Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 1301: The most common cause of sporadic viral encephalitis is what?

A. Japanese B encephalitis
B. Herpes simplex encephalitis (Correct Answer)
C. Human immunodeficiency virus encephalitis
D. Rubeola encephalitis

Explanation: ***Herpes simplex encephalitis*** - **Herpes simplex virus (HSV)**, particularly **HSV-1**, is the most frequent cause of **sporadic viral encephalitis** globally. - It often presents with characteristic temporal lobe involvement, leading to **focal neurological deficits** and **seizures** [1]. *Japanese B encephalitis* - This is a prominent cause of **epidemic viral encephalitis** in Asia, primarily affecting children, but not the most common cause of **sporadic cases**. - It is transmitted by **mosquitoes** and typically has a seasonal pattern. *Human immunodeficiency virus encephalitis* - HIV can cause **encephalopathy** and dementia in advanced stages, but it is not typically characterized as **acute viral encephalitis** [1]. - The neurological manifestations of HIV are more chronic and progressive rather than an acute inflammatory process of the brain [1]. *Rubeola encephalitis* - **Rubeola (measles virus)** can cause acute post-infectious encephalomyelitis or the rare, fatal, late-onset condition **subacute sclerosing panencephalitis (SSPE)**. - While serious, these conditions are not the most common cause of **sporadic acute viral encephalitis** in the general population.

Question 1302: A truck driver, who is HIV-positive, presented with a history of fever since four weeks, and a dry cough, as well as a history of weight loss of about 10 kg. X-ray shows bilateral reticulonodular infiltrates. The most likely diagnosis is:

A. Tuberculosis
B. Pneumocystis pneumonia (Correct Answer)
C. Pneumococcal pneumonia
D. Interstitial lung disease

Explanation: ***Pneumocystis pneumonia*** - This patient, an HIV-positive individual with prolonged **fever**, **dry cough**, significant **weight loss**, and **bilateral reticulonodular infiltrates** on X-ray, presents with a classic clinical picture for **Pneumocystis jirovecii pneumonia (PCP)**, which is an opportunistic infection common in immunocompromised individuals [1]. - The **dry cough** and **diffuse bilateral infiltrates** are highly characteristic of PCP, especially in the context of HIV and unexplained weight loss, suggesting advanced HIV disease [1]. *Tuberculosis* - While **tuberculosis (TB)** is common in HIV-positive individuals and can cause fever, weight loss, and cough, the X-ray finding of **bilateral reticulonodular infiltrates** is less typical for primary pulmonary TB, which often presents with cavitary lesions or focal infiltrates [1]. - The **cough** in TB is often productive, whereas in this case, it is described as dry. *Pneumococcal pneumonia* - **Pneumococcal pneumonia** typically presents with an **acute onset** of high fever, productive cough, and pleuritic chest pain, and chest X-rays usually show **lobar consolidation** [1]. - The patient's presentation of a four-week history and dry cough does not align with the typical acute bacterial pneumonia caused by *Streptococcus pneumoniae*. *Interstitial lung disease* - **Interstitial lung disease (ILD)** usually presents with **progressive dyspnea** and a dry cough over a longer period, often without significant fever or rapid weight loss unless it's an acute exacerbation [1]. - While ILD can cause reticulonodular infiltrates, the acute febrile illness and significant weight loss point more towards an infectious etiology, especially in an HIV-positive patient [1].

Question 1303: Intestinal perforation in typhoid occurs commonly in which part of the intestine?

A. Jejunum
B. Duodenum
C. Cecum
D. Ileum (Correct Answer)

Explanation: Ileum - The **ileum** is the most common site of typhoid perforation due to the highest concentration of **Peyer's patches** in this region. - Salmonella typhi preferentially invades and proliferates within these lymphoid aggregates, leading to **necrosis** and subsequent perforation. Jejunum - The **jejunum** has fewer Peyer's patches compared to the ileum, making it a much less common site for typhoid-related complications like perforation. - While inflammation can occur, the extensive lymphoid hyperplasia and subsequent ulceration seen in the ileum are less pronounced here. Duodenum - The **duodenum** is rarely affected by typhoid perforation, as it lacks significant Peyer's patches, which are the primary target for Salmonella typhi. - Perforations in the duodenum are generally associated with other causes, such as **peptic ulcer disease**. Cecum - While the **cecum** is part of the large intestine and contains lymphoid tissue, it is not the primary site of attack for Salmonella typhi leading to perforation. - The characteristic pathology of typhoid, involving extensive ulceration of Peyer's patches, is most prominent in the terminal ileum before the ileocecal valve.

