Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 1351: The most common cause of lung abscess is:

A. Lymphatic spread
B. Aspiration (Correct Answer)
C. Hematogenous spread from distant site
D. Direct contact

Explanation: **Aspiration** - **Aspiration of oropharyngeal secretions** containing anaerobic bacteria is the most common mechanism leading to lung abscess formation. [1] - This often occurs in individuals with **impaired consciousness** (e.g., due to alcohol intoxication, stroke, seizures), dysphagia, or poor dental hygiene. [1] *Hematogenous spread from distant site* - While possible, **hematogenous spread** (e.g., from endocarditis or septic thrombophlebitis) is a less common cause of lung abscess compared to aspiration. - This typically results in **multiple, diffuse abscesses**, rather than a single, large one. *Direct contact* - **Direct contact** or extension from an adjacent infection (e.g., empyema) can cause lung involvement, but it is not the most frequent etiology of primary lung abscess. - This refers to the spread from a contiguous thoracic infection invading the lung parenchyma. *Lymphatic spread* - **Lymphatic spread** is a rare cause of lung abscess and is more typically associated with the dissemination of malignancy or certain fungal infections rather than bacterial abscess formation. - The lymphatic system primarily drains fluid and immune cells, not typically leading to focal pus collections.

Question 1352: Amoebic liver abscess most commonly affects which part of the liver?

A. Right lobe of liver (Correct Answer)
B. Left lobe of liver
C. Portal vein
D. Right pleural cavity

Explanation: ***Right lobe of liver*** - The **right lobe** of the liver [1] is supplied by a larger proportion of blood from the superior mesenteric and splenic veins, making it more susceptible to parasitic emboli from the bowel. - Due to its larger size and more direct blood supply from the **portal vein**, the right lobe is the most common site (approximately 80-90%) for amoebic liver abscess formation [1]. *Left lobe of liver* - While it can be affected, the **left lobe** is less commonly involved in amoebic liver abscesses compared to the right lobe. - Its blood supply directly from the **portal vein** is less direct and abundant for parasitic entry than that of the right lobe. *Portal vein* - The **portal vein** is the route of entry for *Entamoeba histolytica* cysts from the intestines to the liver, but it is not the site where an abscess forms. - Abscesses form in the **liver parenchyma** [1] after the trophozoites travel via the portal venules and elicit an inflammatory response. *Right pleural cavity* - The **right pleural cavity** is a potential site for complications of a ruptured amoebic liver abscess, leading to **pleural effusion** or **empyema**. - However, it is not the primary site where the amoebic liver abscess itself develops, as it is outside the liver.

Question 1353: Leprosy affects all the following except:

A. Eyes
B. Nerves
C. Ovaries (Correct Answer)
D. Testes

Explanation: ***Ovaries*** - The **ovaries** are generally spared in leprosy due to their internal location and higher temperature, which is not conducive to the growth of *Mycobacterium leprae*. - *M. leprae* prefers cooler body temperatures (around 27-33°C), leading to its predilection for superficial tissues. *Testes* - The **testes** are frequently affected in leprosy, particularly in lepromatous forms, due to their cooler temperature. - Involvement can lead to **orchitis**, **atrophy**, and **infertility** in males [1]. *Eyes* - The **eyes** are commonly affected in leprosy, especially the anterior segment (cornea, iris, ciliary body) [1]. - Complications can include **keratitis**, **iritis**, glaucoma, and vision loss due to nerve damage and direct *M. leprae* invasion [1]. *Nerves* - **Nerves**, particularly peripheral nerves, are a hallmark of leprosy, as *M. leprae* has a strong tropism for Schwann cells [1]. - This leads to **nerve thickening**, loss of sensation, and motor weakness, which are crucial diagnostic features [1].

Question 1354: Which infection is not common in HIV patients?

A. Atypical mycobacterial infection
B. Candidiasis
C. Cryptosporidiosis
D. Aspergillosis (Correct Answer)

Explanation: ***Aspergillosis*** - While *Aspergillus* can cause infection in severely immunocompromised individuals, it is **less common** in HIV patients compared to other opportunistic infections listed, especially in the era of effective antiretroviral therapy (ART). - Its prevalence in HIV patients is significantly lower than in other populations, such as those with **neutropenia** or following **organ transplantation**. *Cryptosporidiosis* - This is a well-known **opportunistic infection** in HIV patients, especially those with low CD4 counts, causing **severe, chronic diarrhea** [1]. - It often leads to significant **malabsorption** and weight loss, representing a characteristic manifestation of advanced HIV disease [1]. *Atypical mycobacterial infection* - Infections by **Mycobacterium avium complex (MAC)** are very common in HIV patients with advanced immunosuppression (CD4 count <50 cells/µL) [1]. - MAC can cause **disseminated disease**, including fever, night sweats, weight loss, and anemia [1]. *Candidiasis* - **Oropharyngeal** and **esophageal candidiasis** are extremely common in HIV patients, often indicating immune suppression [1]. - While generally not life-threatening, it can be a significant cause of **discomfort** and difficulty eating for individuals with HIV [1].

