Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 661: Scrofula is a tuberculosis of which of the following structures?

A. Skin
B. Lymph node (Correct Answer)
C. Spine
D. Lungs

Explanation: **Explanation:** **Scrofula** (also known as Tuberculous Cervical Adenitis) is the most common manifestation of extrapulmonary tuberculosis. It refers specifically to a **tuberculous infection of the lymph nodes**, most commonly involving the cervical chain [1]. 1. **Why Lymph Node is Correct:** In adults, scrofula is primarily caused by *Mycobacterium tuberculosis*, while in children, it is often caused by non-tuberculous mycobacteria (NTM) like *M. avium-intracellulare*. The infection typically presents as a painless, "cold" swelling in the neck [1]. If left untreated, these nodes can undergo caseous necrosis, leading to the formation of a **sinus tract** that drains through the skin [1]. 2. **Why Other Options are Incorrect:** * **Skin:** While scrofula can involve the skin via a draining sinus, primary TB of the skin is known as *Lupus vulgaris* or *Tuberculosis verrucosa cutis*. * **Spine:** Tuberculosis of the spine is known as **Pott’s Disease**, characterized by vertebral destruction and kyphotic deformity [2]. * **Lungs:** This is primary pulmonary tuberculosis, the most common site of TB infection overall, but it is not termed scrofula [3]. **High-Yield Clinical Pearls for NEET-PG:** * **Cold Abscess:** Scrofula is termed a "cold abscess" because it lacks the typical signs of acute inflammation (redness, heat, and pain) seen in pyogenic infections. * **Diagnosis:** Fine Needle Aspiration Cytology (FNAC) is the initial investigation of choice, showing granulomatous inflammation and caseation. * **Most Common Site:** The **jugulodigastric** lymph node is the most frequently involved node in the cervical chain. * **Treatment:** Standard Antitubercular Therapy (ATT) for 6 months is the mainstay of management.

Question 662: A laboratory technician was accidentally exposed to an HIV-seropositive serum sample. What is the role of zidovudine in the post-exposure prophylaxis for this patient?

A. To prevent acquisition of HIV infection. (Correct Answer)
B. To make the patient seronegative.
C. To delay the progression of the disease.
D. None of the above.

Explanation: ### Explanation **Correct Option: A (To prevent acquisition of HIV infection)** The primary goal of Post-Exposure Prophylaxis (PEP) is to prevent the establishment of a systemic viral infection following accidental exposure [1]. When a person is exposed to HIV, the virus takes time to disseminate from the site of entry to the regional lymph nodes and eventually the bloodstream [2]. Administering antiretroviral drugs like **Zidovudine** (an NRTI) inhibits viral replication during this critical "window period," effectively preventing the virus from integrating into the host genome and establishing a permanent infection. **Analysis of Incorrect Options:** * **Option B:** Seronegativity refers to the absence of antibodies. While PEP prevents infection (and thus prevents the patient from ever becoming seropositive), the *purpose* of the drug is to stop the virus, not to manipulate antibody test results. * **Option C:** Delaying disease progression is the goal of Highly Active Antiretroviral Therapy (HAART) in patients who are **already** HIV-positive. In the context of PEP, the aim is "prevention," not "management" of a chronic state. **NEET-PG High-Yield Pearls:** 1. **Timing:** PEP should be started as soon as possible, ideally within **2 hours**, and no later than **72 hours** post-exposure [1]. 2. **Duration:** The standard duration for PEP is **28 days**. 3. **Current Regimen:** While Zidovudine was historically the mainstay, current NACO/WHO guidelines prefer a three-drug regimen (e.g., **Tenofovir + Lamivudine + Dolutegravir**). 4. **Risk of Transmission:** The average risk of HIV transmission after a percutaneous needle-stick injury is approximately **0.3%** [2].

Question 663: What is the most common cause of meningitis in adults?

