Infectious Diseases Practice Questions

Q: A 45-year-old female presents with abdominal pain, jaundice, and fever. An abdominal CT scan reveals multiple liver abscesses, and aspiration yields anchovy paste-like pus. What is the most likely etiological agent responsible for these findings?

Entamoeba histolytica. ***Entamoeba histolytica*** - The combination of **abdominal pain**, **jaundice**, **fever**, and **multiple liver abscesses** with **anchovy paste-like pus** is highly characteristic of an **amebic liver abscess** caused by *Entamoeba histolytica* [1]. - This parasite is acquired through the **fecal-oral route** and can invade the intestinal wall, leading to extraintestinal dissemination, most commonly to the liver [1]. *Echinococcus granulosus* - This pathogen causes **hydatid cysts**, which are typically **single**, large cysts with an **acellular fluid** rather than a purulent or "anchovy paste-like" consistency [2]. - While it can cause abdominal pain and jaundice, the pus description is not consistent with **hydatid disease** [2]. *Staphylococcus aureus* - **Pyogenic liver abscesses** caused by *Staphylococcus aureus* typically present with **fever** and **abdominal pain** but commonly involve **multiple smaller abscesses** and the pus is typically **creamy** and foul-smelling, not resembling "anchovy paste." - These are often associated with a primary source of infection, such as **bacteremia**. *Klebsiella pneumoniae* - **Klebsiella pneumoniae** is a common cause of **pyogenic liver abscesses**, particularly in patients with **diabetes mellitus**, and can present with fever, abdominal pain, and jaundice [2]. - However, the pus from a *Klebsiella* abscess is typically **thick and purulent** but lacks the distinctive **"anchovy paste" appearance** seen in amebic abscesses.

Q: Which type of hepatitis virus is most likely to progress to chronic hepatitis?

Hepatitis C. ***Hepatitis C*** - **Hepatitis C virus (HCV)** is highly prone to chronic infection, with approximately **75-85% of acutely infected individuals** developing chronic hepatitis [1]. - Chronic HCV infection can lead to **cirrhosis**, **liver failure**, and **hepatocellular carcinoma** over many years [1]. *Hepatitis A* - **Hepatitis A virus (HAV)** typically causes an **acute, self-limiting infection** and does not lead to chronic hepatitis. - It resolves spontaneously, and patients develop ** lifelong immunity** without long-term liver damage. *Hepatitis B* - While Hepatitis B virus (HBV) can cause chronic infection, the progression rate is **highly dependent on age of infection** (e.g., >90% in perinatally infected vs. <5% in adult-acquired). - Overall, a significant proportion of adults with acute HBV **clear the virus spontaneously**, unlike HCV. *Hepatitis E* - **Hepatitis E virus (HEV)** usually causes an **acute infection** that is self-limiting and does not lead to chronic disease in immunocompetent individuals. - Chronic HEV infection can occur in **immunocompromised patients**, but this is less common than chronic HCV.

Q: A patient with acute myelogenous leukemia develops severe neutropenia following chemotherapy. He presents with fever and multiple nodular lung infiltrates. What are the likely pathogens and the preferred empirical therapy?

Fungal pneumonia in neutropenic patient. **Fungal pneumonia in neutropenic patient** - The presence of **fever**, **neutropenia**, and **multiple nodular lung infiltrates** in an acute myelogenous leukemia patient post-chemotherapy is highly suggestive of **invasive fungal infection**, particularly aspergillosis [1]. - **Empirical antifungal therapy**, such as voriconazole or a lipid formulation of amphotericin B, is crucial in this high-risk population given the high mortality associated with delayed treatment [2]. *Gram-positive bacterial pneumonia in immunocompromised patient* - While gram-positive bacteria can cause pneumonia in neutropenic patients, **nodular lung infiltrates** are less typical for common bacterial pneumonias which often present with lobar consolidation. - Bacterial pneumonia might be considered, but the risk of fungal infection is paramount given the clinical scenario, necessitating broader coverage. *Atypical pneumonia in immunocompromised setting* - **Atypical pneumonias** (e.g., *Mycoplasma, Chlamydophila, Legionella*) generally cause interstitial infiltrates, not typically multiple distinct nodules. - While possible, the immune status and radiological findings steer away from atypical bacterial pathogens as the primary concern. *Respiratory infection in immunocompromised host* - This is too broad and does not specify the likely pathogens or preferred therapy to address the critical situation [3]. - The clinical presentation demands a more targeted approach, prioritizing the most dangerous and likely organisms like fungi, which are strongly suggested by the nodular infiltrates in a neutropenic patient [1].

