Infectious Diseases Practice Questions

Q: A 45-year-old man presents with diarrhea and abdominal pain. A biopsy reveals numerous macrophages filled with acid-fast organisms compressing lymphatic vessels. What is the most likely diagnosis?

Mycobacterium avium. ***Mycobacterium avium*** - The presence of **acid-fast organisms (AFO)** within macrophages compressing lymphatic vessels in a patient with diarrhea and abdominal pain is characteristic of **Mycobacterium avium complex (MAC)**. - MAC infection often causes widespread gastrointestinal involvement, particularly in immunocompromised individuals, leading to malabsorption and weight loss. *Giardia lamblia* - **Giardia lamblia** causes giardiasis, characterized by diarrhea, abdominal cramps, and malabsorption [2]. - However, giardia is a **flagellated protozoan** and would not appear as acid-fast organisms within macrophages [2]. *Mycobacterium tuberculosis* - While **Mycobacterium tuberculosis** is an acid-fast organism and can cause gastrointestinal disease, it typically presents with granulomas and caseous necrosis, rather than widespread macrophage infiltration with intact organisms compressing lymphatic vessels in this specific manner. - Gastrointestinal tuberculosis is less common than MAC in this presentation. *Entamoeba histolytica* - **Entamoeba histolytica** causes amebic dysentery, characterized by bloody diarrhea, and is associated with flask-shaped ulcers in the colon [1]. - It is a **protozoan parasite** and would not be identified as an acid-fast organism within macrophages [1].

Q: A 58-year-old male presents with fever, cough, and pleuritic chest pain. His sputum culture grows Streptococcus pneumoniae (penicillin-sensitive). For outpatient oral therapy, what is the most appropriate antibiotic?

Amoxicillin. **Amoxicillin** (Correct Answer) - **Amoxicillin** is the first-line agent for community-acquired pneumonia caused by **penicillin-sensitive Streptococcus pneumoniae** due to its excellent efficacy, safety profile, and narrow spectrum. - Given that the organism is confirmed to be **penicillin-sensitive**, amoxicillin is the most appropriate choice for **outpatient oral therapy**. - It provides adequate coverage with minimal collateral damage and is cost-effective. *Azithromycin* (Incorrect) - While **azithromycin** covers atypical pathogens and is commonly used empirically for community-acquired pneumonia, its use for penicillin-sensitive *S. pneumoniae* is less effective than amoxicillin due to increasing macrolide resistance in some *S. pneumoniae* strains. - It would be a consideration if atypical pathogens were suspected or if the patient had a penicillin allergy, neither of which is indicated here. *Ciprofloxacin* (Incorrect) - **Ciprofloxacin** is a fluoroquinolone mainly used for gram-negative infections, complicated urinary tract infections, and sometimes for pneumonia, but it is generally reserved for situations where other antibiotics are not suitable or for specific indications like **Pseudomonas aeruginosa**. - Its broad-spectrum nature and potential for **collateral damage** (e.g., *C. difficile* infection, resistance development) make it a less preferred choice when a penicillin-sensitive organism is identified and a narrower-spectrum agent is available. *Vancomycin* (Incorrect) - **Vancomycin** is an intravenous antibiotic used for **methicillin-resistant Staphylococcus aureus (MRSA)** or **penicillin-resistant S. pneumoniae**, which is not the case here. - It is not available as an oral formulation for systemic infections (oral vancomycin is only used for *C. difficile* colitis) and would be inappropriate for **outpatient oral therapy** of penicillin-sensitive *S. pneumoniae*.

Q: A patient presents with severe abdominal pain and jaundice. Imaging reveals calcified cysts in the liver, and serological testing is positive for Echinococcus. What is a potential complication of this infection?

Secondary bacterial infection of cysts. ***Secondary bacterial infection of cysts*** - **Hydatid cysts** can become secondarily infected, typically after rupture or surgical manipulation, leading to an **abscess formation** within the liver. - This complication can present with features like fever, worsening abdominal pain, and an elevated **white blood cell count**, distinct from the initial presentation. *Rupture of cysts leading to anaphylactic shock* - While rupture of **hydatid cysts** can lead to **anaphylactic shock** due to the release of hydatid fluid, it is not the *most common immediate complication* or the scenario implied by abdominal pain and jaundice. - **Anaphylaxis** implies a rapid, severe systemic allergic reaction, which is a life-threatening acute event. *Portal hypertension due to cyst compression* - While large cysts can compress structures, significant **portal hypertension** due to direct compression of the portal vein by **hydatid cysts** is rare. - More commonly, portal hypertension is a complication of advanced **cirrhosis**, not typically direct cyst compression in the early stages described. *No significant complications* - **Echinococcosis** (hydatid disease) is a serious parasitic infection that almost always leads to significant morbidity if left untreated. - Cysts grow over time and inevitably cause **organ dysfunction**, pain, obstruction, or other complications.

