Infectious Diseases Practice Questions

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 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 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 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 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.

Q: Which class of antibiotics is typically prescribed as the first-line therapy for community-acquired pneumonia?

Beta-lactams. ***Beta-lactams*** - **Beta-lactam antibiotics**, such as **amoxicillin** or **ceftriaxone**, are commonly recommended as first-line agents for **community-acquired pneumonia (CAP)**, especially in patients without recent antibiotic use or significant comorbidities. - They effectively target common bacterial pathogens like *Streptococcus pneumoniae* which are frequent causes of CAP. *Aminoglycosides* - **Aminoglycosides** are typically reserved for severe infections, particularly those caused by **gram-negative bacteria**, and are not first-line for uncomplicated CAP due to their potential for **nephrotoxicity** and **ototoxicity**. - They also have **poor activity** against atypical pathogens and *Streptococcus pneumoniae*. *Tetracyclines* - **Tetracyclines**, particularly **doxycycline**, can be used as an alternative or in combination for CAP, especially when **atypical pathogens** like *Mycoplasma pneumoniae* or *Chlamydophila pneumoniae* are suspected. - However, they are not universally recommended as the sole first-line agent, especially in areas with high rates of resistance. *Fluoroquinolones* - **Respiratory fluoroquinolones** (e.g., **levofloxacin**, **moxifloxacin**) are highly effective against CAP pathogens, including atypical bacteria and drug-resistant *Streptococcus pneumoniae*. - They are often reserved for patients with comorbidities, recent antibiotic use, or those requiring hospitalization, to help **prevent resistance development** when other agents are sufficient.

Q: A 45-year-old farmer presents with chronic cough and weight loss. Sputum microscopy reveals branching septate hyphae. Which antifungal agent should be initiated while awaiting the culture results?

Voriconazole. ***Voriconazole*** - The description of **branching septate hyphae** in a patient with chronic cough and weight loss is highly suggestive of **aspergillosis**. - **Voriconazole** is the **preferred first-line treatment** for invasive aspergillosis due to its superior efficacy, better tolerability, and convenience of administration compared to other antifungals. - It has excellent activity against *Aspergillus* species and achieves good tissue penetration. *Amphotericin B* - **Liposomal Amphotericin B** is an **alternative first-line agent** for invasive aspergillosis, particularly when voriconazole is contraindicated or unavailable. - However, it requires **intravenous administration**, has a higher incidence of **serious side effects** including nephrotoxicity and infusion-related reactions, making voriconazole the preferred initial choice when both are available. *Fluconazole* - **Fluconazole** is primarily active against *Candida* species and *Cryptococcus neoformans*. - It has **poor or no activity** against *Aspergillus* species and is therefore not an appropriate choice for suspected aspergillosis. *Itraconazole* - **Itraconazole** has activity against *Aspergillus* and can be used as an alternative or step-down therapy for chronic pulmonary aspergillosis. - However, it is **less effective** than voriconazole for invasive disease, and its **variable oral absorption** and numerous drug interactions make it less ideal for empiric therapy in acute presentations.

Q: A 32-year-old woman is advised on post-exposure prophylaxis (PEP) following a needlestick injury. What is the recommended regimen for HIV PEP?

Three-drug regimen. ***Three-drug regimen*** - A **three-drug regimen** is the **standard recommendation** for effective HIV post-exposure prophylaxis (PEP) to maximize the chances of preventing infection. - This approach typically involves a combination of two **nucleoside reverse transcriptase inhibitors (NRTIs)** and one **integrase strand transfer inhibitor (INSTI)** or a **protease inhibitor (PI)** [1]. *Single drug regimen* - A **single-drug regimen** is generally **insufficient** for preventing HIV infection after a significant exposure due to the risk of viral resistance and lower efficacy. - This approach would **not meet current guidelines** for optimal post-exposure prophylaxis. *Two-drug regimen* - While a **two-drug regimen** might be considered in very low-risk exposures or in situations where a three-drug regimen is contraindicated, it is **not the preferred standard**. - The **efficacy is lower** compared to a three-drug regimen, especially when the source virus's resistance profile is unknown or the exposure risk is moderate to high [1]. *Four-drug regimen* - A **four-drug regimen** is **not routinely recommended** for HIV PEP as there is no evidence that adding a fourth drug significantly improves efficacy over a three-drug regimen. - It would increase the risk of **drug-related toxicities and side effects** without additional benefit in most cases.

Q: A 30-year-old woman with recent travel to Southeast Asia presents with an eschar at the site of a chigger bite and a febrile illness. What is the most appropriate initial treatment?