A. Haemophilus influenzae
B. Neisseria meningitidis
C. Staphylococcus aureus
D. Streptococcus pneumoniae (Correct Answer)

Explanation: **Explanation:** **Streptococcus pneumoniae (Pneumococcus)** is currently the most common cause of community-acquired bacterial meningitis in adults worldwide, accounting for approximately 50% of all cases. This shift occurred primarily due to the widespread implementation of the *Haemophilus influenzae* type b (Hib) vaccine. Pneumococcal meningitis is often associated with concurrent infections like pneumonia, otitis media, or sinusitis and carries the highest mortality rate among bacterial causes [1]. **Analysis of Incorrect Options:** * **A. Haemophilus influenzae:** Historically the leading cause in children, its incidence has plummeted due to universal Hib vaccination. It is now a rare cause in adults unless there is a history of neurosurgery or head trauma. * **B. Neisseria meningitidis:** This is the most common cause in children and young adults (especially in outbreaks or crowded settings like dormitories). While significant, it ranks second to *S. pneumoniae* in the general adult population. * **C. Staphylococcus aureus:** This is an uncommon cause of community-acquired meningitis. It is typically seen in post-neurosurgical patients, those with CSF shunts, or secondary to infective endocarditis. **High-Yield Clinical Pearls for NEET-PG:** * **Most common cause overall (Adults):** *Streptococcus pneumoniae*. * **Most common cause in Neonates (<1 month):** Group B Streptococcus (*S. agalactiae*), followed by *E. coli* and *Listeria*. * **Empiric Treatment:** Vancomycin + 3rd Generation Cephalosporin (Ceftriaxone/Cefotaxime) [1]. Add Ampicillin if *Listeria* is suspected (elderly/immunocompromised). * **Dexamethasone:** Should be administered before or with the first dose of antibiotics to reduce neurological sequelae (especially in Pneumococcal meningitis).

Question 664: All are viral causes of prolonged fever of unknown origin (PUO) except?

A. EBV (Epstein-Barr virus)
B. CMV (Cytomegalovirus)
C. HIV (Human Immunodeficiency Virus)
D. Leptospirosis (Correct Answer)

Explanation: The diagnosis of **Fever of Unknown Origin (FUO)** typically requires a fever >38.3°C (101°F) on several occasions, lasting for at least 3 weeks, with no diagnosis reached after one week of inpatient investigation (or three outpatient visits). **Why Leptospirosis is the Correct Answer:** Leptospirosis is caused by the spirochete *Leptospira interrogans* [4]. It is a **bacterial**, not a viral, infection [5]. Clinically, it usually presents as an acute febrile illness (biphasic) rather than a prolonged FUO [5]. While it can cause severe systemic disease (Weil’s syndrome), its etiology is fundamentally different from the viral options listed. **Analysis of Incorrect Options:** * **EBV (Epstein-Barr Virus):** A classic cause of infectious mononucleosis. In adults, it can present with prolonged fever, lymphadenopathy, and splenomegaly, often meeting FUO criteria [1]. * **CMV (Cytomegalovirus):** CMV mononucleosis is a leading viral cause of FUO in immunocompetent adults, often presenting as "typhoidal" (fever without prominent lymphadenopathy or pharyngitis) and can last 2 weeks or more [2]. * **HIV (Human Immunodeficiency Virus):** Acute HIV infection (Seroconversion illness) or opportunistic infections in advanced stages are major contributors to the "HIV-associated FUO" category [3]. **High-Yield Clinical Pearls for NEET-PG:** * **Most common cause of FUO:** Infections (TB is the #1 cause in India), followed by Malignancies and Connective Tissue Disorders. * **Viral FUO:** EBV and CMV are the most frequent viral triggers in non-immunocompromised patients. * **Leptospirosis Hallmark:** Conjunctival suffusion (redness without exudate) and calf tenderness are classic diagnostic clues [5]. * **Drug Fever:** Always consider this if the patient is on medications like sulfonamides, penicillins, or phenytoin.

Question 665: What is the most common disease caused by CMV in post-renal transplant patients?

