Infectious Diseases Practice Questions

Q: What drug is used for the chemoprophylaxis of leptospirosis?

Doxycycline. **Explanation:** Leptospirosis is a zoonotic infection caused by the spirochete *Leptospira interrogans*. Chemoprophylaxis is indicated for individuals with high-risk exposure, such as rescue workers in flood-prone areas or military personnel in endemic jungles. [1] **Why Doxycycline is correct:** **Doxycycline (200 mg orally once weekly)** is the drug of choice for the chemoprophylaxis of leptospirosis. It has been clinically proven to reduce the incidence of symptomatic disease in individuals exposed to contaminated water or soil. Its long half-life and broad-spectrum activity against spirochetes make it the gold standard for prevention. **Why the other options are incorrect:** * **Ampicillin and Amoxicillin:** While these are effective first-line treatments for **mild, symptomatic** leptospirosis (especially in pregnant women or children where tetracyclines are contraindicated), they are not used for routine weekly prophylaxis. * **Cefotaxime:** This is a third-generation cephalosporin used for the treatment of **severe, hospitalized cases** (Weil’s disease) as an alternative to intravenous Penicillin G. It is never used for prophylaxis due to its parenteral administration and risk of promoting antibiotic resistance. **High-Yield Clinical Pearls for NEET-PG:** * **Treatment of Choice (Mild):** Oral Doxycycline or Azithromycin. * **Treatment of Choice (Severe/Weil’s):** IV Penicillin G (Drug of Choice) or IV Ceftriaxone/Cefotaxime. * **Jarisch-Herxheimer Reaction:** Can occur following the initiation of antibiotic therapy in leptospirosis, similar to syphilis. * **Gold Standard Diagnosis:** Microscopic Agglutination Test (MAT). [1] * **Clinical Triad of Weil’s Disease:** Jaundice, Renal failure (azotemia), and Hemorrhage.

Q: What is the most likely diagnosis in a patient from Mauritania whose foot developed these abnormalities over several years?

Actinomycetoma. ***Actinomycetoma*** - Mauritania is located in the **mycetoma belt** of Africa, making actinomycetoma highly endemic in this region with characteristic **Madura foot** presentation. - The chronic progression over several years with **painless swelling**, **deformity**, and likely **draining sinuses** is pathognomonic for mycetoma. *Kaposi's sarcoma* - Presents as **purple-red nodules** or plaques, typically on skin and mucous membranes, not chronic foot deformity. - Associated with **HIV infection** or **HHV-8** and does not cause the characteristic draining sinuses seen in mycetoma. *Leishmaniasis* - **Cutaneous leishmaniasis** presents as **ulcerative lesions** that heal spontaneously, not chronic progressive foot deformity. - **Visceral leishmaniasis** affects internal organs with fever and hepatosplenomegaly, not localized foot abnormalities. *Malignant melanoma* - Appears as an **asymmetric pigmented lesion** with irregular borders and color variation, not chronic swelling. - Grows rapidly over months rather than the **slow progression over years** typical of mycetoma.

Q: Which of the following is an initial presentation of HIV infection?

Bacterial pneumonia. **Explanation:** The correct answer is **Bacterial pneumonia**. While HIV is famously associated with rare opportunistic infections, **bacterial pneumonia** is actually one of the most common initial clinical presentations of HIV infection [1]. Unlike many AIDS-defining illnesses that require a severely low CD4 count, bacterial pneumonia (most commonly caused by *Streptococcus pneumoniae*) can occur at any stage of the disease, including relatively high CD4 counts (>500 cells/µL) [1]. It often serves as the "sentinel event" that leads to an HIV diagnosis. **Analysis of Incorrect Options:** * **Primary CNS Lymphoma (A):** This is an AIDS-defining malignancy strongly associated with EBV. It typically occurs in the advanced stages of immunosuppression, usually when the CD4 count falls below **50 cells/µL**. * **Kaposi Sarcoma (B):** Caused by HHV-8, this is a common AIDS-defining malignancy [2]. While it can occur at moderate CD4 counts, it is generally considered a manifestation of established AIDS rather than an initial presentation in the general HIV population. * **Extrapulmonary Tuberculosis (D):** While TB is the most common opportunistic infection in HIV patients in India, *pulmonary* TB occurs early, whereas *extrapulmonary* TB (e.g., lymph node, meningeal) typically signifies more advanced immunosuppression (CD4 <200-300 cells/µL) [2]. **High-Yield Pearls for NEET-PG:** * **Most common respiratory infection in HIV:** Bacterial pneumonia (specifically *S. pneumoniae*). * **Most common opportunistic infection (OI) in India:** Tuberculosis [2]. * **Most common fungal OI:** *Pneumocystis jirovecii* (PCP) – typically occurs when CD4 <200 cells/µL [1]. * **Initial presentation:** Recurrent bacterial infections or herpes zoster in a young patient should always prompt an HIV screening test [1].

