Infectious Diseases Practice Questions

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: 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: 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 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.

Q: A 45-year-old woman presents with a persistent cough, weight loss, and night sweats. A chest X-ray reveals a cavitary lesion in the upper lobe, and sputum is positive for acid-fast bacilli. Which of the following is the most appropriate initial treatment regimen?

Isoniazid, rifampin, pyrazinamide, and ethambutol. ***Isoniazid, rifampin, pyrazinamide, and ethambutol*** - This **four-drug regimen** is the standard initial treatment for active **tuberculosis** due to the high risk of drug resistance with fewer agents [1]. - The combination of these drugs increases treatment efficacy and reduces the likelihood of developing **multi-drug resistant TB** [1]. *Isoniazid and rifampin only* - This two-drug regimen is used for the **continuation phase** of TB treatment, after an initial intensive phase with more drugs [1]. - Administering only two drugs initially for active TB could lead to **treatment failure** and the development of drug-resistant strains [1]. *Rifampin and pyrazinamide only* - This combination is insufficient for initial treatment of active TB, as it lacks the broad coverage needed to prevent **resistance** and ensure optimal eradication of the bacteria [1]. - Both isoniazid and ethambutol are essential components of the initial phase to achieve **sterilization** and prevent the emergence of resistant organisms. *Streptomycin and ethambutol* - **Streptomycin** is an older injectable drug sometimes used in specific cases, but it is not a first-line backbone for initial treatment, especially given its toxicities [1]. - This combination lacks the central powerful oral agents like **isoniazid** and **rifampin** which are crucial for effective initial therapy.

Q: A 28-year-old man presents with fever, chills, and a rash that began on the wrists and ankles and spread to the trunk. What is the most likely diagnosis?

Rocky Mountain spotted fever. ***Rocky Mountain spotted fever*** - The classic presentation involves **fever, chills**, and a **rash** that starts on the **wrists and ankles** and spreads centrally to the trunk [1]. - This is a **tick-borne illness** caused by *Rickettsia rickettsii*, a highly suggestive clinical picture [1]. *Lyme disease* - Characterized by an expanding **erythema migrans** (bull's-eye rash), which is typically large and annular, not a diffuse rash spreading from extremities. - While it can cause fever and chills, the rash morphology and spread pattern are inconsistent with this case description. *Measles* - Presents with a **maculopapular rash** that typically starts on the **face** and spreads downwards to the trunk and extremities, not initiating on the wrists and ankles. - Associated with the "3 Cs": **cough, coryza, and conjunctivitis**, and possibly **Koplik spots**, which are not mentioned. *Meningococcemia* - Often presents with an abrupt onset of **fever, headache, stiff neck**, and a **petechial or purpuric rash**, which does not typically start on the wrists and ankles. - The rash is usually diffuse and can rapidly progress to **purpura fulminans**, often indicating severe sepsis.

Q: A 60-year-old male with diabetes presents with fever, cough, and pleuritic chest pain. A chest X-ray reveals right lower lobe consolidation. What is the most appropriate initial antibiotic therapy?

Ceftriaxone and azithromycin. ***Ceftriaxone and azithromycin*** - This combination provides broad-spectrum coverage for **community-acquired pneumonia (CAP)**, targeting both typical bacteria (e.g., *Streptococcus pneumoniae*) and atypical pathogens (e.g., *Mycoplasma pneumoniae*, *Chlamydophila pneumoniae*) [1]. - Ceftriaxone is a **third-generation cephalosporin** effective against Gram-positive bacteria, while azithromycin is a **macrolide** covering atypical organisms and providing additional anti-inflammatory effects [2]. *Amoxicillin* - While effective against common pathogens like *Streptococcus pneumoniae*, **amoxicillin alone** may not adequately cover atypical pathogens or resistant strains, especially in patients with comorbidities like diabetes [3]. - It does not cover **atypical pneumonia**, which can be a significant cause of CAP. *Azithromycin* - Azithromycin is effective against **atypical pathogens** but does not provide sufficient coverage for common typical bacteria like *Streptococcus pneumoniae* when used as monotherapy in patients with comorbidities [2]. - Monotherapy with a macrolide like azithromycin is generally reserved for otherwise healthy individuals with **mild CAP**. *Levofloxacin* - Levofloxacin is a **respiratory fluoroquinolone** that offers broad-spectrum coverage, including typical and atypical pathogens, and can be used as monotherapy [2]. - However, due to concerns about increasing **antibiotic resistance** and potential side effects (e.g., QT prolongation, tendon rupture), it is often reserved for patients who cannot tolerate beta-lactams or macrolides, or in cases of severe CAP not responding to initial therapy.

