Infectious Diseases Practice Questions

Q: Color of diphtheretic membrane is -

Grey. The diphtheritic membrane typically appears **grey** or grayish-white due to fibrin, dead cells, bacteria, and inflammatory exudate [1]. This characteristic color is a classic diagnostic feature of **diphtheria**. [1] *Cream* - A cream color is not typically associated with the diphtheritic membrane, which has a more distinct grayish hue. - While some membranes might have a lighter appearance, it's not the primary descriptor. *White* - Although the membrane can be described as grayish-white, pure white is not the most accurate or common description. - The presence of necrotic tissue and blood often gives it a darker, more mottled appearance. *Yellow* - A yellow color is not typical for a diphtheritic membrane and would suggest other types of exudate or conditions. - Yellow exudates are more often associated with purulent infections.

Q: A positive tuberculin test is indicated by an area of induration of

>10mm in diameter. ***>10mm in diameter*** - For individuals with no known risk factors for TB, an induration of **≥10 mm** is generally considered a **positive tuberculin skin test (TST)**, indicating past exposure to *Mycobacterium tuberculosis*. [1] - This size threshold helps differentiate actual immune responses from non-specific reactions in the general population. *<5mm in diameter* - An induration of **<5 mm** is typically considered **negative** in most populations, indicating no significant immune response to tuberculin. - However, in specific high-risk groups (e.g., HIV-positive individuals, recent contacts of TB patients), an induration of **≥5 mm** might be considered positive. [1] *No induration* - The absence of any induration indicates a **negative tuberculin test**, meaning there is no detectable immune response to the *Mycobacterium tuberculosis* antigens. - This suggests the individual has likely not been exposed to TB or has successfully cleared a prior infection without developing a measurable immune memory. *6-9mm in diameter* - For people with **no risk factors** for TB, this size is generally considered **negative**, indicating no significant immune response. - In certain high-risk groups (e.g., recent immigrants from high-prevalence countries, IV drug users, residents/employees of high-risk settings), an induration of **≥5 mm** can be considered positive. [1]

Q: An acutely ill 18-year-old female is brought to the emergency department. The patient is febrile and markedly hypotensive, and her mental status is obtunded. Numerous petechial and purpuric hemorrhages are scattered over the trunk, and aspiration of a lesion reveals neutrophils engulfing gram-negative diplococci. Serum sodium is markedly decreased, and serum potassium is increased. Coagulation testing reveals increased prothrombin time, activated partial thromboplastin time, and fibrin-fibrinogen split products. Which of the following is most likely?

Waterhouse-Friderichsen syndrome. ***Waterhouse-Friderichsen syndrome*** - The combination of **rapidly progressing sepsis** with **meningococcal infection** (gram-negative diplococci), widespread **petechiae/purpura**, **adrenal hemorrhage/insufficiency** (leading to **hyponatremia**, **hyperkalemia**, and **hypotension**), and **DIC** is classic for Waterhouse-Friderichsen syndrome. - This syndrome represents a severe, often fatal, complication of **meningococcemia** characterized by overwhelming bacterial sepsis and bilateral massive hemorrhage into the adrenal glands. *Conn syndrome* - This syndrome is characterized by **primary hyperaldosteronism**, typically presenting with **hypertension**, **hypokalemia**, and **metabolic alkalosis**. - The patient's presentation of **hypotension**, **hyperkalemia**, **febrile illness**, and **DIC** is inconsistent with Conn syndrome. *Neuroblastoma* - This is a **childhood cancer** originating from neuroendocrine cells, primarily in the adrenal medulla or sympathetic ganglia. - While it can cause adrenal masses, it does not present with **acute severe sepsis**, **petechial rash**, or **DIC** as the primary features in an 18-year-old. *Hyperprolactinoma* - This is a **pituitary adenoma** that secretes excessive prolactin, causing symptoms like **galactorrhea**, **amenorrhea**, and **infertility**. - It has no association with **acute sepsis**, **DIC**, **adrenal insufficiency**, or the fulminant presentation described in the patient.