Q: A lung biopsy of an HIV-positive patient shows intra-nuclear basophilic inclusion bodies with a perinuclear halo. The patient's CD4 count was less than 100 at the time of diagnosis. What is the probable cause?

Cytomegalovirus (CMV). ### Explanation The correct answer is **Cytomegalovirus (CMV)**. **1. Why CMV is correct:** The histopathological description of **"intra-nuclear basophilic inclusion bodies with a perinuclear halo"** is the classic description of **"Owl’s Eye" inclusions**. CMV is a double-stranded DNA virus (HHV-5) that causes systemic infections in immunocompromised patients, particularly those with HIV and a **CD4 count <50–100 cells/mm³** [1]. In the lungs, CMV pneumonitis presents with these characteristic large cells (cytomegaly) containing dark viral inclusions surrounded by a clear halo. **2. Why the other options are incorrect:** * **Mycobacterium avium complex (MAC):** Typically presents with acid-fast bacilli within macrophages. It usually causes systemic symptoms (fever, night sweats) and diarrhea rather than isolated pulmonary pathology in HIV. * **Pneumocystis jirovecii (PJP):** On histology, PJP shows a characteristic **"crushed ping-pong ball"** or "cup-and-saucer" appearance on Silver stain (GMS) [2]. It presents with a "foamy" alveolar exudate, not intranuclear inclusions. * **Tuberculosis (TB):** Characterized by **caseating granulomas** and Acid-Fast Bacilli (AFB) on Ziehl-Neelsen staining [2]. While common in HIV, it does not produce viral inclusion bodies. **3. NEET-PG High-Yield Pearls:** * **CMV Retinitis:** The most common clinical manifestation of CMV in HIV (presents as "pizza-pie" or "cheese and ketchup" fundus). * **CMV Esophagitis:** Characterized by **linear/longitudinal ulcers** (vs. HSV which causes punched-out/volcano ulcers). * **Drug of Choice:** **Ganciclovir** is the first-line treatment; Foscarnet is used for resistant cases. * **Biopsy Gold Standard:** Presence of Owl's eye inclusions is pathognomonic.

Q: A healthcare worker sustains a needle-prick injury from a patient with HIV. What is the immediate management or treatment required?

Antiretroviral therapy. ### Explanation **Correct Answer: B. Antiretroviral therapy** The immediate management of a needle-stick injury (NSI) involving a known HIV-positive source is the initiation of **Post-Exposure Prophylaxis (PEP)** using Antiretroviral Therapy (ART). The goal is to inhibit viral replication before the virus can establish a systemic infection. According to NACO guidelines, PEP should be started as soon as possible—ideally within **2 hours** and no later than **72 hours**—and continued for **28 days**. **Analysis of Incorrect Options:** * **A & C (Vaccination):** There is currently no effective prophylactic vaccine available for HIV. Vaccination is a standard protocol for Hepatitis B post-exposure, but not for HIV. * **D (HIV testing):** While baseline testing of the healthcare worker (HCW) is mandatory to establish their pre-exposure status, it is a diagnostic step, not a "treatment" or "management" to prevent infection. Treatment (ART) must not be delayed while waiting for test results. **High-Yield Clinical Pearls for NEET-PG:** * **The "Golden Period":** PEP is most effective if started within 2 hours of exposure. * **Standard PEP Regimen (NACO):** A 3-drug regimen is now preferred: **Tenofovir (300mg) + Lamivudine (300mg) + Dolutegravir (50mg)** once daily for 28 days. * **Immediate First Aid:** Wash the site with soap and water. **Do not scrub** or use antiseptics like bleach; **do not squeeze** the wound to induce bleeding. * **Risk of Transmission:** The average risk of HIV transmission after a percutaneous exposure to HIV-infected blood is approximately **0.3%**. (Compare this to Hepatitis B, which is 6–30%, and Hepatitis C, which is ~1.8%).

Q: A 65-year-old man presents with fever, severe headache, and nuchal rigidity. Physical examination shows a Glasgow coma score of 7. Lumbar puncture reveals cloudy cerebrospinal fluid (CSF) with 1200 neutrophils/mm3, elevated protein, and decreased glucose. Which of the following is the most probable etiologic agent of this condition?

