Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 971: Super infection is common in:

A. Narrow spectrum antibiotics
B. Immuno compromised host
C. Nutritional deficiency
D. Broad spectrum antibiotics (Correct Answer)

Explanation: ***Broad spectrum antibiotics*** - **Broad-spectrum antibiotics** disrupt a wide range of normal flora, including beneficial bacteria, which creates an ecological void that opportunistic pathogens can then colonize [1]. - This disruption allows resistant organisms or fungi (e.g., *Clostridium difficile*, *Candida*) to proliferate unchecked, leading to a **superinfection**. *Narrow spectrum antibiotics* - **Narrow-spectrum antibiotics** target a specific type of bacteria, causing less disruption to the overall normal microbial flora [1]. - Due to their selective action, they are less likely to create the ecological imbalance that predisposes to superinfections. *Immuno compromised host* - While **immunocompromised hosts** are certainly prone to various opportunistic infections, superinfection specifically refers to a new infection occurring during or after treatment for a prior infection, often facilitated by antibiotic use [2]. - In this context, the primary cause of superinfection lies with the antibiotic's effect on flora, rather than the host's immune status directly initiating it. *Nutritional deficiency* - **Nutritional deficiencies** can impair immune function and increase susceptibility to infections in general. - However, they do not directly cause or predispose to superinfections in the specific sense of antibiotic-induced changes in microbial flora.

Question 972: What is the most common site for extrapulmonary tuberculosis?

A. GIT
B. Pleura
C. Lymph nodes (Correct Answer)
D. Brain

Explanation: ***Lymph nodes*** - **Lymphatic involvement** is the most frequent manifestation of extrapulmonary tuberculosis (EPTB), particularly in immunocompromised individuals [1]. - It often presents as **painless lymphadenopathy**, commonly in the cervical region, and can be diagnosed via biopsy and culture [1]. *GIT* - **Gastrointestinal tuberculosis** is relatively rare compared to lymphatic involvement, though it can affect any part of the alimentary canal. - Symptoms are often non-specific, including abdominal pain, weight loss, and changes in bowel habits, which makes diagnosis challenging. *Pleura* - **Pleural tuberculosis** is a common form of EPTB, but it is less frequent than lymph node involvement. - It typically presents as a **pleural effusion** and is often diagnosed by analyzing pleural fluid or biopsy for evidence of *Mycobacterium tuberculosis* [2]. *Brain* - **Central nervous system (CNS) tuberculosis**, including tuberculous meningitis or tuberculoma, is a severe but less common form of EPTB [2]. - It carries significant morbidity and mortality and often requires a high index of suspicion for diagnosis [2].

Question 973: Diarrhea syndrome in an AIDS patient can be due to which of the following? a) Rota virus b) Cryptosporidium c) Adenovirus d) E. coli

A. Cryptosporidium (Correct Answer)
B. Adenovirus
C. Rota virus
D. E. coli

Explanation: ***Cryptosporidium*** - **Cryptosporidium parvum** is a common cause of **chronic, severe, watery diarrhea** in AIDS patients due to their compromised immune system [1]. - Infection can lead to **malabsorption** and significant weight loss in immunocompromised individuals [1]. *Adenovirus* - While adenoviruses can cause **gastroenteritis**, particularly in children, they are generally not a primary cause of severe, chronic diarrhea in AIDS patients. - Other opportunistic pathogens are usually more prevalent and cause more severe disease in immunocompromised hosts. *Rota virus* - **Rotavirus** is a common cause of **acute gastroenteritis** in infants and young children worldwide. - While it can infect immunocompromised individuals, it typically causes self-limiting illness and is less likely than Cryptosporidium to cause persistent, severe diarrhea in AIDS patients. *E. coli* - Various strains of **Escherichia coli** can cause diarrhea, ranging from traveler's diarrhea (e.g., ETEC) to hemorrhagic colitis (e.g., EHEC). - While some E. coli infections can be severe, they are not specifically or predominantly linked to chronic diarrhea in AIDS patients in the way opportunistic pathogens like Cryptosporidium are.

Question 974: Two students from a university dormitory building have contracted meningitis due to Neisseria meningitides. Which of the following students in the dormitory are most likely to benefit from chemoprophylaxis?

