Infectious Diseases Practice Questions

Q: What is the percentage of coincidence between a sore throat and acute rheumatic fever?

3%. **Explanation:** Acute Rheumatic Fever (ARF) is a delayed, non-suppurative sequela of an upper respiratory tract infection caused by **Group A Beta-Hemolytic Streptococcus (GABHS)**. The relationship between the initial infection and the development of ARF is a classic high-yield concept in Pediatrics. **1. Why 3% is Correct:** Epidemiological studies have established that in an **untreated** or inadequately treated episode of GABHS pharyngitis (sore throat), approximately **3%** of individuals will go on to develop Acute Rheumatic Fever. This percentage remains the gold standard in medical literature for endemic populations. In contrast, during "sporadic" outbreaks in developed nations, the incidence may drop significantly below 1%, but for examination purposes, the 3% rule is the recognized benchmark. **2. Analysis of Incorrect Options:** * **5%, 7%, and 9%:** These values overestimate the attack rate. While GABHS is a common cause of sore throat, the progression to ARF requires a specific combination of host genetic susceptibility and the rheumatogenic potential of the specific streptococcal strain (e.g., M-types 1, 3, 5, 6, 18). **3. Clinical Pearls for NEET-PG:** * **The Latent Period:** ARF typically develops **2–4 weeks** after the initial sore throat. * **Prevention:** Primary prevention (treating the sore throat with Penicillin within 9 days of onset) can almost entirely prevent the development of ARF. * **Skin Infections:** Unlike Post-Streptococcal Glomerulonephritis (PSGN), **ARF does not follow streptococcal skin infections (impetigo/pyoderma).** It only follows pharyngeal infections. * **Diagnosis:** Diagnosis is clinical, based on the **Revised Jones Criteria (2015)**, which now categorizes patients into low-risk and moderate/high-risk populations.

Q: What is the standard treatment for Chlamydia pneumoniae infection?

Erythromycin. **Explanation:** *Chlamydia pneumoniae* is an obligate intracellular bacterium and a common cause of atypical pneumonia in children and adolescents. Because it lacks a traditional peptidoglycan cell wall, it is inherently resistant to beta-lactam antibiotics. **Why Erythromycin is correct:** Macrolides, such as **Erythromycin**, are the treatment of choice for *Chlamydia* species. They work by inhibiting protein synthesis by binding to the 50S ribosomal subunit. In pediatric practice, while Erythromycin is the classic answer, newer macrolides like Azithromycin or Clarithromycin are often preferred due to better GI tolerance and simpler dosing schedules. For older children (>8 years), Tetracyclines (Doxycycline) are also an effective alternative. **Why the other options are incorrect:** * **Ceftriaxone (Cephalosporin) & Penicillin:** These are beta-lactam antibiotics that act by inhibiting cell wall synthesis. Since *Chlamydia* does not have a typical bacterial cell wall, these drugs are completely ineffective. * **Sulphonamides:** While sulfonamides interfere with folic acid synthesis and are used for some intracellular organisms (like *Nocardia*), they are not the standard of care for *Chlamydia pneumoniae* and show poor clinical efficacy compared to macrolides. **High-Yield Clinical Pearls for NEET-PG:** * **Atypical Presentation:** Look for a "subacute" onset with a prominent, non-productive cough, low-grade fever, and "dissociation" (physical signs on chest X-ray are much worse than the clinical appearance of the patient). * **Chlamydia trachomatis (Infants):** Causes "staccato cough" and peripheral eosinophilia in neonates (usually 2–12 weeks old). Erythromycin is also the drug of choice here. * **Drug Side Effect:** Be aware that Erythromycin use in neonates is associated with an increased risk of **Infantile Hypertrophic Pyloric Stenosis (IHPS)**.

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

Clutton's joints. **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.

Q: Which of the following is true about roseola infantum?

Caused by HHV 6 and 7. ### 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.

Q: What is the treatment of varicella in an immunocompetent host?

Prevention of complications. ### **Explanation** The correct answer is **C. Prevention of complications**. **1. Why "Prevention of complications" is correct:** In an **immunocompetent host** (especially children), Varicella (Chickenpox) is typically a self-limiting disease. The primary goal of management is supportive care to prevent secondary bacterial infections (most commonly by *Staphylococcus aureus* or *Streptococcus pyogenes*) and other complications. This includes maintaining hygiene, trimming fingernails to prevent scratching, and using calamine lotion or antihistamines for pruritus. Antiviral therapy is generally not mandatory for healthy children as the benefit is marginal. **2. Why the other options are incorrect:** * **A. Acyclovir:** While Acyclovir can be used, it is **not routine** for all immunocompetent hosts. It is specifically indicated if the patient is >12 years old, has chronic cutaneous/pulmonary disorders, or is on long-term salicylate/steroid therapy. * **B. Acyclovir and vaccination:** Vaccination is a preventive measure (primary prophylaxis) and is not used as a treatment modality once the infection has manifested. * **C. Immunoglobulin (VZIG):** This is used for **post-exposure prophylaxis** in high-risk individuals (e.g., neonates, pregnant women, or immunocompromised patients) who have been exposed to the virus, not as standard treatment for an active infection in a healthy host. **3. Clinical Pearls for NEET-PG:** * **Tzanck Smear:** Shows **Multinucleated Giant Cells** (common to HSV and VZV). * **Dew-drop on a rose petal:** Classic description of the varicella vesicle on an erythematous base. * **Pleomorphism:** The hallmark of chickenpox where lesions in all stages (papules, vesicles, crusts) are seen simultaneously. * **Congenital Varicella Syndrome:** Highest risk if the mother is infected between **8–20 weeks** of gestation; characterized by limb hypoplasia and cicatricial skin scarring.