Streptococcus pneumoniae. **Explanation:** The clinical presentation of fever, headache, and nuchal rigidity (meningismus) combined with a GCS of 7 indicates **Acute Bacterial Meningitis**. [1] **1. Why Streptococcus pneumoniae is correct:** The CSF analysis is the diagnostic gold standard. A "cloudy" appearance with a high neutrophil count (>1000/mm³), elevated protein, and low glucose is classic for bacterial etiology. In adults over 20 years of age, **Streptococcus pneumoniae** is the most common cause of community-acquired bacterial meningitis. The severe presentation (GCS 7) is also characteristic, as pneumococcal meningitis often carries a higher morbidity and mortality rate compared to other pathogens. [1] **2. Why the other options are incorrect:** * **Arbovirus & Herpesvirus:** These cause viral meningitis/encephalitis. CSF typically shows **lymphocytic pleocytosis**, normal glucose levels, and clear fluid. [1] While HSV-1 can cause severe encephalitis, the CSF profile here (1200 neutrophils, low glucose) is purely bacterial. * **Mycobacterium tuberculosis:** Tuberculous meningitis usually presents subacutely. [2] CSF analysis typically shows a **lymphocytic predominance** (not neutrophils) and a characteristically very high protein level with moderately low glucose. [2] **3. NEET-PG High-Yield Pearls:** * **Most common cause overall (Adults):** *S. pneumoniae*. * **Most common cause (Adolescents/Young Adults):** *Neisseria meningitidis* (look for petechial rashes). * **Empiric Treatment:** Ceftriaxone + Vancomycin. Add **Ampicillin** if *Listeria* is suspected (elderly or immunocompromised). [1] * **Steroids:** Dexamethasone should be given **before or with** the first dose of antibiotics to reduce neurological complications (especially in pneumococcal meningitis). * **CSF Glucose:** A CSF-to-serum glucose ratio of **<0.4** is highly suggestive of bacterial meningitis.

Q: What is the most common late central nervous system complication of HIV infection?

Dementia. **Explanation:** **HIV-Associated Dementia (HAD)**, also known as AIDS Dementia Complex, is the most common late-stage CNS complication of HIV infection [3]. It typically occurs when CD4 counts drop below **200 cells/mm³**. The underlying pathophysiology involves the direct infection of brain macrophages and microglia by HIV, leading to a chronic inflammatory state and neuronal damage, primarily affecting the subcortical structures. Clinically, it presents as a triad of cognitive decline, behavioral changes, and motor dysfunction. **Analysis of Options:** * **A. Dementia (Correct):** It is the hallmark late neurocognitive complication [1]. With the advent of HAART, the incidence has decreased, but it remains the most frequent primary CNS manifestation in advanced AIDS. * **B. Ataxia:** While ataxia can occur as part of the motor symptoms of HAD or due to opportunistic infections like Progressive Multifocal Leukoencephalopathy (PML), it is a focal sign rather than the most common overall complication. * **C. Seizures:** These are usually secondary to space-occupying lesions (e.g., CNS Toxoplasmosis or Primary CNS Lymphoma) [2] rather than a primary effect of the virus itself. * **D. Delirium:** This is an acute, reversible state of confusion often caused by systemic infections, metabolic derangements, or drug side effects, rather than a chronic late-stage complication of the virus. **Clinical Pearls for NEET-PG:** * **Most common opportunistic infection of CNS in HIV:** Toxoplasmosis [2]. * **Most common fungal infection of CNS in HIV:** Cryptococcal Meningitis. * **Most common cause of a space-occupying lesion in HIV:** Toxoplasmosis (Ring-enhancing lesions) [2]. * **Key distinction:** HAD is a **subcortical dementia** (characterized by psychomotor slowing), unlike Alzheimer’s, which is a cortical dementia.

Q: What is the next step in the management of a patient with a positive sputum smear for tuberculosis but a negative chest X-ray?