Q: Post transplant lymphoma most commonly associated with:

Epstein-Barr virus. ***Epstein-Barr virus*** - **EBV** is strongly implicated in the pathogenesis of **post-transplant lymphoproliferative disorder (PTLD)**, especially in patients receiving immunosuppressive therapy [1]. - The immune suppression post-transplant allows for uncontrolled B-cell proliferation driven by latent EBV infection, leading to lymphoma [2]. *HHV-6* - While HHV-6 can cause reactivation and complications in transplant recipients, it is **not commonly associated** with lymphoma development. - Its clinical manifestations usually include **fever, rash, encephalitis**, and bone marrow suppression. *Herpes simplex* - **HSV** infections are common in transplant patients due to immunosuppression, presenting as mucocutaneous lesions [3]. - However, HSV is **not a known oncogenic virus** that directly contributes to the development of post-transplant lymphoma. *Cytomegalo virus* - **CMV** is a significant pathogen in transplant recipients, causing various syndromes like pneumonitis, colitis, and retinitis [3]. - Although CMV can cause **indirect immunomodulatory effects**, it is not a primary cause of post-transplant lymphoma, unlike EBV.

Q: The antistreptolysin O (ASO) titer is used in the diagnosis of:

Acute rheumatic fever. ***Acute rheumatic fever*** - The **ASO titer** measures antibodies against *Streptolysin O*, a toxin produced by **Group A Streptococcus** (*Streptococcus pyogenes*). - Elevated ASO titers indicate a recent streptococcal infection, which is the precursor to **acute rheumatic fever** [1]. *Osteoarthritis* - This condition is a **degenerative joint disease** primarily caused by wear and tear on cartilage. - It is not associated with microbial infections or immunological responses related to streptococcal antibodies. *Ankylosing spondylitis* - This is a **chronic inflammatory disease** primarily affecting the spine and sacroiliac joints. - It is strongly associated with the **HLA-B27 gene** and not with streptococcal infections. *Acute rheumatoid arthritis* - This is an **autoimmune disease** characterized by chronic inflammation of the synovium, leading to joint damage [2]. - It is typically associated with **rheumatoid factor (RF)** and **anti-citrullinated peptide antibodies (ACPA)**, not ASO titers.

Q: True about Mantoux is -

False negative in fulminant diseases. ***False negative in fulminant diseases*** - In **fulminant diseases** such as **miliary tuberculosis** or severe **immunosuppression**, the body's immune response may be too weak to mount a detectable reaction to the tuberculin, leading to a **false negative result**. - This occurs because the cell-mediated immunity, which is responsible for the Mantoux reaction, is compromised. *If once done, next time it is always positive* - This is incorrect as a positive Mantoux test indicates **prior exposure** to *Mycobacterium tuberculosis* or **BCG vaccination**, but the immune response can wane over time or be affected by immunosuppression. - Subsequent tests can be negative if the immune memory fades or if the individual's immune system is compromised. *Results are given in terms of positive & negative* - The results are interpreted based on the **diameter of induration** (hardening) measured in millimeters, not simply as positive or negative. - The threshold for a positive result varies depending on the individual's risk factors and clinical context. *Indurations given in terms of length & breadth* - The **induration** (palpable raised area) is measured across its **diameter** in millimeters at its widest point, not in terms of separate length and breadth measurements. - Only the induration is measured, not any surrounding erythema (redness).

Q: A 40-year-old man underwent kidney transplantation. Two months after transplantation, he developed fever and features suggestive of bilateral diffuse interstitial pneumonia. Which of the following is the most likely etiologic agent?