A. Pyelonephritis
B. Meningitis
C. Pneumonia (Correct Answer)
D. Gastrointestinal ulceration

Explanation: **Explanation:** Cytomegalovirus (CMV) is the most significant viral pathogen in the post-transplant period, typically manifesting between 1 to 6 months after transplantation [1]. In the context of **renal transplant recipients**, while CMV can affect multiple organ systems, **Pneumonia (Interstitial Pneumonitis)** is considered the most common and serious tissue-invasive manifestation. It presents with fever, dry cough, and dyspnea, often showing bilateral interstitial infiltrates on chest X-ray. **Analysis of Options:** * **Option A (Pyelonephritis):** This is usually caused by bacterial pathogens (like *E. coli*) or Polyomavirus (BK virus) which causes nephropathy, but it is not a classic manifestation of CMV. * **Option B (Meningitis):** CMV rarely involves the CNS in transplant patients. CNS involvement is more common in HIV patients (as encephalitis) rather than transplant recipients. * **Option D (Gastrointestinal ulceration):** While CMV is a common cause of GI ulcers and colitis in immunocompromised states, in the specific hierarchy of post-renal transplant complications, pulmonary involvement (Pneumonia) takes precedence as the most common invasive disease. **High-Yield Pearls for NEET-PG:** * **Risk Factor:** The highest risk for CMV disease is in **Seronegative recipients receiving an organ from a Seropositive donor (D+/R-)** [2]. * **Diagnosis:** **pp65 antigenemia** assay or **Quantitative PCR** for CMV DNA are the preferred diagnostic methods [1]. * **Histology:** Look for **"Owl’s Eye" appearance** (large intranuclear inclusion bodies with a clear halo). * **Treatment:** **Valganciclovir** is used for prophylaxis, while **IV Ganciclovir** is the drug of choice for established CMV disease [2]. Foscarnet is used in ganciclovir-resistant cases.

Question 666: Which cranial nerve is commonly involved in meningeal tuberculosis infection?

A. 7th nerve
B. 8th nerve
C. Ocular nerve (Correct Answer)
D. Oculomotor nerve

Explanation: Tuberculous Meningitis (TBM) is characterized by a thick, gelatinous inflammatory exudate that predominantly accumulates at the **base of the brain** (basal cisterns). This predilection for the skull base leads to the entrapment and compression of various cranial nerves as they exit the brainstem [1]. **Why the Correct Answer is Right:** The term **"Ocular nerves"** (collectively referring to the nerves controlling eye movements: III, IV, and VI) represents the most common group of cranial nerves involved in TBM [2]. Among these, the **6th cranial nerve (Abducens)** is the most frequently affected individual nerve. This occurs due to its long intracranial course and its vulnerability to increased intracranial pressure (ICP) and basal exudates. Involvement of these nerves leads to clinical features like diplopia and ophthalmoplegia [2]. **Analysis of Incorrect Options:** * **7th Nerve (Facial):** While the facial nerve can be involved in TBM, it is less common than the ocular nerves. It is more typically associated with conditions like Bell’s palsy or Ramsay Hunt syndrome. * **8th Nerve (Vestibulocochlear):** Hearing loss can occur in TBM, often as a complication of streptomycin treatment or direct basal inflammation, but it is not the most common finding [1]. * **Oculomotor Nerve (3rd Nerve):** While the 3rd nerve is frequently involved, the broader category of "Ocular nerves" (which includes the 6th nerve, the single most common) is the preferred answer in this context. **High-Yield Clinical Pearls for NEET-PG:** * **Most common cranial nerve involved in TBM:** 6th Nerve (Abducens). * **Pathognomonic finding on Imaging:** Contrast enhancement of the basal cisterns (Basal Arachnoiditis) and hydrocephalus [1]. * **CSF Findings in TBM:** High protein, low glucose, and **lymphocytic pleocytosis** [1]. * **Complication:** Arteritis of the Circle of Willis leading to "Border zone" infarcts (most commonly in the territory of the Middle Cerebral Artery) [1].

Question 667: Herpes simplex infection can lead to which of the following?

