Infectious Diseases Practice Questions

Q: A 38-year-old male presents with a one-week history of fever, headache, retro-orbital pain, and myalgia. Skin examination reveals multiple purpura and petechiae on the left shoulder, trunk, and legs. Similar cases have been reported linked to increased incidence of mosquito breeding. What is the most common neurological complication associated with this condition?

Encephalopathy. ***Encephalopathy***- **Encephalopathy** is the most frequent neurological complication in severe **Dengue fever**, often resulting from systemic factors like **shock**, **hypoxia**, **hepatic dysfunction**, or **hyponatremia** rather than direct viral invasion [1].- The presented symptoms (fever, retro-orbital pain, myalgia, hemorrhagic signs/purpura) are classic for severe Dengue, where multorgan failure and systemic derangements frequently lead to altered consciousness [1].*Guillain-Barré Syndrome*- **GBS** is a **post-infectious** demyelinating condition that typically manifests after recovery from the acute viral illness, presenting as progressive, ascending paralysis.- While Dengue is a recognized trigger for GBS, it is much less common than acute encephalopathy occurring during the febrile or critical phase of the illness.*Stroke*- **Stroke** (ischemic or hemorrhagic) can occur in severe dengue due to complications like **vasculitis**, **coagulopathy**, or profound **thrombocytopenia**, leading to focal neurological deficits.- Although the hemorrhagic signs (purpura/petechiae) indicate a risk for bleeding complications, stroke is generally less common than systemic **encephalopathy** in the overall spectrum of dengue neuro-complications [1].*Encephalitis*- **Encephalitis** refers to inflammation of the brain caused by **direct viral invasion** of the central nervous system by the Dengue virus.- While possible, primary dengue encephalitis due to neurotropism is considered a relatively rare neurological manifestation compared to secondary **dengue-associated encephalopathy** [1].

Q: A patient is diagnosed with Cryptococcal meningitis. What is the treatment?

Flucytosine + L.Amp. ***Correct: Flucytosine + L.Amp (Liposomal Amphotericin B)*** - This is the **standard induction therapy** for Cryptococcal meningitis as per WHO and CDC guidelines [1] - **Combination therapy** is superior to monotherapy, reducing mortality and improving outcomes [1] - The induction phase lasts **2 weeks**, followed by consolidation with fluconazole [1] - Liposomal Amphotericin B has **better CNS penetration** and fewer nephrotoxic effects compared to conventional Amphotericin B - Flucytosine enhances fungicidal activity and reduces the risk of resistance [1] *Incorrect: L.Amp alone* - Monotherapy with Amphotericin B is **less effective** than combination therapy [1] - Higher rates of treatment failure and relapse when used alone - Should always be combined with flucytosine when available [1] *Incorrect: Fluconazole alone* - Fluconazole is used in **consolidation phase** (after induction) and maintenance therapy - **Not recommended for induction** due to its fungistatic (not fungicidal) action - Slower CSF sterilization compared to combination therapy *Incorrect: Flucytosine alone* - **Never used as monotherapy** due to rapid development of resistance - Must always be combined with Amphotericin B or Azoles - Has good CSF penetration but inadequate as sole agent

Q: Which of the following is the management of a HIV positive patient with multiple dog bites?

Rabies vaccine + Immunoglobulin + Wound management. ***Rabies vaccine + Immunoglobulin + Wound management***- **Category III exposure** (multiple/deep transmural bites) mandates both **Passive Immunization** (Human Rabies Immune Globulin - **HRIG**) and **Active Immunization** (**Rabies Vaccine**) for immediate and long-term protection [1].- Given the patient's **HIV-positive status**, they are considered **immunocompromised**; therefore, the highest level of post-exposure prophylaxis (PEP) is required to ensure adequate viral neutralization and immune response.*Rabies vaccine + wound management*- This regimen is inadequate for **Category III exposure** because it omits **Rabies Immunoglobulin (RIG)**, which provides immediate, neutralizing antibodies before the vaccine takes effect [1].- Omitting RIG is particularly dangerous in an **immunocompromised patient** as the onset of antibody production from the vaccine may be delayed or suboptimal.*Immunoglobulin only*- **Rabies Immunoglobulin (RIG)** provides vital passive immunity but its effects are short-lived, offering only temporary protection.- Effective rabies prevention requires the simultaneous administration of the **active vaccine** series to stimulate sustained, long-term protective antibody production [1].*Wound management*- While essential for reducing local bacterial infections and viral load, **wound management alone** is never sufficient for managing **Category III rabies exposure**.- This option neglects both the immediate (RIG) and subsequent (Vaccine) specific measures required to prevent the invariably fatal neurological disease caused by the **Rabies virus**.

