Infectious Diseases Practice Questions

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

ASO. ***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**.

Q: All are major criteria for AIDS except -

Cough for 1 month. *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.

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

All of the options. ***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.

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

CD8<500. ***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.

Q: WHO stage IV HIV includes all, except:

Oral thrush. ***Oral thrush*** - While common in HIV, **oral candidiasis (thrush)** is typically classified as a **WHO clinical stage I or II** condition, indicating less severe immunosuppression. - It does not signify the profound immune compromise characteristic of stage IV disease. *HIV wasting syndrome* - **HIV wasting syndrome** is explicitly listed as a **major clinical condition** in WHO clinical stage IV HIV infection. - It is defined by **involuntary weight loss** of more than 10% of baseline body weight, accompanied by fever or diarrhea for at least 30 days, or unexplained chronic weakness. *Pneumocystis jirovecii* - **Pneumocystis jirovecii pneumonia (PCP)** is a classic **opportunistic infection (OI)** that classifies HIV infection as **WHO clinical stage IV**. - Its presence indicates severe immune suppression and often signifies advanced disease. *Toxoplasmosis* - **Toxoplasmosis of the central nervous system (CNS)**, particularly cerebral toxoplasmosis, is a defining **WHO clinical stage IV** opportunistic infection in HIV. - It reflects severe immune compromise, making the patient susceptible to reactivation of latent *Toxoplasma gondii* infection.

Q: Complications of tubercular meningitis include all except

Cortical venous thrombosis. ***Cortical venous thrombosis*** - While TB meningitis can cause vascular complications, **isolated cortical venous thrombosis** is a rare and atypical complication. - The inflammatory exudate in TB meningitis typically affects arteries and basal cisterns, leading to problems like arteritis and communicating or obstructive hydrocephalus [1]. *Hydrocephalus* - This is a common complication due to the inflammatory exudate in the **basal cisterns**, which obstructs the flow of cerebrospinal fluid (CSF) [2]. - It can be either **communicating** (impaired absorption) or **non-communicating** (obstructive due to blockage) [2]. *Cerebral Artery Thrombosis* - The **inflammatory exudate** surrounding basal cisterns in TB meningitis can lead to vasculitis and thrombosis of nearby arteries, especially the large cerebral arteries. - This can result in **ischemic strokes** and focal neurological deficits [3]. *Cranial Nerve Palsy* - The inflamed meninges and exudate can directly compress or damage **cranial nerves** as they exit the brainstem and travel through the basal cisterns. - Cranial nerves III, IV, VI, VII, and VIII are particularly susceptible to this complication.

Q: Dengue haemorrhagic fever is diagnosed by-

Acute onset of high fever, positive tourniquet test, bleeding gum and platelet count < 100,000/µL. Dengue haemorrhagic fever is diagnosed by- ***Acute onset of high fever, positive tourniquet test, bleeding gum, and platelet count < 100,000/µL*** - **Dengue hemorrhagic fever (DHF)** is characterized by **acute high fever**, evidence of **plasma leakage**, and **hemorrhagic manifestations** such as **bleeding gums**, along with significant **thrombocytopenia** (platelet count 150,000/µL* - While **acute high fever**, **positive tourniquet test**, **epistaxis**, or **melena** can be present in DHF, a **platelet count > 150,000/µL** is contrary to the diagnostic criteria for DHF. - DHF requires significant **thrombocytopenia** (platelet count 200,000/µL* - The presence of **acute high fever**, **petechiae**, and **epistaxis** are consistent with DHF symptoms, indicating bleeding tendencies [1]. - However, a **platelet count > 200,000/µL** contradicts the diagnostic criteria for DHF, which mandates **thrombocytopenia** (<100,000/µL). *Acute onset of high fever (2-7 days), hemorrhagic manifestation (e.g., hemoptysis), and platelet count < 150,000/µL* - **Acute high fever** and **hemorrhagic manifestations** like **hemoptysis** (though less common than other forms of bleeding) are features of DHF. - However, while **platelet count < 150,000/µL** indicates thrombocytopenia, the specific diagnostic threshold for DHF is typically **< 100,000/µL**.

Q: CSF examination is most commonly indicated in:

Suspected bacterial meningitis. ***Suspected bacterial meningitis*** - A **lumbar puncture** to obtain **CSF for analysis** is crucial for diagnosing **bacterial meningitis**, as it provides definitive information on cell count, glucose, protein, and presence of bacteria [1]. - Early and accurate diagnosis is critical for initiating specific **antibiotic therapy** and preventing severe neurological sequelae or death. *Suspected viral encephalitis* - While CSF analysis is helpful in **viral encephalitis** to look for **lymphocytic pleocytosis**, elevated protein, and normal glucose, it is not the most common or primary indication compared to suspected bacterial meningitis which demands urgent and specific treatment decisions [2]. - **Neuroimaging (MRI)** is often more informative initially in viral encephalitis to look for parenchymal involvement. *Suspected subarachnoid hemorrhage* - In suspected **subarachnoid hemorrhage (SAH)**, a **CT scan of the head** is the initial imaging modality of choice. - Lumbar puncture is typically performed only if the **CT scan is negative** but clinical suspicion remains high, to look for **xanthochromia**, which indicates old blood products [4]. *Suspected tuberculous meningitis* - Although **CSF analysis** is essential for diagnosing **tuberculous meningitis**, specifically looking for **lymphocytic pleocytosis**, low glucose, and high protein, the diagnostic process involves more specialized tests like **CSF culture for acid-fast bacilli** (which can take weeks) or **PCR** [3]. - Its incidence is lower than bacterial meningitis in many regions, making it a less common indication for urgent CSF sampling in the general population compared to acute bacterial infection [5].