Q: A 25-year-old woman presents with a severe sore throat, fever, and difficulty swallowing. Examination reveals swollen tonsils with white exudate and tender cervical lymphadenopathy. What is the most likely diagnosis?

Streptococcal pharyngitis. Streptococcal pharyngitis - The combination of severe sore throat, fever, swollen tonsils with white exudate, and tender cervical lymphadenopathy is highly suggestive of Group A Streptococcus (GAS) infection. - This clinical presentation aligns with the Centor criteria for diagnosing strep throat, which includes tonsillar exudates, tender anterior cervical lymph nodes, absence of cough, and history of fever. Viral pharyngitis - While viral pharyngitis can cause sore throat and fever, it often presents with additional symptoms like cough, rhinorrhea (runny nose), and conjunctivitis, which are absent here. - White exudates on the tonsils are less common and typically not as prominent in viral cases compared to bacterial infections. Epstein-Barr virus infection - Infectious mononucleosis due to EBV can present with severe pharyngitis, exudative tonsillitis, fever, and lymphadenopathy, but it often includes fatigue, splenomegaly, and atypical lymphocytosis, which are not mentioned in this case. - While it's a possibility, the classic presentation without other distinguishing features makes streptococcal pharyngitis more likely. Diphtheria - Diphtheria is characterized by a greyish-white pseudomembrane that is firmly attached to the tonsils and pharynx and bleeds if scraped, which is not described [1]. - This disease is now rare due to vaccination and typically involves more systemic toxicity and potential airway obstruction [1].

Q: A 50-year-old patient presents with bloody diarrhea and a history of travel to India. Stool examination reveals trophozoites containing ingested red blood cells. What is the most likely diagnosis?

Amoebiasis. Amoebiasis - The presence of **bloody diarrhea**, a history of **travel to India** (an endemic area) [1], and **trophozoites containing ingested red blood cells** are classic hallmarks of amoebiasis caused by **Entamoeba histolytica**. [2] - **E. histolytica** trophozoites invade the intestinal mucosa and consume red blood cells, leading to ulceration and bloody stools. Giardiasis - Characterized by **non-bloody, greasy, foul-smelling diarrhea**, abdominal cramps, and bloating. - Stool examination would typically reveal **Giardia lamblia trophozoites or cysts**, but not trophozoites with ingested red blood cells. Hookworm infection - Typically causes **iron deficiency anemia** due to chronic blood loss from the gut. [3] - While it can cause gastrointestinal symptoms, **bloody diarrhea** with trophozoites containing ingested red blood cells is not a characteristic finding. Schistosomiasis - Primarily causes symptoms related to the migration of **schistosome eggs** in various organs. - **Intestinal schistosomiasis** can lead to bloody diarrhea, but stool examination would show **schistosome eggs**, not amoebic trophozoites ingesting red blood cells.

Question 1

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 2

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 3

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 4

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 5

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

Question 6

A 45-year-old woman presents with a persistent cough, weight loss, and night sweats. A chest X-ray reveals a cavitary lesion in the upper lobe, and sputum is positive for acid-fast bacilli. Which of the following is the most appropriate initial treatment regimen?

Accepted Answer

Isoniazid, rifampin, pyrazinamide, and ethambutol

Answer

Isoniazid and rifampin only

Answer

Rifampin and pyrazinamide only

Answer

Streptomycin and ethambutol

Question 7

A 28-year-old man presents with fever, chills, and a rash that began on the wrists and ankles and spread to the trunk. What is the most likely diagnosis?

Accepted Answer

Rocky Mountain spotted fever

Answer

Lyme disease

Answer

Measles

Answer

Meningococcemia

Question 8

A 60-year-old male with diabetes presents with fever, cough, and pleuritic chest pain. A chest X-ray reveals right lower lobe consolidation. What is the most appropriate initial antibiotic therapy?

Accepted Answer

Ceftriaxone and azithromycin

Answer

Azithromycin

Answer

Amoxicillin

Answer

Levofloxacin

Question 9

A 25-year-old woman presents with a severe sore throat, fever, and difficulty swallowing. Examination reveals swollen tonsils with white exudate and tender cervical lymphadenopathy. What is the most likely diagnosis?

Accepted Answer

Streptococcal pharyngitis

Answer

Viral pharyngitis

Answer

Epstein-Barr virus infection

Answer

Diphtheria

Question 10

A 50-year-old patient presents with bloody diarrhea and a history of travel to India. Stool examination reveals trophozoites containing ingested red blood cells. What is the most likely diagnosis?

Accepted Answer

Amoebiasis

Answer

Giardiasis

Answer

Hookworm infection

Answer

Schistosomiasis

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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