Doxycycline. ***Doxycycline*** - This presentation is highly suggestive of **scrub typhus**, an infectious disease endemic to Southeast Asia, characterized by a **febrile illness** and an **eschar** at the site of a chigger bite. - **Doxycycline** is the drug of choice for treating scrub typhus, as well as other rickettsial infections, due to its efficacy against *Orientia tsutsugamushi*. *Azithromycin* - While azithromycin can be used as an alternative for scrub typhus, particularly in pregnant women or young children, it is **less effective** than doxycycline, especially in severe cases. - It is typically considered when doxycycline is contraindicated. *Ciprofloxacin* - Ciprofloxacin is a **fluoroquinolone antibiotic** that is generally not effective against *Orientia tsutsugamushi* or other rickettsial infections. - It targets bacterial DNA gyrase and topoisomerase IV, mechanisms that are not crucial for eradicating this specific pathogen. *Amoxicillin* - **Amoxicillin** is a penicillin-class antibiotic that is ineffective against atypical bacteria like *Orientia tsutsugamushi* because it targets bacterial cell wall synthesis which is not a primary mechanism of action against rickettsial organisms. - It would not be an appropriate treatment for scrub typhus.

Q: A 40-year-old female with systemic lupus erythematosus on chronic steroids presents with fever, cough, and shortness of breath. Chest X-ray shows bilateral infiltrates. Laboratory results indicate a white blood cell count of 2,000 and a PaO2 of 60 on room air. What is the best therapeutic approach for this patient?

TMP-SMX + corticosteroids. ***TMP-SMX + corticosteroids*** - The patient's presentation (**fever, cough, shortness of breath, bilateral infiltrates, low WBC, hypoxemia**) in a patient with **SLE on chronic steroids** strongly suggests **Pneumocystis jirovecii pneumonia (PJP)** [1]. - **Trimethoprim-sulfamethoxazole (TMP-SMX)** is the first-line treatment for PJP, and **corticosteroids** are indicated for moderate to severe PJP (PaO2 35 mmHg) to mitigate inflammatory lung damage [1]. *Empiric broad-spectrum abx + IVIG* - While empiric broad-spectrum antibiotics might be considered for unknown infections, **PJP is highly suspected** given the patient's immunosuppression [3], making targeted therapy with TMP-SMX more appropriate. - **Intravenous immunoglobulin (IVIG)** is typically used for antibody deficiencies or autoimmune disorders and has no primary role in treating PJP. *Plasma exchange + supportive care* - **Plasma exchange** is used to remove harmful antibodies or immune complexes, primarily in severe autoimmune flares or conditions like thrombotic thrombocytopenic purpura [4], not for infectious pulmonary infiltrates. - While supportive care is always necessary, it's insufficient alone to treat a potentially life-threatening infection like PJP. *Broad-spectrum abx + granulocyte colony-stimulating factor (G-CSF)* - **Broad-spectrum antibiotics** alone are not effective against *Pneumocystis jirovecii*, which is a fungus, not bacteria [1]. - **G-CSF** is used to stimulate neutrophil production, beneficial in severe neutropenia [2], but not a primary treatment for PJP or the underlying cause of lung infiltrates in this scenario.

Question 1

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 2

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 3

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 4

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 5

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

Question 6

Which class of antibiotics is typically prescribed as the first-line therapy for community-acquired pneumonia?

Accepted Answer

Beta-lactams

Answer

Aminoglycosides

Answer

Tetracyclines

Answer

Fluoroquinolones

Question 7

A 45-year-old farmer presents with chronic cough and weight loss. Sputum microscopy reveals branching septate hyphae. Which antifungal agent should be initiated while awaiting the culture results?

Accepted Answer

Voriconazole

Answer

Amphotericin B

Answer

Fluconazole

Answer

Itraconazole

Question 8

A 32-year-old woman is advised on post-exposure prophylaxis (PEP) following a needlestick injury. What is the recommended regimen for HIV PEP?

Accepted Answer

Three-drug regimen

Answer

Single drug regimen

Answer

Two-drug regimen

Answer

Four-drug regimen

Question 9

A 30-year-old woman with recent travel to Southeast Asia presents with an eschar at the site of a chigger bite and a febrile illness. What is the most appropriate initial treatment?

Accepted Answer

Doxycycline

Answer

Azithromycin

Answer

Ciprofloxacin

Answer

Amoxicillin

Question 10

A 40-year-old female with systemic lupus erythematosus on chronic steroids presents with fever, cough, and shortness of breath. Chest X-ray shows bilateral infiltrates. Laboratory results indicate a white blood cell count of 2,000 and a PaO2 of 60 on room air. What is the best therapeutic approach for this patient?

Accepted Answer

TMP-SMX + corticosteroids

Answer

Empiric broad-spectrum abx + IVIG

Answer

Plasma exchange + supportive care

Answer

Broad-spectrum abx + granulocyte colony-stimulating factor (G-CSF)

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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