Q: In a patient with suspected tuberculosis, what is the most appropriate initial diagnostic test?

Chest X-ray. ***Chest X-ray*** - A **chest X-ray** is usually the **initial diagnostic test** for suspected active pulmonary tuberculosis (TB) to assess for lung involvement, such as **infiltrates, cavitations, or effusions** [1]. - While not definitive, it helps to **localize the disease** and can guide further diagnostic steps [1]. *Tuberculin skin test* - The **tuberculin skin test (TST)**, also known as the **Mantoux test**, primarily assesses for **latent TB infection** or previous exposure, not active disease, and cannot differentiate between the two. - A **positive TST** indicates an immune response to *Mycobacterium tuberculosis* but requires further investigation to rule out active disease. *Interferon-gamma release assay* - **Interferon-gamma release assays (IGRAs)**, like the TST, are used to diagnose **latent TB infection**, and cannot distinguish between latent and active TB [2]. - While **more specific** than TST, a positive IGRA still necessitates additional tests like a chest X-ray and sputum analysis to confirm active disease [2]. *Acid-fast bacillus (AFB) staining of sputum* - **AFB staining and microscopy** of sputum is a rapid method to identify active TB by detecting mycobacteria, providing presumptive evidence for diagnosis and guiding immediate isolation [1]. - However, it's typically performed **after an initial imaging study** like a chest X-ray suggests pulmonary involvement and before culture for definitive diagnosis [1].

Q: A patient who recently returned from a hiking trip in the Rocky Mountains presents with fever, headache, and a rash on the wrists and ankles that is progressing to the trunk. What is the most likely diagnosis, and what are the key steps for confirmation of this diagnosis?

Rocky Mountain spotted fever. **Rocky Mountain spotted fever** - The classic triad of **fever, headache, and a centripetal rash** (starting on wrists/ankles and spreading to trunk) in a patient from an endemic area (Rocky Mountains) is highly characteristic of **Rocky Mountain spotted fever (RMSF)** [1], [2]. - Confirmation involves **serologic testing** (indirect immunofluorescence assay for IgG and IgM antibodies to *Rickettsia rickettsii*) and, in some cases, **PCR** of skin biopsy from the rash [2]. *Lyme disease* - While Lyme disease is also a tick-borne illness, its hallmark rash is **erythema migrans** (a target-like lesion), which is distinct from the described maculopapular to petechial rash of RMSF [3]. - Neurological, cardiac, and arthritic manifestations develop later in Lyme disease, and the acute presentation differs significantly. *Ehrlichiosis* - Ehrlichiosis typically presents with fever, headache, body aches, and fatigue, but a **rash is less common** (occurring in <10% of cases) and usually appears later in the course, without the characteristic centripetal progression of RMSF [3]. - Microscopic examination of peripheral blood smears may reveal **morulae within phagocytes**, a key diagnostic feature differentiating it from RMSF. *Anaplasmosis* - Anaplasmosis shares symptoms like fever, headache, and muscle aches but **rarely causes a rash** [3]. - Like ehrlichiosis, it can be diagnosed by finding **morulae within granulocytes** on a peripheral blood smear, which is not typical for RMSF [3].

Q: A healthcare worker exposed to a needlestick injury from a hepatitis B positive patient tests positive for HBsAg after 3 months. What is the next best step in management?

Start antiviral therapy. ***Start antiviral therapy*** - A positive **HBsAg** (Hepatitis B surface antigen) at 3 months indicates **active hepatitis B infection** [1]. - Since the patient has already developed chronic infection (indicated by positive HBsAg after 3 months), **antiviral therapy** is the appropriate next step to manage the infection, prevent disease progression, and reduce transmission risk [1]. *Administer hepatitis B vaccine* - The vaccine would have been appropriate for **pre-exposure prophylaxis** or immediate post-exposure prophylaxis if the worker was not previously vaccinated and tested negative for HBsAg and HBsAb following exposure. - Administering the vaccine after the development of active infection (positive HBsAg) is **ineffective** as it is designed to prevent infection, not treat it. *Administer hepatitis B immunoglobulin* - **Hepatitis B immunoglobulin (HBIG)** provides passive immunity and is typically administered as part of **post-exposure prophylaxis (PEP)** immediately after exposure, ideally within 24 hours (and up to 7 days), especially for unvaccinated individuals, in conjunction with the vaccine [2]. - It is not indicated for treating established active or chronic hepatitis B infection, as the patient already has a positive HBsAg. *Monitor liver function tests* - Monitoring **liver function tests (LFTs)** is an important component of managing hepatitis B, both acutely and chronically, to assess liver damage and disease progression [1]. - However, simply monitoring LFTs without initiating specific treatment is **insufficient** in a patient with confirmed active hepatitis B infection. Treatment is necessary to prevent further liver damage and complications.

