Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 891: Which component of HBV causes glomerulonephritis?

A. Anti HBs Ag antibody
B. HBc Ag
C. Hbs Ag (Correct Answer)
D. Hbe Ag

Explanation: ### HBs Ag - **Hepatitis B surface antigen (HBsAg)** is a viral protein that can form immune complexes with its corresponding antibody within the body [1]. - These **immune complexes** can deposit in the glomeruli of the kidneys, triggering an inflammatory response that leads to **glomerulonephritis**, particularly **membranous nephropathy** or **membranoproliferative glomerulonephritis**. *Anti HBs Ag antibody* - This antibody usually indicates **immunity** to HBV infection, either from vaccination or resolved infection [1]. - While it forms an immune complex with HBsAg, this typically leads to **clearance of the virus** and does not directly cause glomerulonephritis. *HBc Ag* - **Hepatitis B core antigen (HBcAg)** is located within the viral core and is not typically released into the bloodstream as a free antigen [1]. - Therefore, it is **unlikely to directly form immune complexes** in the circulation that could deposit in the kidney. *HBe Ag* - **Hepatitis B e antigen (HBeAg)** indicates active viral replication and high infectivity. - Although it can be detected in the serum, it is **less commonly implicated** in the direct formation of immune complexes leading to glomerulonephritis compared to HBsAg.

Question 892: Tuberculin positivity means:

A. Resistance to tubercular protein
B. Infection with mycobacterium (Correct Answer)
C. Immunodeficiency
D. Patient suffering from disease

Explanation: ***Infection with mycobacterium*** - Tuberculin positivity, detected by a **positive tuberculin skin test (TST)** or **interferon-gamma release assay (IGRA)**, indicates that an individual has been exposed to and infected with **Mycobacterium tuberculosis** [1]. - This response reflects a **delayed-type hypersensitivity reaction** to tuberculin proteins, signifying the presence of cell-mediated immunity against the pathogen. *Resistance to tubercular protein* - Tuberculin positivity does not signify **resistance**; rather, it indicates prior exposure and the development of an immune response. - While prior infection can offer some protection, it doesn't equate to complete resistance, and individuals can still develop active disease. *Immunodeficiency* - Immunodeficiency would typically lead to a **false-negative** tuberculin test due to an inability to mount an adequate immune response, rather than a positive result. - A positive tuberculin test generally implies a functioning immune system capable of reacting to the bacterial antigens. *Patient suffering from disease* - A positive tuberculin test indicates **infection** with Mycobacterium tuberculosis, but it does **not differentiate** between latent TB infection (LTBI) and active TB disease [2]. - Further diagnostic tests, such as chest X-rays, sputum cultures, and clinical evaluation, are required to establish a diagnosis of active disease.

Question 893: What is the most common viral illness transmitted via homologous blood transfusion?

A. Hepatitis C (HCV)
B. HIV
C. Hepatitis B (HBV) (Correct Answer)
D. Cytomegalovirus (CMV)

Explanation: **Hepatitis B (HBV)** - Although screening has significantly reduced the risk, **Hepatitis B (HBV)** remains a frequently transmitted viral infection through homologous blood transfusion due to its relatively **high viremia** and occassional **'window period'** infections that can evade detection [1]. - HBV also has a significant global prevalence, contributing to its ongoing presence as a risk despite rigorous testing protocols [1]. *Hepatitis C (HCV)* - While historically a leading cause of post-transfusion hepatitis, advanced **nucleic acid amplification testing (NAAT)** has dramatically reduced the risk of HCV transmission via blood products [1]. - The **prevalence of HCV** in the general population coupled with sensitive screening tests means it is now less commonly transmitted than HBV through transfusion [1]. *HIV* - The risk of **HIV transmission** through blood transfusion is exceedingly low in developed countries due to highly effective and sensitive screening methods, including **NAAT** and antibody tests [1]. - While devastating, the **incidence of transfusion-related HIV** is rare due to stringent donor selection and testing [1]. *Cytomegalovirus (CMV)* - **CMV** transmission through blood transfusion is a concern primarily in **immunocompromised recipients** (e.g., neonates, transplant patients) where it can cause significant morbidity. - For the general population, CMV infection from transfusion is often subclinical or mild, and leukoreduction of blood products has further reduced its transmission risk [1].

Question 894: Antecedent diagnosis of Group A streptococcal infection in Acute rheumatic fever can be made by?