Q: A patient with diabetes presents with a black eschar on the nose and facial swelling. A biopsy shows broad, non-septate hyphal elements with right-angle branching. Assess the likely diagnosis and the urgency of the management required.

Mucormycosis, immediate aggressive treatment. ***Mucormycosis, immediate aggressive treatment*** - The presence of a **black eschar**, **facial swelling** in a diabetic patient, and biopsy findings of **broad, non-septate hyphal elements with right-angle branching** are classic for **mucormycosis** [1]. - This is an **opportunistic fungal infection** that is rapidly progressive and highly fatal, requiring **immediate aggressive treatment** including surgical debridement and antifungal therapy (e.g., amphotericin B) [1]. *Aspergillosis, elective treatment* - **Aspergillosis** typically presents with **septate hyphae with acute angle branching**, which differs from the *non-septate, right-angle branching* seen in the biopsy. - While serious, it does not typically manifest with a **black eschar** as the primary sign of rhino-orbital-cerebral involvement; also, the urgency described for mucormycosis is much higher than for most forms of aspergillosis. *Candidiasis, standard antifungal treatment* - **Candidiasis** usually presents with **pseudohyphae and budding yeasts**; it does not exhibit the *broad, non-septate hyphal elements* described. - While fungal, it rarely causes a **necrotic black eschar** in the absence of severe systemic involvement in immunocompromised patients, and its treatment regimen is generally less urgent and aggressive than for mucormycosis. *Dermatophytosis, topical treatment* - **Dermatophytosis (ringworm)** is a **superficial fungal infection** of the skin, hair, or nails, typically presenting with *erythematous, scaly lesions*. - It would not cause a **black eschar** or facial swelling indicative of deep tissue invasion, nor would the biopsy show *broad, non-septate hyphae* in the manner described.

Q: A patient presents with a bull's-eye rash and flu-like symptoms following a tick bite. What is the most likely diagnosis?

Lyme disease. ***Lyme disease*** - The classic **bull's-eye rash** (erythema migrans) is a hallmark sign of early **Lyme disease**, often accompanied by **flu-like symptoms** after a tick bite [1]. - This presentation is highly indicative of infection with **Borrelia burgdorferi**, transmitted by **Ixodes ticks** [1]. *Rocky Mountain spotted fever* - Characterized by a **maculopapular rash** that typically starts on the **ankles and wrists** and spreads centrally, often becoming **petechial**. - While it follows a tick bite and can present with flu-like symptoms, the rash is not described as a **bull's-eye**. *Ehrlichiosis* - Symptoms include **fever, headache, malaise**, and **muscle aches** after a tick bite [1]. - A rash is less common and, if present, is usually **maculopapular** or **petechial**, not the characteristic bull's-eye. *Anaplasmosis* - Presents with **fever, chills, headache**, and **myalgia** following a tick bite, similar to other tick-borne illnesses. - It does **not typically cause a rash**, distinguishing it from Lyme disease and RMSF.

Q: In a patient with AIDS and a CD4 count of fewer than 50 cells/µL, which of the following opportunistic infections is most likely to occur?