Q: What is the role of fecal microbiota transplantation in the treatment of recurrent Clostridium difficile infection?

Beneficial in select cases. ***Beneficial in select cases*** - **Fecal microbiota transplantation (FMT)** is highly effective in restoring the normal gut microbiota in patients with **recurrent *Clostridium difficile* infection (CDI)**, preventing further episodes. - It is particularly recommended for patients who have had at least **three episodes of mild to moderate CDI** unresponsive to antibiotic therapy, or at least **two episodes of severe CDI** requiring hospitalization. *First-line treatment option* - **FMT** is not a **first-line treatment** for *C. difficile* infection; initial episodes are typically managed with oral antibiotics like **vancomycin** or **fidaxomicin**. - Its role is primarily in preventing **recurrence** after standard antibiotic treatment has failed. *Only effective with antibiotics* - **FMT** is typically administered *after* a course of antibiotics has cleared the acute *C. difficile* infection, with its benefit coming from **restoring microbial diversity** rather than acting synergistically with antibiotics during active infection. - While sometimes antibiotics are used to clear the initial infection before FMT, the effectiveness of FMT itself in preventing recurrence is largely independent of concurrent antibiotic use at the time of transplantation. *No significant benefit* - Numerous studies, including randomized controlled trials, have demonstrated that **FMT** significantly **reduces recurrence rates** of *C. difficile* infection, often with success rates exceeding 85%. - This high efficacy position's FMT as a crucial intervention for patients with recurrent CDI.

Q: A patient with AIDS presents with shortness of breath and a dry cough. A chest X-ray shows interstitial infiltrates. What is the most likely diagnosis?

Pneumocystis jirovecii pneumonia. ***Pneumocystis jirovecii pneumonia*** - **Pneumocystis jirovecii pneumonia (PJP)** is an **opportunistic infection** common in **AIDS patients** with CD4 counts typically below 200 cells/mm³ [1]. - Classic presentation includes **shortness of breath**, **dry cough**, and diffuse **interstitial infiltrates** on chest X-ray [1]. *Tuberculosis* - While TB is common in AIDS patients, the typical presentation often involves **cavitary lesions** or **upper lobe infiltrates**, and can present with systemic symptoms like **night sweats** and **weight loss**, which are not specified here [1]. - The **interstitial pattern** is less characteristic of primary pulmonary TB in immunocompromised patients, though atypical presentations are possible [1]. *Kaposi sarcoma* - **Kaposi sarcoma** in the lungs typically presents with **nodular** or **peribronchovascular infiltrates** and can cause pleural effusions, not the diffuse interstitial pattern seen here [2]. - It is a **vasoproliferative malignancy**, less likely to cause acute respiratory symptoms as the primary manifestation in this context compared to infection. *Community-acquired pneumonia* - **Community-acquired pneumonia (CAP)** in AIDS patients can be caused by various typical bacteria, but often presents with **lobar consolidation** or more focal infiltrates, and may be accompanied by fever and productive cough [2]. - The **diffuse interstitial infiltrates** and **dry cough** are less typical for most bacterial CAPs and point more specifically towards PJP in an AIDS patient [1].

Q: A patient with a history of organ transplantation presents with fever and a dry cough. Imaging reveals diffuse interstitial pneumonia. What is the most likely diagnosis?

Cytomegalovirus infection. ***Cytomegalovirus infection*** - **CMV pneumonia** is a common and serious opportunistic infection in **transplant recipients** due to their immunosuppressed state. - Presentation with **fever**, **dry cough**, and **diffuse interstitial infiltrates** on imaging is highly characteristic of CMV pneumonitis. *Bacterial pneumonia* - While possible, bacterial pneumonia typically presents with a **productive cough**, **purulent sputum**, and often **lobar consolidation** rather than diffuse interstitial infiltrates. - **Immunosuppression** does increase the risk, but the classic imaging and cough characteristics point away from a common bacterial etiology. *Fungal pneumonia* - **Fungal infections** often cause pneumonia in transplant patients but typically present with nodular lesions, cavitations, or discrete infiltrates, sometimes with a more indolent course, rather than diffuse interstitial pneumonia. - Common fungal pathogens like *Pneumocystis jirovecii* can cause diffuse interstitial pneumonia but often present with more severe **hypoxemia** and imaging may show a **ground-glass appearance**. *Tuberculosis* - **Tuberculosis** can reactivate in transplant patients and cause pneumonia, but it usually presents with **upper lobe infiltrates**, **cavitation**, or **miliary patterns**, and often a more chronic cough, sometimes with hemoptysis and night sweats. - **Diffuse interstitial pneumonia** as the primary presentation is less typical for tuberculosis.