A. Frontal lobe infarction
B. Parietal lobe infarction
C. Temporal lobe involvement (Correct Answer)
D. Occipital neuralgia

Explanation: Explanation: **Correct Answer: C. Temporal lobe involvement** Herpes Simplex Virus (HSV-1) is the most common cause of sporadic fatal encephalitis worldwide. The hallmark of **Herpes Simplex Encephalitis (HSE)** is its striking predilection for the **limbic system**, specifically the **medial temporal lobes** [1] and the inferior frontal lobes. The virus typically reaches the brain via retrograde axonal transport along the olfactory or trigeminal nerves. Pathologically, it causes acute necrotizing hemorrhage and edema in these regions [1]. Clinically, this manifests as sudden onset fever, headache, seizures, and characteristic behavioral changes or aphasia. **Why other options are incorrect:** * **A & B (Frontal/Parietal lobe infarction):** While HSE can cause localized edema and necrosis, it is not primarily a vascular/ischemic event (infarction). Furthermore, while the inferior frontal lobe can be involved, the **temporal lobe** is the classic, most high-yield site of involvement. * **D (Occipital neuralgia):** This is a paroxysmal pain condition involving the greater or lesser occipital nerves. While HSV can remain latent in sensory ganglia (like the trigeminal ganglion) [2], it is not a recognized cause of occipital neuralgia. **High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard Diagnosis:** CSF PCR for HSV DNA (highly sensitive and specific). * **EEG Findings:** Periodic Lateralizing Epileptiform Discharges (**PLEDs**) over the temporal lobes are characteristic. * **Imaging:** MRI is the investigation of choice; it shows T2/FLAIR hyperintensity in the medial temporal lobes. * **Treatment:** Immediate IV **Acyclovir** (10 mg/kg every 8 hours) should be started empirically if HSE is suspected, as delay increases mortality.

Question 668: A 6-week pregnant lady is diagnosed with sputum-positive tuberculosis. What is the best management?

A. Wait for the second trimester to start anti-tuberculosis treatment (ATT).
B. Start Category I ATT in the first trimester. (Correct Answer)
C. Start Category II ATT in the first trimester.
D. Start Category III ATT in the second trimester.

Explanation: ### Explanation **1. Why Option B is Correct:** The management of Tuberculosis (TB) in pregnancy follows the principle that the risk of untreated TB to the mother and fetus far outweighs the risk of the drugs used for treatment. According to **RNTCP (NTEP) and WHO guidelines**, a pregnant woman diagnosed with TB should start **Category I ATT (2HREZ + 4HRE)** immediately, regardless of the gestational age [1]. Most first-line drugs (Isoniazid, Rifampicin, Ethambutol, and Pyrazinamide) are considered safe in the first trimester and are not associated with increased teratogenic risks. **2. Why Other Options are Incorrect:** * **Option A:** Delaying treatment until the second trimester increases the risk of maternal morbidity, spontaneous abortion, and congenital TB. Treatment should never be deferred. * **Option C:** Category II (which included Streptomycin) is no longer the standard of care under current NTEP guidelines. Furthermore, **Streptomycin is contraindicated** in pregnancy as it is ototoxic to the fetus (causes 8th cranial nerve damage). * **Option D:** Category III is an obsolete classification. All new cases are treated with the standard 6-month regimen (Category I). **3. High-Yield Clinical Pearls for NEET-PG:** * **Drug Safety:** H, R, E, and Z are safe. **Streptomycin** is the only first-line drug that is strictly **contraindicated**. * **Pyridoxine (Vitamin B6) Supplementation:** Mandatory (10–25 mg/day) for all pregnant women on ATT to prevent Isoniazid-induced peripheral neuropathy in the mother and seizures in the newborn [1]. * **Breastfeeding:** ATT is not contraindicated during breastfeeding. The concentration of drugs in breast milk is too low to protect the baby or cause toxicity. * **Congenital TB:** The most common site of primary complex in congenital TB is the **Liver** (via the umbilical vein).

Question 669: Which of the following clinical features is NOT typically seen in leptospirosis?