Cryptococcus neoformans. ***Cryptococcus neoformans*** - **Cryptococcal meningitis** is a common and severe opportunistic infection in AIDS patients with **CD4 counts below 50 cells/µL** [1]. - It often presents with **headache**, **fever**, **nuchal rigidity**, and altered mental status. *Candida albicans* - While common in AIDS patients, **oral candidiasis (thrush)** typically occurs at **higher CD4 counts** (e.g., below 200 cells/µL) and is less indicative of a CD4 count below 50 cells/µL compared to cryptococcosis [2]. - Systemic candidiasis is less common than oral or esophageal forms in this setting [1]. *Aspergillus fumigatus* - **Aspergillosis** is typically seen in patients with **severe neutropenia** and profound immunosuppression, often related to hematological malignancies or transplant, rather than solely based on low CD4 count in AIDS. - It is less likely to be the *most likely* opportunistic infection at a CD4 count of fewer than 50 cells/µL in an HIV patient presenting with typical symptoms of opportunistic infection. *Histoplasma capsulatum* - **Disseminated histoplasmosis** can occur in AIDS patients with CD4 counts below 100-150 cells/µL, but it is **geographically localized** to endemic areas (e.g., Ohio and Mississippi River valleys) [3]. - Cryptococcal meningitis is more universally prevalent in AIDS patients with very low CD4 counts, making it a more likely general answer.

Q: A 22-year-old male with a sore throat, fever, and swollen lymph nodes presents with white patches on his tonsils. A rapid antigen detection test is negative. What is the next best step?

Perform a throat culture. ***Perform a throat culture*** - A negative **rapid antigen detection test (RADT)** does not completely rule out **streptococcal pharyngitis**, especially in highly suspicious cases. - A **throat culture** is the **gold standard** for diagnosing Group A Streptococcus (GAS) and is necessary to confirm the diagnosis and guide appropriate antibiotic treatment. *Start antibiotics based on clinical suspicion* - While clinical suspicion for **strep throat** is high, starting antibiotics without confirmation could contribute to **antibiotic resistance** and unnecessary side effects if the infection is viral. - Due to the potential for viral etiologies presenting similarly, it's crucial to confirm bacterial infection before initiating treatment. *Repeat the rapid antigen test* - Repeating the **RADT** may still yield a false negative, as its sensitivity is not 100%. - Given the high clinical suspicion and the potential for complications if untreated, a more definitive test is warranted. *Prescribe symptomatic treatment only* - While symptomatic treatment is appropriate for **viral pharyngitis**, untreated **bacterial strep throat** can lead to serious complications such as **rheumatic fever** or **glomerulonephritis**. - Without confirming the absence of a bacterial infection, simply providing symptomatic relief would be negligent.

Q: According to current evidence and emerging guidelines, what is the preferred primary treatment for initial Clostridium difficile infection in adults?

Fidaxomicin. Fidaxomicin - **Fidaxomicin** is a macrocyclic antibiotic that has demonstrated superior sustained clinical response rates compared to vancomycin for initial episodes of *C. difficile* infection, especially in preventing recurrence. - Its **narrow spectrum of activity** minimizes disruption to the gut microbiome, which is crucial for preventing subsequent infections. *Metronidazole* - While previously used for mild-to-moderate *C. difficile* infection (CDI), **metronidazole** is no longer recommended as primary therapy due to its inferior efficacy compared to vancomycin or fidaxomicin [1]. - Its use is generally reserved for situations where **vancomycin or fidaxomicin are unavailable**, or in very specific, mild cases [1]. *Vancomycin* - **Oral vancomycin** is an effective treatment for *C. difficile* infection and was long considered a first-line option [1]. However, evidence suggests fidaxomicin may be superior, particularly in preventing recurrence. - It is still a highly effective treatment for CDI, especially for **initial episodes that are moderate to severe**, but fidaxomicin offers an advantage in sustained response. *Rifaximin* - **Rifaximin** is primarily used to prevent recurrence of *C. difficile* infection after an initial course of vancomycin, rather than as a primary treatment. - It is a **non-absorbable antibiotic** with limited utility as a standalone initial therapy for active CDI.

Q: A 45-year-old male with chronic hepatitis B is being evaluated for antiviral therapy. His HBV DNA levels are elevated, and a liver biopsy shows moderate inflammation and fibrosis. What is the most appropriate antiviral regimen for this patient?