Q: A patient from India presents with high fever, hepatosplenomegaly, and pancytopenia. A blood smear shows Leishmania donovani. What is the recommended treatment?

Amphotericin B. **Amphotericin B** - **Liposomal amphotericin B** is the drug of choice for visceral leishmaniasis (kala-azar) caused by *Leishmania donovani*, especially in regions like India where resistance to older drugs is prevalent [1]. - Its effectiveness stems from its ability to form pores in the parasite and fungal cell membranes, leading to cell death. *Chloroquine* - **Chloroquine** is an antimalarial drug and is not effective against *Leishmania* infections. - It acts by preventing the detoxification of heme inside the malarial parasite. *Pentavalent antimony* - While **pentavalent antimonials** (e.g., sodium stibogluconate) were historically the first-line treatment for leishmaniasis, significant resistance has emerged, particularly in regions like India [1]. - Their use is now limited due to toxicity and widespread treatment failures in many endemic areas. *Metronidazole* - **Metronidazole** is an antimicrobial effective against various anaerobic bacteria and protozoa like *Giardia* and *Trichomonas*, but it has no activity against *Leishmania donovani*. - It works by disrupting DNA synthesis in susceptible organisms.

Question 1

A 45-year-old man presents with diarrhea and abdominal pain. A biopsy reveals numerous macrophages filled with acid-fast organisms compressing lymphatic vessels. What is the most likely diagnosis?

Accepted Answer

Mycobacterium avium

Answer

Giardia lamblia

Answer

Mycobacterium tuberculosis

Answer

Entamoeba histolytica

Question 2

A 58-year-old male presents with fever, cough, and pleuritic chest pain. His sputum culture grows Streptococcus pneumoniae (penicillin-sensitive). For outpatient oral therapy, what is the most appropriate antibiotic?

Accepted Answer

Amoxicillin

Answer

Azithromycin

Answer

Ciprofloxacin

Answer

Vancomycin

Question 3

A patient presents with severe abdominal pain and jaundice. Imaging reveals calcified cysts in the liver, and serological testing is positive for Echinococcus. What is a potential complication of this infection?

Accepted Answer

Secondary bacterial infection of cysts

Answer

Portal hypertension due to cyst compression

Answer

Rupture of cysts leading to anaphylactic shock

Answer

No significant complications

Question 4

In a patient with suspected tuberculosis, what is the most appropriate initial diagnostic test?

Accepted Answer

Chest X-ray

Answer

Tuberculin skin test

Answer

Interferon-gamma release assay

Answer

Acid-fast bacillus (AFB) staining of sputum

Question 5

A patient who recently returned from a hiking trip in the Rocky Mountains presents with fever, headache, and a rash on the wrists and ankles that is progressing to the trunk. What is the most likely diagnosis, and what are the key steps for confirmation of this diagnosis?

Accepted Answer

Rocky Mountain spotted fever

Answer

Lyme disease

Answer

Ehrlichiosis

Answer

Anaplasmosis

Question 6

A healthcare worker exposed to a needlestick injury from a hepatitis B positive patient tests positive for HBsAg after 3 months. What is the next best step in management?

Accepted Answer

Start antiviral therapy

Answer

Administer hepatitis B vaccine

Answer

Administer hepatitis B immunoglobulin

Answer

Monitor liver function tests

Question 7

What is the role of fecal microbiota transplantation in the treatment of recurrent Clostridium difficile infection?

Accepted Answer

Beneficial in select cases

Answer

First-line treatment option

Answer

Only effective with antibiotics

Answer

No significant benefit

Question 8

A patient with AIDS presents with shortness of breath and a dry cough. A chest X-ray shows interstitial infiltrates. What is the most likely diagnosis?

Accepted Answer

Pneumocystis jirovecii pneumonia

Answer

Tuberculosis

Answer

Kaposi sarcoma

Answer

Community-acquired pneumonia

Question 9

A patient with a history of organ transplantation presents with fever and a dry cough. Imaging reveals diffuse interstitial pneumonia. What is the most likely diagnosis?

Accepted Answer

Cytomegalovirus infection

Answer

Bacterial pneumonia

Answer

Fungal pneumonia

Answer

Tuberculosis

Question 10

A patient from India presents with high fever, hepatosplenomegaly, and pancytopenia. A blood smear shows Leishmania donovani. What is the recommended treatment?

Accepted Answer

Amphotericin B

Answer

Chloroquine

Answer

Metronidazole

Answer

Pentavalent antimony

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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