A. close contacts only, with oral rifampin (Correct Answer)
B. everybody in the dormitory, with oral rifampin
C. close contacts only, with oral amoxicillin
D. everybody in the dormitory, with oral amoxicillin

Explanation: ***close contacts only, with oral rifampin*** - **Chemoprophylaxis** for *Neisseria meningitidis* is primarily recommended for **close contacts** due to the direct person-to-person transmission mode [1]. - **Oral rifampin** is an effective antibiotic for prophylaxis as it penetrates pharyngeal secretions and eliminates carriage of the bacteria [1]. *everybody in the dormitory, with oral rifampin* - Administering chemoprophylaxis to **everyone** in the dormitory is **excessive** and not indicated, as the risk of transmission is highest among close contacts [1]. - Widespread indiscriminate use of antibiotics like rifampin can contribute to **antibiotic resistance**. *close contacts only, with oral amoxicillin* - While prophylaxis is correctly targeted at **close contacts**, **amoxicillin** is generally **not recommended** for *N. meningitidis* chemoprophylaxis. - Amoxicillin does not reliably eradicate meningococcal carriage from the nasopharynx and is therefore **ineffective** for prophylaxis. *everybody in the dormitory, with oral amoxicillin* - This option is incorrect because both the scope of administration (**everybody in the dormitory**) and the choice of antibiotic (**amoxicillin**) are inappropriate. - **Amoxicillin** is not effective for clearing *N. meningitidis* carriage, and widespread use is not justified for prophylaxis.

Question 975: Most common heart valve involved in IV drug users is

A. Mitral valve
B. Tricuspid Valve (Correct Answer)
C. Pulmonary valve
D. Aortic valve

Explanation: ***Tricuspid Valve*** - The **tricuspid valve** is most commonly affected because intravenous (IV) drug users inject directly into the venous system, and the first valve the bacteria encounter as they return to the heart is the tricuspid valve. - This often leads to **right-sided endocarditis**, a common complication in this population. *Mitral valve* - The **mitral valve** is part of the left side of the heart and is less frequently affected in IV drug users as bacteria would need to traverse the pulmonary circulation first. - Mitral valve endocarditis is more common in non-IV drug users or in patients with pre-existing valvular disease. *Pulmonary valve* - While the **pulmonary valve** is also on the right side of the heart, it is located after the tricuspid valve in the blood flow path, making it less likely to be the initial site of bacterial seeding. [1] - **Infective endocarditis** of the pulmonary valve is extremely rare compared to the tricuspid valve. [1] *Aortic valve* - The **aortic valve** is on the left side of the heart and is typically affected by endocarditis that originates from systemic infections or in patients with underlying valvular abnormalities. - It is much less common for the aortic valve to be the primary site of infection in IV drug users compared to the tricuspid valve, as bacteria would have to bypass the pulmonary circulation and mitral valve first.

Question 976: Following acute pharyngitis, a patient was on broad spectrum antibiotics. One week later he developed watery diarrhoea with a foul odour and abdominal cramps. Antibiotic induced colitis is confirmed. What is the most common cause of antibiotic induced colitis?

A. Esch. coli
B. Clostridium difficile (Correct Answer)
C. Campylobacter jejuni
D. Salmonella

Explanation: ***Clostridium difficile*** - **Clostridium difficile** infection is the most common cause of **antibiotic-induced colitis** [1], leading to symptoms like **watery diarrhea, foul odor**, and **abdominal cramps** [1]. - Antibiotics disrupt the normal gut flora, allowing **C. difficile** to overgrow and produce toxins that damage the colon [1]. *Esch. coli* - While some strains of *E. coli* can cause **diarrhea** (e.g., ETEC, EHEC), it is not the primary cause of antibiotic-induced colitis [2]. - **Esch. coli** diarrhea is typically acquired through contaminated food or water, not antibiotic use [2]. *Campylobacter jejuni* - *Campylobacter jejuni* typically causes **gastroenteritis** with **bloody diarrhea** and **fever**, often from consuming contaminated poultry. - It is not directly associated with **antibiotic-induced colitis** as the primary causative agent. *Salmonella* - **Salmonella** infections usually result from contaminated food and present with **fever, abdominal cramps**, and **diarrhea** (which can be bloody). - It is not the most common pathogen responsible for **antibiotic-induced colitis**.