Tenofovir. ***Tenofovir*** - **Tenofovir** is a highly potent **nucleotide analog reverse transcriptase inhibitor** - **First-line therapy for chronic hepatitis B** due to its high barrier to resistance and potent viral suppression. *Interferon therapy* - **Interferon therapy** is an alternative, but it has significant **side effects** and is often **less preferred** for long-term treatment compared to nucleos(t)ide analogs [1]. - It involves weekly injections and can cause **flu-like symptoms**, psychiatric disturbances, and cytopenias [1]. *Lamivudine* - **Lamivudine** is a **nucleoside analog** that has a **low barrier to resistance**, meaning the virus can easily develop mutations that make the drug ineffective over time. - It is **not recommended** as a first-line agent for chronic hepatitis B due to the high risk of resistance. *Adefovir* - **Adefovir** is another **nucleotide analog** that has a **higher risk of nephrotoxicity** (kidney damage) compared to tenofovir. - It is **not a first-line treatment** option due to its less favorable safety profile and lower potency than tenofovir.

Question 1

A 45-year-old female presents with abdominal pain, jaundice, and fever. An abdominal CT scan reveals multiple liver abscesses, and aspiration yields anchovy paste-like pus. What is the most likely etiological agent responsible for these findings?

Accepted Answer

Entamoeba histolytica

Answer

Staphylococcus aureus

Answer

Klebsiella pneumoniae

Answer

Echinococcus granulosus

Question 2

Which type of hepatitis virus is most likely to progress to chronic hepatitis?

Accepted Answer

Hepatitis C

Answer

Hepatitis A

Answer

Hepatitis B

Answer

Hepatitis E

Question 3

A patient with acute myelogenous leukemia develops severe neutropenia following chemotherapy. He presents with fever and multiple nodular lung infiltrates. What are the likely pathogens and the preferred empirical therapy?

Accepted Answer

Fungal pneumonia in neutropenic patient

Answer

Atypical pneumonia in immunocompromised setting

Answer

Gram-positive bacterial pneumonia in immunocompromised patient

Answer

Respiratory infection in immunocompromised host

Question 4

A patient with diabetes presents with a black eschar on the nose and facial swelling. A biopsy shows broad, non-septate hyphal elements with right-angle branching. Assess the likely diagnosis and the urgency of the management required.

Accepted Answer

Mucormycosis, immediate aggressive treatment

Answer

Aspergillosis, elective treatment

Answer

Candidiasis, standard antifungal treatment

Answer

Dermatophytosis, topical treatment

Question 5

A patient presents with a bull's-eye rash and flu-like symptoms following a tick bite. What is the most likely diagnosis?

Accepted Answer

Lyme disease

Answer

Rocky Mountain spotted fever

Answer

Ehrlichiosis

Answer

Anaplasmosis

Question 6

A 53-year-old female with a history of systemic lupus erythematosus on prednisone presents with fever, cough, and pleuritic chest pain. Chest X-ray shows bilateral patchy infiltrates. Laboratory results indicate a white blood cell count of 3,000 and creatinine level of 1.4. Analyze and determine the diagnosis and initial treatment.

Accepted Answer

Pneumocystis pneumonia; TMP-SMX and steroids

Answer

Pulmonary embolism; anticoagulation

Answer

Acute lupus pneumonitis; increased steroids

Answer

Bacterial pneumonia; IV antibiotics

Question 7

In a patient with AIDS and a CD4 count of fewer than 50 cells/µL, which of the following opportunistic infections is most likely to occur?

Accepted Answer

Cryptococcus neoformans

Answer

Candida albicans

Answer

Aspergillus fumigatus

Answer

Histoplasma capsulatum

Question 8

A 22-year-old male with a sore throat, fever, and swollen lymph nodes presents with white patches on his tonsils. A rapid antigen detection test is negative. What is the next best step?

Accepted Answer

Perform a throat culture

Answer

Start antibiotics based on clinical suspicion

Answer

Repeat the rapid antigen test

Answer

Prescribe symptomatic treatment only

Question 9

According to current evidence and emerging guidelines, what is the preferred primary treatment for initial Clostridium difficile infection in adults?

Accepted Answer

Fidaxomicin

Answer

Rifaximin

Answer

Vancomycin

Answer

Metronidazole

Question 10

A 45-year-old male with chronic hepatitis B is being evaluated for antiviral therapy. His HBV DNA levels are elevated, and a liver biopsy shows moderate inflammation and fibrosis. What is the most appropriate antiviral regimen for this patient?

Accepted Answer

Tenofovir

Answer

Interferon therapy

Answer

Lamivudine

Answer

Adefovir

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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