Question 1304: A patient presents with clustered, white lesions on the buccal mucosa, typically near the upper molars. These lesions are pathognomonic for measles. What are these lesions called?

A. Leukoplakia
B. Koplik spots (Correct Answer)
C. Kaposi spots
D. None of the options

Explanation: ***Koplik spots*** - These are pathognomonic for **measles (rubeola)** and appear as small, **white or bluish-white lesions** on an erythematous base on the buccal mucosa. - They typically precede the characteristic rash of measles by 1-2 days, making them a crucial early diagnostic sign. *Leukoplakia* - Refers to **thickened, white patches** on the mucous membranes that cannot be scraped off and are often precancerous. - These lesions are usually associated with chronic irritation (e.g., tobacco use) and are not a feature of viral infections like measles. *Kaposi spots* - This term is **not typically used** to describe oral lesions, particularly in the context of measles. - Kaposi sarcoma involves **purple or brown skin lesions** associated with HHV-8 infection, commonly seen in immunocompromised individuals. *None of the options* - This option is incorrect because **Koplik spots** accurately describe the buccal mucosal lesions pathognomonic for measles.

Question 1305: Pneumothorax could be a complication of what?

A. Pneumococcal pneumonia
B. Klebsiella pneumonia
C. Staphylococcal pneumonia (Correct Answer)
D. Viral pneumonia

Explanation: ***Staphylococcal pneumonia*** - *Staphylococcus aureus* is known for causing **necrotizing pneumonia**, forming abscesses and **cavitary lesions** that can rupture into the pleural space. - This rupture leads to a **bronchopleural fistula** and subsequent development of a **pneumothorax** [2]. *Pneumococcal pneumonia* - This is the most common cause of **community-acquired pneumonia** but typically causes **lobar consolidation** [1]. - It is rarely associated with necrotizing changes or significant pleural complications like pneumothorax, though **empyema** can occur [2]. *Klebsiella pneumonia* - Often causes severe, **necrotizing pneumonia**, particularly in debilitated or alcoholic individuals, but is more commonly associated with **abscess formation** within the lung parenchyma [3]. - While lung destruction can occur, pneumothorax is a less frequent direct complication compared to cavitary lesions seen in staphylococcal infections. *Viral pneumonia* - Typically causes **interstitial inflammation** and diffuse involvement of the lung parenchyma [4]. - It does not usually lead to significant tissue necrosis or cavitation that would predispose to a pneumothorax.

Question 1306: Kaposi's sarcoma (KS) usually occurs when CD4+ lymphocyte counts are what?

A. CD4+ lymphocyte counts above 600
B. CD4+ lymphocyte counts between 1000-2000
C. CD4+ lymphocyte counts above 2000
D. CD4+ lymphocyte counts below 200 (Correct Answer)

Explanation: ***CD4+ lymphocyte counts below 200*** - **Kaposi's sarcoma (KS)** is an **AIDS-defining illness** and typically appears in individuals with severe immunocompromise [3]. - A CD4 count below **200 cells/µL** indicates a severely compromised immune system, making the patient susceptible to opportunistic infections and cancers like KS [1], [2]. *CD4+ lymphocyte counts above 600* - CD4 counts above **600 cells/µL** generally indicate a relatively healthy immune system [2]. - While HIV infection might be present, the risk of developing KS at this CD4 level is very low. *CD4+ lymphocyte counts between 1000-2000* - Normal CD4 counts in healthy individuals are typically between **500 and 1500 cells/µL** [2]. Counts in the 1000-2000 range are considered normal or even elevated, indicating a robust immune system. - Individuals with such CD4 counts are highly unlikely to develop Kaposi's sarcoma, as this cancer is associated with significant immunodeficiency [1]. *CD4+ lymphocyte counts above 2000* - CD4 counts above **2000 cells/µL** are significantly higher than the normal range and indicate a very strong immune system. - Kaposi's sarcoma is a disease of immunodeficiency, so it would not be expected in individuals with such high CD4 counts [1].

Question 1307: What is the diagnostic criterion for sputum-positive tuberculosis (TB)?