A. Jaundice, which may be intense
B. Hemorrhage
C. Hepatomegaly
D. Massive splenomegaly (Correct Answer)

Explanation: Leptospirosis is a zoonotic infection caused by the spirochete Leptospira interrogans [1]. The severe form of the disease, known as Weil’s Disease, is characterized by the triad of jaundice, renal failure, and hemorrhage [1]. **Why "Massive Splenomegaly" is the correct answer:** While mild splenomegaly can occur in about 15–25% of cases, **massive splenomegaly** is not a feature of leptospirosis. In the context of infectious diseases in India, massive splenomegaly should instead point toward diagnoses like Chronic Malaria, Visceral Leishmaniasis (Kala-azar), or Schistosomiasis [2]. **Analysis of incorrect options:** * **Jaundice (Option A):** This is a hallmark of severe leptospirosis [1]. Unlike viral hepatitis, the jaundice in leptospirosis is often "orange-yellow" and occurs despite relatively mild elevations in liver enzymes (AST/ALT rarely exceed 500 U/L). * **Hemorrhage (Option B):** Capillary fragility and thrombocytopenia lead to bleeding manifestations, ranging from epistaxis and petechiae to life-threatening pulmonary hemorrhage (a leading cause of death) [1]. * **Hepatomegaly (Option C):** Enlargement of the liver is common in the icteric phase [1]. The liver is often tender, though true hepatic failure is rare as the jaundice is primarily due to hepatocellular dysfunction and canalicular cholestasis rather than necrosis. **NEET-PG High-Yield Pearls:** * **Conjunctival Suffusion:** The most characteristic clinical sign (redness without inflammatory exudate). * **Biphasic Pattern:** Leptospiremic phase (fever, myalgia) followed by the Immune phase (meningitis, uveitis, renal failure) [1]. * **Lab Clue:** Disproportionately high Bilirubin with mildly raised Transaminases and elevated Creatine Phosphokinase (CPK) due to myositis. * **Treatment:** Doxycycline (prophylaxis/mild disease) or IV Penicillin G (severe disease).

Question 670: In which of the following conditions are steroids useful in treating a tuberculosis patient?

A. Endobronchial tuberculosis
B. Tuberculous osteomyelitis
C. Lymphadenitis (Correct Answer)
D. Pneumonia

Explanation: **Explanation:** The use of corticosteroids in tuberculosis (TB) is primarily indicated to suppress the host's exaggerated inflammatory response, which can lead to tissue damage or obstructive complications. **Why Lymphadenitis is correct:** In **Tuberculous Lymphadenitis**, steroids are indicated specifically when there is a **paradoxical worsening** (Immune Reconstitution Inflammatory Syndrome - IRIS) or when massive lymphadenopathy causes pressure symptoms on adjacent structures (e.g., airway or major vessels) [3]. Steroids help reduce the size of the nodes and prevent sinus formation or suppuration by modulating the delayed-type hypersensitivity reaction. **Analysis of Incorrect Options:** * **Endobronchial TB:** While steroids were historically used to prevent bronchial stenosis, current evidence suggests they do not significantly alter the long-term outcome of airway narrowing compared to antitubercular therapy (ATT) alone. * **Tuberculous Osteomyelitis:** Treatment is strictly pharmacological (ATT) and sometimes surgical [1], [2]. Steroids have no proven role and may interfere with bone healing or mask secondary infections. * **Pneumonia:** Standard TB pneumonia is managed with ATT. Steroids are only considered in cases of severe respiratory failure/ARDS or miliary TB with hypoxia, but not as a routine treatment for localized pneumonia. **NEET-PG High-Yield Pearls:** Absolute indications for steroids in TB (The "Must-Know" List): 1. **TB Meningitis:** Reduces mortality and neurological sequelae (Stage II and III) [1]. 2. **TB Pericarditis:** Prevents constrictive pericarditis and reduces the need for pericardiectomy [1]. 3. **Adrenal TB (Addison’s Disease):** Replacement therapy for adrenal insufficiency. 4. **Miliary TB:** If there is associated hypoxia or ARDS. 5. **Genitourinary TB:** To prevent ureteral strictures.

Practice by Chapter

Principles of Antimicrobial Therapy

Practice Questions

Fever of Unknown Origin

Practice Questions

HIV/AIDS and Related Infections

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Tuberculosis and Mycobacterial Diseases

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Tropical and Parasitic Infections

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Viral Infections (Hepatitis, Herpes, etc.)

Practice Questions

Healthcare-Associated Infections

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Fungal Infections

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Sepsis and Septic Shock

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Infection in Immunocompromised Hosts

Practice Questions

Emerging and Re-emerging Infections

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Antimicrobial Resistance

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Vaccination Principles

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