidelines**, if a child has a positive Mantoux test and is symptomatic, they are treated for active TB. However, if the child is asymptomatic but has a positive Mantoux, they are still at a high risk of progression to severe forms of TB (like TBM or miliary TB) due to their immature immune system. Therefore, even if the chest X-ray and hemogram are normal, the child must be started on **Isoniazid (INH) prophylaxis** (usually for 6 months) to prevent the development of active disease. **2. Why Other Options are Incorrect:** * **Option B:** Waiting for X-ray changes ignores the concept of Latent TB. In young children, the goal is to prevent the progression of infection to disease. * **Option C:** Waiting for overt signs is dangerous in toddlers, as they can rapidly develop life-threatening disseminated tuberculosis. * **Option D:** Ignoring a 12 mm induration in a 2-year-old is a clinical error, as it indicates a high risk of future reactivation. **3. Clinical Pearls for NEET-PG:** * **Cut-off Values:** ≥5 mm is positive in HIV+ children or close contacts of active cases; ≥10 mm is positive for all other children. * **Reading:** The test is read between **48–72 hours** by measuring the **transverse diameter of induration** (not erythema) using the Pen-and-Ruler method. * **Window Period:** It takes 2–12 weeks after infection for the Mantoux test to become positive. * **BCG Effect:** A previous BCG vaccination usually produces an induration <10 mm; any reading >10 mm should be attributed to TB infection rather than the vaccine.

Question 300: All of the following are part of the classic triad for congenital rubella syndrome, except:

A. Sensory neural deafness
B. Cataract
C. Patent ductus arteriosus
D. Micrognathia (Correct Answer)

Explanation: The **Gregg Triad** (Classic Triad) of Congenital Rubella Syndrome (CRS) consists of ocular, auditory, and cardiac defects. **Explanation of the Correct Answer:** **D. Micrognathia** is the correct answer because it is **not** part of the classic triad. Micrognathia (a small jaw) is more commonly associated with other genetic conditions, such as Pierre Robin sequence or Trisomy 18 (Edwards syndrome), rather than CRS. **Explanation of Incorrect Options:** * **A. Sensorineural Deafness:** This is the **most common** manifestation of CRS (occurring in about 80% of cases). It is often bilateral and may be the only presenting sign in late-onset cases. * **B. Cataract:** Ocular defects are a hallmark of the triad. While "pearlescent" nuclear cataracts are classic, other findings include infantile glaucoma and "salt-and-pepper" retinopathy. * **C. Patent Ductus Arteriosus (PDA):** This is the most common cardiac defect in CRS. Another high-yield cardiac association is **Peripheral Pulmonary Artery Stenosis**. **High-Yield Clinical Pearls for NEET-PG:** * **Timing:** The risk of malformation is highest if the mother is infected during the **first trimester** (especially the first 8 weeks). * **Dermal Erythropoiesis:** Look for the **"Blueberry muffin rash"** (also seen in CMV). * **Expanded CRS:** Beyond the triad, look for microcephaly, radiolucent bone disease (celery stalking appearance), and hepatosplenomegaly. * **Diagnosis:** Presence of **Rubella-specific IgM** in the newborn or persistence of IgG beyond 6–12 months. * **Prevention:** Live attenuated **RA 27/3 vaccine**. Note: It is contraindicated in pregnancy; women should avoid conception for 1 month post-vaccination.

Practice by Chapter

Vaccine-Preventable Diseases

Practice Questions

Immunization Schedule

Practice Questions

Common Childhood Infections

Practice Questions

Pediatric HIV

Practice Questions

Congenital Infections

Practice Questions

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

Practice Questions

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free