Q: Best initial screening test to diagnose HIV infection

ELISA. ***ELISA*** - **ELISA** (Enzyme-linked immunosorbent assay) is the most widely used and recommended initial screening test for HIV due to its high **sensitivity** and relative affordability [1]. - It detects **HIV antibodies** and/or **p24 antigen**, allowing for early detection of infection [1], [2]. *Complement fixation test* - The complement fixation test is a serological method used to detect antibodies or antigens, but it is **not commonly used** for HIV screening. - It has **lower sensitivity** and **specificity** for HIV compared to modern assays like ELISA. *Western blot* - The **Western blot** is a highly specific test used as a **confirmatory test** for HIV, not an initial screening test due to its complexity and cost [1], [2]. - It detects specific HIV proteins, used to confirm a positive ELISA result [2]. *RIA* - **Radioimmunoassay (RIA)** is a sensitive technique used to measure antigen or antibody concentrations, but it is **not the primary screening test** for HIV. - RIA involves **radioactive isotopes**, which pose logistical and safety challenges, making it less practical for routine screening compared to ELISA.

Q: In patients of acquired immunodeficiency syndrome, the commonest cause of space occupying lesion in brain is -

Toxoplasmosis. ***Toxoplasmosis*** - **Toxoplasma gondii** is the most common opportunistic central nervous system infection in patients with AIDS, leading to cerebral toxoplasmosis [1]. - It typically presents as a **space-occupying lesion** or multiple ring-enhancing lesions on imaging, associated with focal neurological deficits, seizures, and altered mental status [1]. *Cryptococcosis* - While common in AIDS patients, **Cryptococcus neoformans** primarily causes **meningitis** (meningoencephalitis), not typically a solitary space-occupying lesion. - Brain parenchymal involvement can occur but is usually multifocal or in the form of cryptococcomas, which are less common than toxoplasmosis. *Non Hodgkin's lymphoma* - **Primary central nervous system lymphoma (PCNSL)** is a significant cause of space-occupying lesions in AIDS patients, but it is **less common than toxoplasmosis** [1]. - It often presents as a solitary lesion, deep-seated, or periventricular, and may be difficult to distinguish from toxoplasmosis without biopsy [1]. *Cytomegalovirus infection* - **CMV** can cause various neurological complications in AIDS patients, including **ventriculoencephalitis**, myelitis, and polyradiculopathy [2]. - While it can cause periventricular enhancement on imaging, it typically causes **diffuse encephalitis** or retinitis, rather than discrete space-occupying lesions [2].

Question 1

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

Accepted Answer

ASO

Answer

ESR elevation

Answer

Low C3 levels

Answer

CRP

Question 2

All are major criteria for AIDS except -

Accepted Answer

Cough for 1 month

Answer

10% weight loss

Answer

Diarrhoea for 1 month

Answer

Fever for 1 month

Question 3

Renal involvement is seen in which of the following infections?

Accepted Answer

All of the options

Answer

Cytomegalovirus

Answer

HBV

Answer

HIV

Question 4

In diagnosis of AIDS, criteria include the following except -

Accepted Answer

CD8<500

Answer

CD4<200

Answer

Presence of any of the opportunistic infections tuberculosis, pneumocystis carinii, cytomegalovirus

Answer

CD4 : CD 8 =1

Question 5

WHO stage IV HIV includes all, except:

Accepted Answer

Oral thrush

Answer

HIV wasting syndrome

Answer

Pneumocystis jirovecii

Answer

Toxoplasmosis

Question 6

Complications of tubercular meningitis include all except

Accepted Answer

Cortical venous thrombosis

Answer

Hydrocephalus

Answer

Cerebral Artery Thrombosis

Answer

Cranial Nerve Palsy

Question 7

Dengue haemorrhagic fever is diagnosed by-

Accepted Answer

Acute onset of high fever, positive tourniquet test, bleeding gum and platelet count < 100,000/µL

Answer

Acute onset of high fever, positive tourniquet test, epistaxis or melena, and platelet count > 150,000/µL

Answer

Acute onset of high fever, presence of petechiae, epistaxis and platelet count > 200,000/µL

Answer

Acute onset of high fever (2-7 days), hemorrhagic manifestation (e.g., hemoptysis), and platelet count < 150,000/µL

Question 8

CSF examination is most commonly indicated in:

Accepted Answer

Suspected bacterial meningitis

Answer

Suspected viral encephalitis

Answer

Suspected subarachnoid hemorrhage

Answer

Suspected tuberculous meningitis

Question 9

Best initial screening test to diagnose HIV infection

Accepted Answer

ELISA

Answer

Complement fixation test

Answer

Western blot

Answer

RIA

Question 10

In patients of acquired immunodeficiency syndrome, the commonest cause of space occupying lesion in brain is -

Accepted Answer

Toxoplasmosis

Answer

Cryptoccosis

Answer

Non Hodgkin's lymphoma

Answer

Cytomegalovirus infection

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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