A. At least 1 sputum sample positive for AFB (Correct Answer)
B. BACTEC positive
C. No positive samples
D. 2 out of 3 sputum samples positive

Explanation: The definition of sputum-positive TB, particularly in initial diagnosis, generally requires at least one **acid-fast bacilli (AFB) smear-positive** sputum sample [1]. This criterion is crucial for guiding initial treatment strategies and public health interventions for **infectious TB** [1]. While a BACTEC-positive result confirms the presence of **Mycobacterium tuberculosis**, a rapid AFB smear positive result is often the initial criterion for "sputum-positive" classification for immediate management [2]. While some guidelines or clinical contexts might emphasize multiple positive samples for confirmation, the widely accepted minimum for sputum-positive TB is **at least one positive AFB smear** [1].

Question 1308: Which of the following is NOT a complication of Typhoid ulcers?

A. Stricture
B. Endocarditis (Correct Answer)
C. Haemorrhage
D. Perforation

Explanation: ### Endocarditis - **Endocarditis** is primarily associated with **bacterial infections** of the heart valves, not typically a direct complication of **Typhoid ulcers** [2]. - While systemic infections can rarely lead to endocarditis, Typhoid ulcers themselves are a localized gastrointestinal pathology. ### Perforation - **Perforation** is a serious complication of deep Typhoid ulcers, particularly in the **ileum**, where the **Peyer's patches** become necrotic [1]. - This leads to the leakage of bowel contents into the peritoneal cavity, causing **peritonitis**. ### Stricture - **Stricture formation** can occur in the intestine as a result of the healing process of deep and extensive Typhoid ulcers. - The fibrotic tissue laid down during repair can narrow the lumen of the bowel, leading to **obstruction**. ### Haemorrhage - **Haemorrhage** is a common and potentially life-threatening complication of typhoid ulcers, occurring when the ulcer erodes into a **blood vessel** [1]. - This can manifest as **melena** or **hematochezia**, indicating gastrointestinal bleeding.

Question 1309: Risk of HIV transmission is not seen with

A. Platelets
B. Leukocytes vaccines
C. Whole blood
D. Plasma derived hepatitis B vaccine (Correct Answer)

Explanation: The original text with [1] citations added (ONLY for relevant references) - **Plasma-derived hepatitis B vaccines** undergo extensive purification and inactivation processes, which effectively eliminate the risk of **HIV transmission** [1]. - The manufacturing process ensures that any potential viral contaminants, including HIV, are **inactivated** or removed, making the vaccine safe [1]. *Whole blood* - **Whole blood** transfusions carry a significant risk of **HIV transmission** if the donor is infected and the blood is not properly screened [2]. - HIV can survive in whole blood, making it a direct conduit for transmission from an infected donor to a recipient [1], [2]. *Platelets* - **Platelets** are derived from whole blood and can contain viable **HIV particles**, posing a risk of transmission during transfusion [2]. - Although the risk might be slightly lower than with whole blood due to processing, it is still a recognized route for HIV transmission [1]. *Leukocytes vaccines* - The term "leukocytes vaccines" is vague, but if it refers to products containing **leukocytes** (white blood cells), these cells are a primary host for **HIV**. - Components directly derived from or containing viable leukocytes from an infected individual would carry a high risk of HIV transmission.

Question 1310: What is the route of administration for the tuberculin test?

A. Intramuscular
B. Intradermal (Correct Answer)
C. Subcutaneous
D. None of the options

Explanation: ***Intradermal*** - The tuberculin test (also known as the **Mantoux test** or **PPD test**) involves injecting a small amount of **purified protein derivative (PPD)** into the **dermis layer** of the skin [1]. - This route allows for a localized immune response to be observed as an area of **induration** (a palpable, raised, hardened area) if the person has been exposed to *Mycobacterium tuberculosis* [1]. *Intramuscular* - This route involves injecting into a **muscle**, which is used for many vaccines and medications that need to be absorbed into the bloodstream. - It would not allow for the localized skin reaction necessary to interpret the tuberculin test. *Subcutaneous* - This route involves injecting into the **fatty tissue** just under the skin. - While close to the surface, it is not as precise as an intradermal injection for eliciting the specific localized immune response required for tuberculin testing. *None of the options* - This option is incorrect because the intradermal route is a standard and recognized method for administering the tuberculin test.

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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