Cytomegalovirus. ***Cytomegalovirus*** - **CMV infection** is very common and a frequent opportunistic infection in **immunosuppressed solid organ transplant recipients**, especially within the first few months post-transplant [1]. - **CMV pneumonitis**, characterized by diffuse interstitial pneumonia and fever, is a classic presentation of CMV disease in this patient population [1]. *Varicella zoster virus* - While VZV can cause serious infections in immunosuppressed individuals, **pneumonia due to VZV** is typically part of a disseminated disease and less common than CMV pneumonitis in transplant recipients. - **Cutaneous vesicular lesions** would usually precede or accompany VZV pneumonia, which are not mentioned here. *Herpes simplex virus* - HSV can cause severe mucocutaneous infections in immunocompromised patients, but **HSV pneumonia** is rare and usually manifests as tracheobronchitis or a focal necrotizing pneumonia, not typically diffuse interstitial. - **Esophagitis or encephalitis** are more common serious manifestations of HSV in this population than primary pneumonitis. *Epstein-barr virus* - EBV is primarily associated with **post-transplant lymphoproliferative disorder (PTLD)** in transplant recipients, which can involve the lungs. - While PTLD can manifest with fever and pulmonary infiltrates, **diffuse interstitial pneumonia** solely due to primary EBV infection is less characteristic than for CMV.

Q: The CSF findings in TB meningitis include –

Low sugar + high protein and Lymphocytosis. ***Low sugar + high protein and Lymphocytosis*** - **Tuberculous meningitis** typically presents with **low CSF glucose** because the infecting *Mycobacterium tuberculosis* consumes glucose [2]. - There is a characteristic **high CSF protein** due to inflammation and increased permeability of the blood-brain barrier [2], along with a **lymphocytic pleocytosis** as the immune response is often T-cell mediated [1]. *High sugar + high chloride* - This combination is not characteristic of **Tuberculous meningitis** or any common form of meningitis. - **CSF glucose** is typically low in bacterial and tuberculous meningitis due to consumption by microbes [2]. *High sugar + low protein* - **High CSF glucose** and **low protein** are not consistent with **Tuberculous meningitis** or other forms of meningitis. - In meningitis, inflammation generally leads to elevated protein levels [2]. *Low sugar + high protein and Lymphopenia* - While **low sugar** and **high protein** are typical in **Tuberculous meningitis**, **lymphopenia** (low lymphocyte count) is incorrect. - The inflammatory response in **Tuberculous meningitis** is primarily characterized by a **lymphocytic pleocytosis**, meaning an increase in lymphocytes [1].

Q: Pneumococcal meningitis is associated with the following CSF findings:

Pleocytosis with high protein and low sugar. ***Pleocytosis with high protein and low sugar*** - **Bacterial meningitis**, such as that caused by pneumococcus, typically presents with **neutrophilic pleocytosis** (increased white blood cells, predominantly neutrophils) due to the inflammatory response. - The high bacterial load and increased protein leakage from inflamed meninges lead to **elevated CSF protein**, while bacterial consumption of glucose results in **low CSF glucose** [1]. *Pleocytosis with low protein and low sugar* - While **pleocytosis** and **low sugar** (hypoglycorrhachia) are characteristic of bacterial meningitis, **low protein** is not. - Bacterial infections typically cause increased protein in the CSF due to inflammation and breakdown of the blood-brain barrier [1]. *Lymphocytosis with low protein and low sugar* - **Lymphocytosis** is usually seen in **viral or fungal meningitis**, not bacterial meningitis, where neutrophils predominate [1]. - **Low protein** is inconsistent with bacterial meningitis, which typically causes **high protein** in the CSF. *Lymphocytosis with high protein and low sugar* - This combination is partially inconsistent; while **high protein** and **low sugar** can be seen in some severe or chronic forms of meningitis, **lymphocytosis** is not the primary cell response in **acute bacterial meningitis**. [1] - **Lymphocytosis** would typically suggest a viral, fungal, or tuberculous etiology.