A. ASO (Correct Answer)
B. ESR elevation
C. Low C3 levels
D. CRP

Explanation: ***ASO*** - ASO (Antistreptolysin O) titer measures antibodies to **Streptolysin O**, a toxin produced by Group A Streptococcus (GAS), indicating a recent GAS infection. - An elevated or rising ASO titer is a key diagnostic criterion for confirming a preceding GAS infection in the context of **Acute Rheumatic Fever (ARF)** [1]. *ESR elevation* - **Erythrocyte Sedimentation Rate (ESR)** is a non-specific marker of inflammation and will be elevated in ARF, but it does not confirm a preceding GAS infection [2]. - Many inflammatory conditions can cause ESR elevation, hence it's not specific for antecedent streptococcal infection. *Low C3 levels* - **Low C3 levels** are typically associated with complement consumption in diseases like systemic lupus erythematosus or post-streptococcal glomerulonephritis, not directly with ARF. - While post-streptococcal glomerulonephritis can follow a GAS infection, ARF does not primarily involve significant C3 depression as a diagnostic feature. *CRP* - **C-reactive protein (CRP)** is another non-specific acute-phase reactant that is elevated during inflammation, including ARF [2]. - Like ESR, elevated CRP indicates inflammation but does not specifically confirm an antecedent **Group A streptococcal infection**.

Question 895: Most common cause of UTI in young females is?

A. Klebsiella
B. Proteus
C. Staph saprophyticus
D. E. coli (Correct Answer)

Explanation: ***E. coli*** - **Uropathogenic *E. coli*** (*UPEC*) is the most prevalent bacterium responsible for uncomplicated UTIs in otherwise healthy young women. - Its virulence factors, such as **P-fimbriae** (adhesins), allow it to attach to uroepithelial cells and colonize the urinary tract effectively. *Klebsiella* - While *Klebsiella pneumoniae*: can cause UTIs, it is more commonly associated with **hospital-acquired infections** or UTIs in patients with **comorbidities** or instrumentation. - It ranks significantly lower than *E. coli* as a cause of community-acquired UTIs in young females. *Proteus* - *Proteus mirabilis* is known for causing UTIs, especially those associated with **struvite kidney stones** due to its **urease activity**. - However, its incidence as a cause of UTI in young females is much less frequent compared to *E. coli*. *Staph saprophyticus* - **Staphylococcus saprophyticus** is a common cause of UTIs in young, sexually active women, accounting for a significant percentage [1]. - While it is a notable cause, **it is still less common than *E. coli***, which is overwhelmingly the leading pathogen in this demographic.

Question 896: All are major criteria for AIDS except -

A. 10% weight loss
B. Cough for 1 month (Correct Answer)
C. Diarrhoea for 1 month
D. Fever for 1 month

Explanation: *Cough for 1 month* - While chronic cough can occur in AIDS due to opportunistic infections like **Pneumocystis pneumonia** or **tuberculosis**, a cough lasting one month alone is not a primary WHO major criterion for AIDS diagnosis [3]. - The major criteria focus more on significant systemic symptoms like **weight loss**, **chronic fever**, and **chronic diarrhea** [1]. ***10% weight loss*** - **Unexplained weight loss** is a key indicator of **wasting syndrome** which is a major criterion for AIDS, reflecting severe immune compromise and disease progression [1]. - This significant weight loss is often accompanied by other debilitating symptoms. *Diarrhoea for 1 month* - **Chronic diarrhea** (lasting one month or more) is a major criterion for AIDS, often caused by **opportunistic infections** of the gastrointestinal tract like *Cryptosporidium* or *Isospora* [1], [2]. - It signifies severe immune dysfunction and impaired nutrient absorption. *Fever for 1 month* - Persistent **fever** for one month or more, especially if intermittent or constant, is a major criterion for AIDS [1]. - This prolonged fever often signals **ongoing opportunistic infections** or advanced viral disease.

Question 897: Renal involvement is seen in which of the following infections?

A. Cytomegalovirus
B. HBV
C. HIV
D. All of the options (Correct Answer)

Explanation: ***All of the options*** - All three viruses—**Cytomegalovirus (CMV)**, **Hepatitis B virus (HBV)**, and **Human Immunodeficiency Virus (HIV)**—are known to cause significant renal complications. - Renal involvement can manifest as various glomerular diseases (e.g., **glomerulonephritis**, **focal segmental glomerulosclerosis**) or tubulointerstitial nephritis, depending on the specific viral infection and host factors. *Cytomegalovirus* - **CMV** can cause direct renal damage, particularly in **immunocompromised individuals**, leading to interstitial nephritis or glomerulopathy. - It may also contribute to **allograft dysfunction** in kidney transplant recipients through direct viral effects or immune-mediated injury. *HBV* - **HBV infection** is strongly associated with immune complex-mediated renal diseases, most notably **membranous nephropathy** and **membranoproliferative glomerulonephritis**. - These renal manifestations are often driven by the deposition of **HBV antigens** and antibodies in the glomeruli. *HIV* - **HIV-associated nephropathy (HIVAN)** is a classic cause of renal disease in HIV-infected individuals, characterized by collapsing focal segmental glomerulosclerosis. - Other renal pathologies seen in HIV include **immune complex glomerulonephritis**, **thrombotic microangiopathy**, and various forms of **acute kidney injury** related to opportunistic infections or antiretroviral therapy.