Question 1355: ASLO titres are primarily associated with which condition?

A. Acute rheumatoid arthritis
B. Acute rheumatic fever (Correct Answer)
C. Ankylosing spondylitis
D. Osteoarthritis

Explanation: ***Acute rheumatic fever*** - **Antistreptolysin O (ASLO)** titres are antibodies produced in response to a pharyngeal infection by **Streptococcus pyogenes (Group A Streptococcus)**, which is the causative agent of acute rheumatic fever [1]. - Elevated ASLO titres indicate a recent streptococcal infection, which is crucial for the diagnosis of **acute rheumatic fever**, especially in the absence of a clear history of infection [1]. *Acute rheumatoid arthritis* - **Rheumatoid arthritis** is an autoimmune disease primarily diagnosed by clinical symptoms, imaging, and other serological markers like **rheumatoid factor (RF)** and **anti-cyclic citrullinated peptide (anti-CCP) antibodies** [2]. - ASLO titres are not a diagnostic marker for rheumatoid arthritis and would typically be negative unless there is a co-occurring streptococcal infection. *Ankylosing spondylitis* - **Ankylosing spondylitis** is a chronic inflammatory disease primarily affecting the spine and sacroiliac joints, strongly associated with the **HLA-B27** gene [3]. - ASLO titres have no role in the diagnosis or monitoring of ankylosing spondylitis. *Osteoarthritis* - **Osteoarthritis** is a degenerative joint disease characterized by cartilage breakdown, typically diagnosed based on clinical presentation, physical examination, and imaging findings. - It is not an inflammatory or autoimmune condition and is not associated with streptococcal infections or ASLO titres.

Question 1356: Infective endocarditis is least common in whom?

A. ASD. (Correct Answer)
B. Mitral stenosis.
C. VSD.
D. Aortic stenosis.

Explanation: ***ASD*** - Infective endocarditis is **least common** in atrial septal defects (ASDs) because the low-pressure, laminar flow across the defect does not typically create the turbulent jet lesions that predispose to vegetations. - While vegetations can form on damaged endothelium, the **absence of high-pressure gradients** makes it less likely [1]. *Mitral stenosis* - **Mitral stenosis** can increase the risk of infective endocarditis, particularly when associated with **severe valvular calcification** or **rheumatic heart disease**. - The turbulent flow and predisposition to atrial fibrillation can contribute to endothelial damage and vegetation formation [1]. *VSD* - **Ventricular septal defects (VSDs)** are considered a **high-risk congenital heart lesion** for infective endocarditis due to the turbulent blood flow from the left ventricle to the right ventricle [1]. - The high-velocity jet can cause **endothelial injury**, making the area susceptible to bacterial adherence and vegetation formation. *Aortic stenosis* - **Aortic stenosis** is a significant risk factor for infective endocarditis, especially in **bicuspid aortic valves** or those with **degenerative calcification** [1]. - The turbulent flow across the stenotic valve creates a predisposition to valve damage and subsequent bacterial adherence.

Question 1357: Which of the following pathogens is commonly associated with respiratory infections in patients with HIV?

A. Pneumocystis jirovecii (Correct Answer)
B. Streptococcus pneumoniae
C. Haemophilus influenzae
D. All of the options

Explanation: ***Pneumocystis jirovecii*** - **Pneumocystis pneumonia (PCP)**, caused by *Pneumocystis jirovecii*, is a classic opportunistic infection in patients with **HIV**, especially those with **CD4 counts below 200 cells/µL** [1]. - It presents as a diffuse interstitial pneumonia with symptoms like **fever**, **cough**, and **dyspnea** [1]. *Haemophilus influenzae* - While *Haemophilus influenzae* can cause **respiratory infections** in HIV patients, it is more commonly associated with exacerbations of **chronic obstructive pulmonary disease (COPD)** or **bronchiectasis**. - It does not typically cause the severe, diffuse pneumonia seen with *Pneumocystis jirovecii* in immunocompromised individuals. *Streptococcus pneumoniae* - **Streptococcus pneumoniae** is a common cause of **bacterial pneumonia** in the general population, and its incidence is also increased in HIV-infected individuals due to impaired immune function [1]. - However, it primarily causes **lobar pneumonia** and is not specifically considered an AIDS-defining opportunistic infection like *Pneumocystis jirovecii*. *All of the options* - Although all three pathogens can cause respiratory infections in HIV patients, *Pneumocystis jirovecii* is the most commonly and uniquely associated opportunistic pathogen causing severe pneumonia in immunocompromised individuals, especially those with advanced HIV disease [1]. - The question asks for the pathogen **commonly associated** with respiratory infections, which in the context of HIV, often points to opportunistic infections specific to immune compromise.