Q: A blood donor is not considered for safe transfusion if he has:

HBsAg +ve and IgM anti-HBc +ve. ***HBsAg +ve and IgM anti-HBc +ve*** - A positive **HBsAg** indicates current hepatitis B infection, making the donor unsuitable for transfusion due to the risk of transmission [2]. - The presence of **IgM anti-HBc** further confirms a recent or acute infection, enhancing the risk of infectivity [2], [3]. *Anti-HBc +ve* - A positive **anti-HBc** (total) alone can indicate a past resolved infection or chronic infection, but does not always rule out donation, especially if HBsAg is negative and anti-HBs is positive [3]. - In many settings, donors with isolated anti-HBc positive results might be deferred, but it's not as definitive a contraindication as HBsAg positivity. *Anti-HBsAg +ve* - A positive **anti-HBsAg** (HBsAb) indicates immunity to hepatitis B, either due to vaccination or past resolved infection [3]. - Donors with only anti-HBsAg positivity are generally considered safe for transfusion as they are not infectious and may even provide protective antibodies [1]. *Anti-HBsAg and anti-HBc (+)ve* - This profile typically indicates a **resolved hepatitis B infection** with established immunity [3]. - Such individuals are considered safe donors as they are not actively infected and pose no risk of transmitting hepatitis B [1].

Question 1

Color of diphtheretic membrane is -

Accepted Answer

Grey

Answer

Cream

Answer

White

Answer

Yellow

Question 2

A positive tuberculin test is indicated by an area of induration of

Accepted Answer

>10mm in diameter

Answer

<5mm in diameter

Answer

No induration

Answer

6-9mm in diameter

Question 3

An acutely ill 18-year-old female is brought to the emergency department. The patient is febrile and markedly hypotensive, and her mental status is obtunded. Numerous petechial and purpuric hemorrhages are scattered over the trunk, and aspiration of a lesion reveals neutrophils engulfing gram-negative diplococci. Serum sodium is markedly decreased, and serum potassium is increased. Coagulation testing reveals increased prothrombin time, activated partial thromboplastin time, and fibrin-fibrinogen split products. Which of the following is most likely?

Accepted Answer

Waterhouse-Friderichsen syndrome

Answer

Conn syndrome

Answer

Neuroblastoma

Answer

Hyperprolactinoma

Question 4

Post transplant lymphoma most commonly associated with:

Accepted Answer

Epstein-Barr virus

Answer

HHV-6

Answer

Herpes simplex

Answer

Cytomegalo virus

Question 5

The antistreptolysin O (ASO) titer is used in the diagnosis of:

Accepted Answer

Acute rheumatic fever

Answer

Osteoarthritis

Answer

Ankylosing spondylitis

Answer

Acute rheumatoid arthritis

Question 6

True about Mantoux is -

Accepted Answer

False negative in fulminant diseases

Answer

If once done, next time it is always positive

Answer

Results are given in terms of positive & negative

Answer

Indurations given in terms of length & breadth

Question 7

A 40-year-old man underwent kidney transplantation. Two months after transplantation, he developed fever and features suggestive of bilateral diffuse interstitial pneumonia. Which of the following is the most likely etiologic agent?

Accepted Answer

Cytomegalovirus

Answer

Varicella zoster virus

Answer

Herpes simplex virus

Answer

Epstein-barr virus

Question 8

The CSF findings in TB meningitis include –

Accepted Answer

Low sugar + high protein and Lymphocytosis

Answer

High sugar + high chloride

Answer

High sugar + low protein

Answer

Low sugar + high protein and Lymphopenia

Question 9

Pneumococcal meningitis is associated with the following CSF findings:

Accepted Answer

Pleocytosis with high protein and low sugar

Answer

Pleocytosis with low protein and low sugar

Answer

Lymphocytosis with low protein and low sugar

Answer

Lymphocytosis with high protein and low sugar

Question 10

A blood donor is not considered for safe transfusion if he has:

Accepted Answer

HBsAg +ve and IgM anti-HBc +ve

Answer

Anti-HBc +ve

Answer

Anti-HBsAg +ve

Answer

Anti-HBsAg and anti-HBc (+)ve

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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