Start anti-tuberculosis treatment (ATT). **Explanation:** The diagnosis of Pulmonary Tuberculosis (PTB) in the National Tuberculosis Elimination Programme (NTEP) is primarily microbiological. A positive sputum smear indicates the presence of acid-fast bacilli (AFB), which is sufficient evidence of active disease, regardless of radiological findings. **1. Why Option B is Correct:** In clinical practice, a positive sputum smear has high specificity. A negative chest X-ray (CXR) does not rule out TB, as early-stage disease or endobronchial TB may not show visible parenchymal shadows. According to NTEP guidelines, any "Microbiologically Confirmed" case must be initiated on **Anti-Tuberculosis Treatment (ATT)** immediately to interrupt the chain of transmission and prevent clinical deterioration. **2. Why Other Options are Incorrect:** * **Option A & D:** Repeating tests (CXR or Smear) leads to unnecessary "diagnostic delay." A single positive smear is diagnostic in a symptomatic patient. * **Option C:** While CBNAAT (GeneXpert) is the preferred initial diagnostic tool under NTEP for its high sensitivity and ability to detect Rifampicin resistance, the question states the patient is *already* smear-positive. Treatment should not be withheld while waiting for further tests unless drug resistance is specifically suspected. **Clinical Pearls for NEET-PG:** * **Microbiologically Confirmed TB:** Defined as a patient with a biological specimen positive for AFB by smear microscopy, or positive for *M. tuberculosis* by NAAT (like CBNAAT/Truenat) or culture. * **Radiology vs. Microbiology:** Microbiology is the "Gold Standard." A positive smear always supersedes a negative X-ray. * **Infectivity:** Smear-positive patients are the most infectious; prompt ATT is the most effective public health intervention to reduce the "Annual Risk of Tuberculosis Infection" (ARTI).

Question 1

A 20-year-old male goes swimming and after a few days develops diffuse itching with rashes over his body. Several weeks later, he develops lancinating pain down his legs and in all his toes. Within a few days, he develops paraparesis and problems with bowel and bladder control, resulting in urinary retention. What is your initial diagnostic approach for this patient?

Accepted Answer

Order an MRI scan

Answer

Initiate anticoagulation

Answer

Perform spinal angiography

Answer

Perform sensory evoked potential testing

Question 2

What drug is used for the chemoprophylaxis of leptospirosis?

Accepted Answer

Doxycycline

Answer

Ampicillin

Answer

Amoxicillin

Answer

Cefotaxime

Question 3

What is the most likely diagnosis in a patient from Mauritania whose foot developed these abnormalities over several years?

Accepted Answer

Actinomycetoma

Answer

Kaposi's sarcoma

Answer

Leishmaniasis

Answer

Malignant melanoma

Question 4

Which of the following is an initial presentation of HIV infection?

Accepted Answer

Bacterial pneumonia

Answer

Primary CNS lymphoma

Answer

Kaposi sarcoma

Answer

Extrapulmonary tuberculosis

Question 5

A lung biopsy of an HIV-positive patient shows intra-nuclear basophilic inclusion bodies with a perinuclear halo. The patient's CD4 count was less than 100 at the time of diagnosis. What is the probable cause?

Accepted Answer

Cytomegalovirus (CMV)

Answer

Mycobacterium avium complex (MAC)

Answer

Pneumocystis jirovecii pneumonia (PJP)

Answer

Tuberculosis (TB)

Question 6

A healthcare worker sustains a needle-prick injury from a patient with HIV. What is the immediate management or treatment required?

Accepted Answer

Antiretroviral therapy

Answer

Prophylactic vaccination

Answer

Vaccination and antiretroviral therapy

Answer

HIV testing

Question 7

A 65-year-old man presents with fever, severe headache, and nuchal rigidity. Physical examination shows a Glasgow coma score of 7. Lumbar puncture reveals cloudy cerebrospinal fluid (CSF) with 1200 neutrophils/mm3, elevated protein, and decreased glucose. Which of the following is the most probable etiologic agent of this condition?

Accepted Answer

Streptococcus pneumoniae

Answer

Arbovirus

Answer

Herpesvirus

Answer

Mycobacterium tuberculosis

Question 8

What is the most common late central nervous system complication of HIV infection?

Accepted Answer

Dementia

Answer

Ataxia

Answer

Seizures

Answer

Delirium

Question 9

A 23-year-old patient, studying abroad, visited his hometown and developed a high-grade fever (103°F) after 3 days. He took acetaminophen and subsequently complained of myalgias, cough, and mild shortness of breath. A nasopharyngeal swab tested positive for COVID-19. Which of the following statements regarding the patient's next steps in management is false?

Accepted Answer

HCQ + Azithromycin

Answer

Start Doxycycline 100mg

Answer

Start Ivermectin 12mg

Answer

Dexamethasone is used

Question 10

What is the next step in the management of a patient with a positive sputum smear for tuberculosis but a negative chest X-ray?

Accepted Answer

Start anti-tuberculosis treatment (ATT)

Answer

Repeat chest X-ray

Answer

Perform CBNAAT

Answer

Repeat sputum smear

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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