Q: A patient presents with fever, neck rigidity, headache, vomiting, and petechial rashes on the lower limbs. What is the most likely causative organism?

Neisseria meningitidis. ***Neisseria meningitidis***- This gram-negative diplococcus is the most likely causative agent as it classically causes **meningococcal meningitis** combined with **meningococcemia**, which highly correlates with the presence of **petechial or purpuric rashes** on the skin.- The rash results from **endotoxin** (lipooligosaccharide) damage to the blood vessel walls, leading to **vasculitis** and hemorrhage, often progressing to severe complications like the **Waterhouse-Friderichsen syndrome**.*Clostridium perfringens*- This organism is primarily known for causing **gas gangrene** (myonecrosis) and tissue necrosis, often following severe trauma or surgery.- It is not a common cause of primary community-acquired bacterial meningitis, and its clinical presentation focuses on localized **soft tissue infection** rather than systemic meningoencephalitis.*Cryptococcus neoformans*- This is a **fungal pathogen** that causes meningitis, usually in patients with **severe immunosuppression** (e.g., uncontrolled HIV infection).- Although it causes fever and signs of meningeal irritation, the presentation is typically subacute or chronic, and a hemorrhagic rash is not a standard clinical feature.*Clostridium difficile*- This bacterium is the causative agent of **antibiotic-associated diarrhea** and **pseudomembranous colitis**.- Its effects are localized almost exclusively to the colon, and it does not cause acute bacterial meningitis with systemic rash.

Q: A farmer presents with fever and subconjunctival hemorrhage. The microscopic agglutination test is found to be positive. What is the diagnosis?

Leptospira. ***Leptospira***- The clinical presentation of fever in a patient with an occupation involving exposure to animal habitats (farmer), coupled with the classic finding of **subconjunctival hemorrhage** (conjunctival suffusion), highly suggests **Leptospirosis** (Weil's disease) [1]. - The **Microscopic Agglutination Test (MAT)** is the gold standard serological test for the diagnosis of **Leptospirosis**, supporting this etiology [1]. *Brucella* - *Brucella* causes **Brucellosis** (Undulant Fever), characterized primarily by cyclical undulating fevers, night sweats, and localized infection (e.g., osteomyelitis or epididymitis), not typically subconjunctival hemorrhage. - Diagnosis usually involves blood culture or the Standard Tube Agglutination Test (SAT), not MAT. *E coli* - *E. coli* is a common cause of GI infections, UTIs, and sepsis; systemic *E. coli* disease does not typically manifest with the specific finding of subconjunctival hemorrhage. - MAT is not used for the diagnosis of *E. coli* infections, which are confirmed primarily through culture. *Staph aureus* - *S. aureus* can cause a wide range of infections (skin infections, endocarditis, sepsis) but is not associated with the specific syndrome presenting here (farmer, subconjunctival hemorrhage). - Diagnosis relies on culture, not serological tests like MAT, which is specific for spirochetes.

Q: A patient is positive for HBsAg and anti-HBc IgM. What is the most likely diagnosis?

Acute hepatitis. ***Acute hepatitis***- The simultaneous presence of **HBsAg** (Hepatitis B surface antigen) indicates active infection [1], paired with **anti-HBc IgM** (Immunoglobulin M against the core antigen) [2].- **Anti-HBc IgM** is the serological hallmark of a recent or **acute** Hepatitis B infection, typically detectable for up to 6 months after symptom onset [1].*Chronic hepatitis*- Chronic infection is defined by the persistence of **HBsAg** for **more than six months** [1].- The predominant core antibody present in chronic infection is **anti-HBc IgG**, whereas Anti-HBc IgM becomes undetectable [1].*Recovery phase*- The recovery phase is marked by the presence of **anti-HBs** (Hepatitis B surface antibody), indicating clearance of the virus and protective immunity [1].- During recovery, **HBsAg** is negative, and **anti-HBc IgM** is absent, leaving only **anti-HBc IgG** and anti-HBs [1].*Vaccination*- Successful vaccination only produces immunity against the surface antigen, resulting solely in the presence of **anti-HBs** [1].- Both **HBsAg** and **anti-HBc** (IgM or IgG) are universally negative following vaccination [1].

Q: A patient admitted with fever and nuchal rigidity. CSF analysis shows decreased glucose and increased protein and neutrophils. Which is the MOST IMPORTANT antibiotic for initial empirical treatment?