Question 898: In diagnosis of AIDS, criteria include the following except -

A. CD8<500 (Correct Answer)
B. CD4<200
C. Presence of any of the opportunistic infections tuberculosis, pneumocystis carinii, cytomegalovirus
D. CD4 : CD 8 =1

Explanation: ***CD8<500*** - While **CD8+ T cells** are involved in the immune response to HIV, their absolute count is not a primary criterion for diagnosing or staging **AIDS**. - **AIDS** diagnosis is primarily based on **CD4+ T cell counts** and the presence of **AIDS-defining opportunistic infections** [1]. *CD4<200* - A **CD4+ T cell count** below **200 cells/µL** is a key diagnostic criterion for **AIDS**, indicating severe immunosuppression [1]. - This threshold signifies a significantly compromised immune system, making the individual highly susceptible to opportunistic infections. *Presence of any of the opportunistic infections tuberculosis, pneumocystis carinii, cytomegalovirus* - The occurrence of **AIDS-defining opportunistic infections** like **tuberculosis**, **Pneumocystis jirovecii pneumonia**, or **cytomegalovirus retinitis** in an HIV-positive individual confirms an **AIDS diagnosis**, regardless of the CD4 count [1]. - These infections typically manifest when the immune system is severely weakened. *CD4 : CD 8 =1* - A **CD4:CD8 ratio of 1** (or any specific ratio) is not a direct criterion for diagnosing **AIDS**. - In HIV infection, the **CD4:CD8 ratio typically inverts** (becomes less than 1) as CD4 cells decline, but this ratio alone is not a defining characteristic for AIDS.

Question 899: Mycobacterium tuberculosis having resistance to rifampicin, isoniazid, and pyrazinamide is described as -

A. Drug resistant tuberculosis
B. Extremely drug resistant tuberculosis
C. Multi drug resistant tuberculosis (Correct Answer)
D. None of the options

Explanation: ***Multi drug resistant tuberculosis*** - This classification specifically refers to *Mycobacterium tuberculosis* resistant to at least **rifampicin** and **isoniazid**, which are the two most potent first-line anti-TB drugs. - While resistance to **pyrazinamide** is also present in this case, the definition of multidrug-resistant tuberculosis (MDR-TB) primarily hinges on resistance to these two core drugs [1]. *Drug resistant tuberculosis* - This is a broad term that can apply to any resistance to one or more anti-TB drugs, but it is not specific enough for resistance to these crucial first-line agents [1]. - It does not convey the clinical and public health implications of resistance to both rifampicin and isoniazid. *Extremely drug resistant tuberculosis* - **Extensively drug-resistant tuberculosis (XDR-TB)** is defined as MDR-TB (resistance to rifampicin and isoniazid) plus resistance to any **fluoroquinolone** and at least one of the three injectable second-line drugs (amikacin, kanamycin, or capreomycin). - The given resistance pattern does not include fluoroquinolones or injectable second-line drugs. *None of the options* - This option is incorrect because the resistance pattern described perfectly fits the definition of multidrug-resistant tuberculosis.

Question 900: Ghon's focus with hilar lymphadenopathy is known as -

A. Borderline Tuberculoid Leprosy
B. Lepromatous Leprosy (LL)
C. Tuberculoid Leprosy (TL) (Correct Answer)
D. Indeterminate Leprosy

Explanation: ***Tuberculoid Leprosy (TL)*** - This question describes a finding related to **tuberculosis**, not leprosy. **Ghon's focus** and **hilar lymphadenopathy** are classic signs of primary tuberculosis infection [1]. - While this option is incorrect in the context of the question's premise (it discusses tuberculosis, not leprosy), among the leprosy types provided, none directly relate to the described imaging findings [2]. Assuming a misinterpretation and seeking the correct leprosy definition. *Borderline Tuberculoid Leprosy* - This form of leprosy lies between tuberculoid and borderline lepromatous leprosy, characterized by a few **skin lesions** and moderate nerve involvement [2]. - It does not involve **Ghon's focus** or **hilar lymphadenopathy**, which are features of tuberculosis [1]. *Lepromatous Leprosy (LL)* - This is a severe, multi-bacillary form of leprosy with diffuse infiltration of skin, multiple **nodules**, and widespread **nerve damage** [2]. - It has no association with **Ghon's focus** or **hilar lymphadenopathy**. *Indeterminate Leprosy* - This is the earliest form of leprosy, characterized by a single patch or a few poorly defined **skin lesions**, with minimal or no nerve involvement [2]. - It does not present with **Ghon's focus** or **hilar lymphadenopathy**.

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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