Question 977: The most common etiology of native valve endocarditis is

A. Enterococcus faecalis
B. Gram negative bacilli
C. Streptococcus viridans (Correct Answer)
D. Staphylococcus aureus

Explanation: ***Streptococcus viridans*** - This group of bacteria is the **most common cause** of native valve endocarditis, accounting for about half of cases [1]. - They typically cause **subacute bacterial endocarditis** in patients with pre-existing heart valve damage [1]. *Enterococcus faecalis* - While a significant cause of endocarditis, particularly in the elderly and those with genitourinary or gastrointestinal procedures, it is **less common** than *Streptococcus viridans* for native valve infections overall [1]. - *Enterococci* are associated with **nosocomial infections** and are often resistant to multiple antibiotics. *Gram negative bacilli* - Gram-negative bacilli, such as *Pseudomonas aeruginosa* or *Escherichia coli*, are **uncommon causes** of native valve endocarditis. - When they do cause endocarditis, it is often associated with immunocompromised states, intravenous drug abuse, or prosthetic valves, and carries a **poor prognosis**. *Staphylococcus aureus* - *Staphylococcus aureus* is a common cause of endocarditis, especially in **intravenous drug users** and those with **prosthetic valves**, or in cases of acute endocarditis [1]. - However, for overall native valve endocarditis, its incidence is **lower than** *Streptococcus viridans*.

Question 978: Break bone fever is ?

A. Kala azar
B. Japanese encephalitis
C. Dengue fever (Correct Answer)
D. Malaria

Explanation: ***Dengue fever*** - **Dengue fever** is commonly known as **break bone fever** due to the severe muscle and joint pain it causes [1]. - This intense body pain is one of the characteristic symptoms, making the name highly descriptive of the patient's experience [1]. *Kala azar* - **Kala azar**, or visceral leishmaniasis, is characterized by **prolonged fever**, significant **weight loss**, **splenomegaly**, and **anemia**. - It does not specifically cause the severe bone and joint pain associated with "break bone fever." *Japanese encephalitis* - **Japanese encephalitis** primarily causes **neurological symptoms** like fever, headache, altered mental status, seizures, and paralysis. - While fever is present, it does not typically manifest with the extreme musculoskeletal pain that would earn it the "break bone fever" moniker. *Malaria* - **Malaria** is characterized by cyclical fevers, chills, sweats, fatigue, and **anemia**. - Although it causes body aches, these are not typically as severe or specific to bone pain as in dengue, and it is not known as "break bone fever."

Question 979: Tuberculin unit is:

A. 0.0001 mg
B. 0.1 mg BCG
C. 1 unit of PPD 3 (Correct Answer)
D. None of the options

Explanation: ***1 unit of PPD 3*** - A **tuberculin unit** is defined as the amount of **purified protein derivative (PPD) containing 5 tuberculin units**, which corresponds to 0.0001 mg of PPD. - While often used interchangeably with **5 TU**, the definition of a single tuberculin unit refers to its biological activity, and in the context of PPD, **1 TU** is a specific measure of potency. *0.0001 mg* - This value represents the mass of **purified protein derivative (PPD) in 5 tuberculin units**, not a single tuberculin unit itself. - It is typically the amount of PPD found in the standard dose used for the **Mantoux tuberculin skin test**. *0.1 mg BCG* - **BCG (Bacillus Calmette-Guérin)** is a vaccine used to prevent tuberculosis, not a component of the tuberculin test. - The amount of BCG is unrelated to the definition of a tuberculin unit, which measures immune response to **Mycobacterium tuberculosis** antigens. *None of the options* - This option is incorrect because **1 unit of PPD 3** correctly refers to a tuberculin unit, which is a standardized measure used in tuberculosis testing.

Question 980: Ludwig angina is usually caused by

A. Streptococci and various mixed anaerobes (Correct Answer)
B. Anaerobic infection by Prevotella and Fusobacterium
C. Paramyxovirus
D. Candida species

Explanation: ***Streptococci and various mixed anaerobes*** - **Ludwig angina** is a rapidly progressive **cellulitis** of the submandibular and sublingual spaces, predominantly caused by bacteria from the oral flora. - The most common pathogens include **alpha-hemolytic streptococci**, along with various **anaerobes** such as *Bacteroides*, *Peptostreptococcus*, and *Fusobacterium* species, reflecting the polymicrobial nature of dental infections that often precede it. *Anaerobic infection by Prevotella and Fusobacterium* - While *Prevotella* and *Fusobacterium* are important **anaerobic components** of the oral flora and can contribute to Ludwig angina, this option is too restrictive. - It omits the crucial role of **aerobic streptococci** which are frequently isolated alongside anaerobes in this infection. *Paramyxovirus* - **Paramyxoviruses** are a family of RNA viruses that cause diseases such as **mumps**, measles, and respiratory syncytial virus infection. - They are responsible for **viral infections** and do not cause bacterial cellulitis like Ludwig angina. *Candida species* - **Candida species** are yeasts that typically cause **fungal infections**, such as oral thrush or systemic candidiasis. - They are generally not primary causative agents of **bacterial cellulitis** such or severe deep neck infections like Ludwig angina.

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Principles of Antimicrobial Therapy

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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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