Ceftriaxone. Ceftriaxone - Ceftriaxone, a third-generation cephalosporin, is the most essential component of empirical treatment for bacterial meningitis due to its excellent CSF penetration and broad coverage [1]. - It effectively covers the most common bacterial causes of community-acquired meningitis: Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae [1]. - Note: Current guidelines recommend Ceftriaxone + Vancomycin as the optimal empirical regimen to cover penicillin-resistant S. pneumoniae (PRSP), but Ceftriaxone remains the primary/essential antibiotic in this combination [1]. Vancomycin - Vancomycin is critical for covering penicillin-resistant S. pneumoniae (PRSP) and is typically used in combination with Ceftriaxone in the empirical regimen. - It is not used as monotherapy due to poor CSF penetration and incomplete coverage of other common pathogens like N. meningitidis. Penicillin - Penicillin is no longer recommended for empirical treatment due to high prevalence of penicillin-resistant S. pneumoniae (PRSP) globally. - While effective against sensitive N. meningitidis, the need for broader coverage necessitates third-generation cephalosporins. Ampicillin - Ampicillin is added to cover Listeria monocytogenes in specific high-risk groups: patients >50 years, immunocompromised, pregnant women, or neonates. - It is ineffective as monotherapy for routine bacterial meningitis and lacks coverage for resistant strains of common pathogens.

Q: A TB patient with HIV begins ART and experiences deterioration in health after 2 months. What is the likely cause?

Immunological changes in the body. ***Immunological changes in the body*** - The patient's deterioration 2 months after initiating ART is highly suggestive of **Immune Reconstitution Inflammatory Syndrome (IRIS)** [1]. - IRIS occurs when the partially restored immune system mounts an intense, often paradoxical, inflammatory response against high existing **Mycobacterium tuberculosis** antigen loads [1]. *Development of drug resistance to TB drugs* - If resistance developed, the patient would typically fail to improve or experience gradual worsening, consistent with inadequate **TB coverage**, not an acute, paradoxical inflammatory reaction. - Worsening due to drug resistance is usually not temporally linked to the start of ART and would require specific **drug sensitivity testing (DST)** for confirmation [1]. *Drug-drug interactions between TB and ART medications* - Significant drug-drug interactions (e.g., between **rifampicin** and certain ART drugs) typically lead to systemic toxicity or subtherapeutic drug levels, manifesting as virologic failure or liver injury, not acute inflammatory worsening of the underlying TB. - Interactions lead to either rapid ART failure or toxicity, but not the specific clinical picture of **paradoxical TB-IRIS** where infectious signs temporarily worsen. *Development of drug resistance to ART* - Resistance to ART typically manifests as a failure of the **HIV viral load** to decrease or subsequent increase, leading to chronic progression of AIDS, not acute deterioration via inflammation of latent or subclinical TB [1]. - Developing drug resistance often requires prolonged exposure to a suboptimal regimen and usually takes longer than 2 months to cause significant clinical decline via **virologic failure**.

Q: Which of the following microorganisms is likely responsible for causing bilateral infiltrates in an HIV-positive patient?

Pneumocystis Jirovecii. ***Pneumocystis Jirovecii***- **Pneumocystis Pneumonia (PCP)** is the most common AIDS-defining infection affecting the lungs, typically presenting with **diffuse, bilateral, perihilar interstitial infiltrates** in HIV patients [1]. - This infection is strongly associated with a **CD4 cell count below 200 cells/mm³** and often manifests clinically with gradual onset of dyspnea, fever, and a non-productive cough [1].*Cryptococcus*- Although *Cryptococcus neoformans* is a common opportunistic infection in HIV, it predominantly causes **meningitis** or **meningoencephalitis**. - Pulmonary involvement usually presents as **nodules** or localized consolidations, not the classic diffuse bilateral interstitial pattern seen with PCP.*Histoplasmosis*- *Histoplasma capsulatum* is an endemic pathogen (e.g., Ohio and Mississippi River Valleys) that typically causes **disseminated disease** in advanced HIV. - While pulmonary infection may occur, it often presents with **hilar/mediastinal lymphadenopathy** [2] or a miliary pattern, rather than isolated bilateral interstitial infiltrates.*Aspergillus*- **Invasive Aspergillosis** generally occurs in patients with profound and prolonged **neutropenia** (e.g., following chemotherapy or transplantation), which is less common in typical AIDS patients with low CD4 counts. - Pulmonary findings usually involve localized **cavities** or **nodules with a halo sign** (angioinvasive disease), contrasting with the diffuse bilateral infiltrates of PCP.

Q: A 70-year-old patient with a smoking history presents with high-grade fever, cough, confusion, and diarrhea. Chest X-ray shows bilateral infiltrates in bilateral lower lung fields. On sputum gram stain, no organisms were detected. Laboratory results reveal Na: 126mEq/L, AST:62, ALT:56, RBS:112 mg/dl, serum bilirubin of 0.8mg%, and a positive HIV test. Which of the following organisms is responsible?