Question 1358: Most common cause of lung abscess?

A. Oral anaerobes (Correct Answer)
B. Staphylococcus aureus
C. Klebsiella pneumoniae
D. Mycobacterium tuberculosis

Explanation: ***Oral anaerobes*** - **Aspiration of oropharyngeal contents** into the lungs is the most common mechanism for lung abscess formation, especially in patients with impaired consciousness or dysphagia. - The aspirated material frequently contains a high concentration of **anaerobic bacteria** from the oral flora, such as *Bacteroides*, *Prevotella*, *Fusobacterium*, and *Peptostreptococcus* species, which thrive in the low-oxygen environment of compromised lung tissue. *Staphylococcus aureus* - While *S. aureus* can cause lung abscesses, particularly in the context of **hematogenous dissemination** (e.g., from endocarditis or intravenous drug use) or in hospitalized patients, it is not the most common causative agent overall. - *S. aureus* infections tend to be more acute and severe, often leading to **necrotizing pneumonia** and multiple small abscesses rather than a single large cavitary lesion. *Klebsiella pneumoniae* - *Klebsiella pneumoniae* is a significant cause of **severe pneumonia** and lung abscess, particularly in individuals with **alcoholism** or **diabetes mellitus**. - It often produces a characteristic **"currant jelly" sputum** due to mucoid capsule production, but it is less common than aspiration-related anaerobic infections. *Mycobacterium tuberculosis* - *Mycobacterium tuberculosis* causes **tuberculosis**, which can lead to cavitary lung lesions, but these are typically **granulomas** with central caseous necrosis rather than true pyogenic abscesses. - While it can present with similar radiographic findings, the pathogenesis and typical clinical course differ significantly from those of a bacterial lung abscess.

Question 1359: Roth spots are specifically associated with which condition?

A. Papilledema
B. Diabetes
C. Infective endocarditis (Correct Answer)
D. Hypertension

Explanation: ***Infective endocarditis*** - **Roth spots** are retinal hemorrhages with a pale center, typically caused by **immune complex deposition** or **embolism** from infective endocarditis. - Their presence is a classic **ophthalmologic sign** associated with this serious infection of the heart valves. *Papilledema* - This condition involves **optic disc swelling** due to increased intracranial pressure, not retinal hemorrhages with pale centers. - It would typically manifest with visual disturbances like transient vision loss, not specific vascular lesions. *Diabetes* - **Diabetic retinopathy** involves microaneurysms, hemorrhages, and exudates, but Roth spots are not a characteristic feature. - Retinal changes in diabetes are primarily due to **microvascular damage** from chronic hyperglycemia. *Hypertension* - **Hypertensive retinopathy** can cause retinal hemorrhages, cotton wool spots, and arteriolar narrowing. - However, the specific appearance of Roth spots with a pale center is not characteristic of hypertensive retinopathy.

Question 1360: A man presents with fever, weight loss, and cough; the Mantoux test reads an induration of 17 x 19 mm, and sputum cytology is negative for acid-fast bacilli. What is the most likely diagnosis?

A. Pulmonary tuberculosis (Correct Answer)
B. Histoplasmosis
C. Influenza
D. Bacterial pneumonia

Explanation: ***Pulmonary tuberculosis*** - The combination of **fever**, **weight loss**, and **cough** are classic symptoms of tuberculosis [1]. - A **Mantoux induration of 17x19 mm** indicates a significant cell-mediated immune response to *Mycobacterium tuberculosis*, supporting the diagnosis even with initial negative sputum cytology [2]. *Histoplasmosis* - While it can cause fever, weight loss, and cough, a **positive Mantoux test** is not characteristic of histoplasmosis. - Diagnosis typically involves fungal cultures, serology, or antigen detection, not tuberculin skin testing. *Influenza* - Influenza is an **acute viral infection** presenting with sudden onset of fever, cough, and myalgia, but **chronic weight loss** is not a typical feature. - The **Mantoux test** being positive does not point towards influenza. *Bacterial pneumonia* - This typically presents with an **acute onset** of fever, productive cough, and dyspnea, while **weight loss** and a **positive Mantoux test** are not typical findings. - It rapidly responds to antibiotics, unlike the more chronic presentation suggested here.

Practice by Chapter

Principles of Antimicrobial Therapy

Practice Questions

Fever of Unknown Origin

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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.)

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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

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Emerging and Re-emerging Infections

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Antimicrobial Resistance

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Vaccination Principles

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