Q: What is the recommended treatment for an infant born to a mother with active tuberculosis?

Isoniazid prophylaxis. **Explanation:** The management of a neonate born to a mother with active tuberculosis (TB) focuses on preventing the high risk of primary infection and progression to disseminated disease (like TB meningitis) in the infant. **Why Option A is Correct:** According to the **National Tuberculosis Elimination Program (NTEP)** and WHO guidelines, if a mother has active pulmonary TB, the neonate should be started on **Isoniazid (INH) prophylaxis** at a dose of **5 mg/kg/day for 6 months**. This is because the infant is considered a "high-risk contact." BCG vaccination should be deferred until the completion of the 6-month INH course. After 6 months, if the infant is asymptomatic and the Mantoux test/Chest X-ray is negative, INH is stopped and BCG is administered. **Why Other Options are Incorrect:** * **Option B:** Incorrect because neonates have immature cell-mediated immunity; exposure without prophylaxis leads to a very high rate of progression to active disease. * **Options C & D:** These represent "Treatment" rather than "Prophylaxis." Full multi-drug therapy is only indicated if the neonate shows clinical signs of **Congenital TB** or has a positive evaluation (e.g., abnormal Chest X-ray or positive gastric aspirate for AFB). **High-Yield Clinical Pearls for NEET-PG:** * **Breastfeeding:** It is **not contraindicated**. The mother should continue breastfeeding while wearing a mask and practicing cough hygiene. * **Congenital TB:** The most common site of the primary complex in congenital TB is the **Liver** (due to umbilical vein spread), whereas in post-natal TB, it is the **Lungs**. * **Separation:** The infant should **not** be separated from the mother unless she is too ill to care for the child or has MDR-TB. * **Pyridoxine:** Should be supplemented (1 mg/kg) along with INH to prevent peripheral neuropathy.

Question 1

What is the percentage of coincidence between a sore throat and acute rheumatic fever?

Accepted Answer

3%

Answer

5%

Answer

7%

Answer

9%

Question 2

What is the standard treatment for Chlamydia pneumoniae infection?

Accepted Answer

Erythromycin

Answer

Ceftriaxone

Answer

Penicillin

Answer

Sulphonamide

Question 3

A 5-year-old child developed seizures a few months ago. The seizures start with a strange smell (burning rubber), continue with generalized contractions, and end with rhythmic spasms. Consciousness is lost during attacks, and the child is confused afterwards. The child was prescribed phenytoin as the initial treatment. Currently, the parents bring the child for scheduled DTP immunization (diphtheria, tetanus, pertussis). Which of the following is the most appropriate next step in management?

Accepted Answer

Deferral of DTP immunization.

Answer

Immunization with DTP vaccine.

Answer

Change medication to phenobarbital and DTP immunization.

Answer

Two weeks drug holiday and DTP immunization afterwards.

Question 4

Which is the most common organism causing congenital pneumonia?

Accepted Answer

Group B Streptococcus

Answer

Escherichia coli

Answer

Staphylococcus aureus

Answer

Salmonella spp.

Question 5

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

Accepted Answer

Clutton's joints

Answer

Ramsey's joints

Answer

Charcot's joints

Answer

Mercer's joints

Question 6

Which of the following is true about roseola infantum?

Accepted Answer

Caused by HHV 6 and 7

Answer

Defervescence follows the rash

Answer

Slapped cheek appearance is seen

Answer

Otitis media is a common complication

Question 7

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

Accepted Answer

Anti-TB drugs should be started even if chest X-ray and hemogram are normal.

Answer

Treatment should be started only if chest X-ray and hemogram are suggestive.

Answer

Wait until overt signs of TB appear.

Answer

No treatment is required.

Question 8

What is the treatment of varicella in an immunocompetent host?

Accepted Answer

Prevention of complications

Answer

Acyclovir

Answer

Acyclovir and vaccination

Answer

Immunoglobulin

Question 9

What is the recommended treatment for an infant born to a mother with active tuberculosis?

Accepted Answer

Isoniazid prophylaxis

Answer

No treatment required

Answer

Full treatment with Isoniazid, Rifampicin, and Ethambutol

Answer

Treatment with Isoniazid and Rifampicin

Question 10

A 5-year-old child presents with a febrile illness characterized by cough and a blotchy rash. The child has not received routine pediatric care. On examination, there is lymphadenopathy and an erythematous, maculopapular rash behind the ears and along the hairline, involving the neck and, to a lesser extent, the trunk. Examination of this patient's oropharynx would likely reveal which lesion?

Accepted Answer

Multiple small white spots on the buccal mucosa

Answer

Adherent thin, whitish patch on gingiva

Answer

Cold sores on the lips

Answer

Curdy white material overlying an erythematous base on the oral mucosa

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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