Legionella. ***Legionella***- This clinical picture, characterized by **high fever**, **atypical pneumonia** (bilateral infiltrates), and systemic symptoms including **confusion** (CNS involvement), **diarrhea** (GI involvement), **hyponatremia** and mildly elevated **LFTs**, is highly suggestive of **Legionella pneumophila** (Legionnaires' disease) [1].- *Legionella* is an **atypical bacterium** that requires specialized culture media and therefore typically results in a Gram stain showing **no organisms detected** through standard methods [1].*Streptococcus*- *Streptococcus pneumoniae* (the most common cause of typical community-acquired pneumonia) typically presents with an abrupt onset, pleurisy, and a consolidation pattern (**lobar pneumonia**) on CXR, differentiating it from this diffuse, atypical presentation.- It is a readily detectable **Gram-positive diplococcus** on sputum Gram stain, which contrasts with the microbiological report of no organisms seen [1].*Pneumocystis jeroveci*- While highly relevant in HIV-positive individuals, **Pneumocystis pneumonia (PJP)** typically presents with subacute onset, severe **hypoxemia**, and diffuse **interstitial infiltrates**, not typically associated with prominent hyponatremia or severe diarrhea [2].- PJP is diagnosed via special staining (e.g., silver stain) on induced sputum or bronchoalveolar lavage, and it does not usually cause the multisystem failure (hyponatremia and transaminitis) characteristic of Legionnaires' disease [2].*Klebsiella*- **Klebsiella pneumoniae** typically causes destruction and necrosis leading to classic **lobar pneumonia** (often in the upper lobes), classically associated with **currant jelly sputum** in immunocompromised individuals, especially alcoholics.- *Klebsiella* is a large encapsulated **Gram-negative rod** that would be easily visible and identifiable on a standard sputum Gram stain.

Question 1

A 38-year-old male presents with a one-week history of fever, headache, retro-orbital pain, and myalgia. Skin examination reveals multiple purpura and petechiae on the left shoulder, trunk, and legs. Similar cases have been reported linked to increased incidence of mosquito breeding. What is the most common neurological complication associated with this condition?

Accepted Answer

Encephalopathy

Answer

Stroke

Answer

Encephalitis

Answer

Guillain-Barré Syndrome

Question 2

A patient is diagnosed with Cryptococcal meningitis. What is the treatment?

Accepted Answer

Flucytosine + L.Amp

Answer

L.Amp

Answer

Fluconazole

Answer

Flucytosine

Question 3

Which of the following is the management of a HIV positive patient with multiple dog bites?

Accepted Answer

Rabies vaccine + Immunoglobulin + Wound management

Answer

Immunoglobulin only

Answer

Wound management

Answer

Rabies vaccine + wound management

Question 4

A patient presents with fever, neck rigidity, headache, vomiting, and petechial rashes on the lower limbs. What is the most likely causative organism?

Accepted Answer

Neisseria meningitidis

Answer

Cryptococcus neoformans

Answer

Clostridium difficile

Answer

Clostridium perfringens

Question 5

A farmer presents with fever and subconjunctival hemorrhage. The microscopic agglutination test is found to be positive. What is the diagnosis?

Accepted Answer

Leptospira

Answer

Brucella

Answer

E coli

Answer

Staph aureus

Question 6

A patient is positive for HBsAg and anti-HBc IgM. What is the most likely diagnosis?

Accepted Answer

Acute hepatitis

Answer

Recovery phase

Answer

Vaccination

Answer

Chronic hepatitis

Question 7

A patient admitted with fever and nuchal rigidity. CSF analysis shows decreased glucose and increased protein and neutrophils. Which is the MOST IMPORTANT antibiotic for initial empirical treatment?

Accepted Answer

Ceftriaxone

Answer

Vancomycin

Answer

Penicillin

Answer

Ampicillin

Question 8

A TB patient with HIV begins ART and experiences deterioration in health after 2 months. What is the likely cause?

Accepted Answer

Immunological changes in the body

Answer

Development of drug resistance to ART

Answer

Development of drug resistance to TB drugs

Answer

Drug-drug interactions between TB and ART medications

Question 9

Which of the following microorganisms is likely responsible for causing bilateral infiltrates in an HIV-positive patient?

Accepted Answer

Pneumocystis Jirovecii

Answer

Histoplasma

Answer

Aspergillus

Answer

Cryptococcus

Question 10

A 70-year-old patient with a smoking history presents with high-grade fever, cough, confusion, and diarrhea. Chest X-ray shows bilateral infiltrates in bilateral lower lung fields. On sputum gram stain, no organisms were detected. Laboratory results reveal Na: 126mEq/L, AST:62, ALT:56, RBS:112 mg/dl, serum bilirubin of 0.8mg%, and a positive HIV test. Which of the following organisms is responsible?

Accepted Answer

Legionella

Answer

Klebsiella

Answer

Streptococcus

Answer

Pneumocystis jeroveci

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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