Infectious Diseases Practice Questions

Q: A 50-year-old farmer presents with cough, fever, and weight loss. CXR shows upper lobe cavitary lesions. Sputum culture reveals acid-fast bacilli resistant to isoniazid and rifampin. What is the next best drug?

Fluoroquinolone. **Fluoroquinolone** - In cases of **multidrug-resistant tuberculosis (MDR-TB)**, which is defined by specific resistance to both **isoniazid** and **rifampin**, fluoroquinolones are a crucial second-line agent [1]. - They demonstrate excellent **mycobactericidal activity** and are a cornerstone of MDR-TB treatment regimens [1]. *Linezolid* - While **Linezolid** is used in highly resistant TB cases (XDR-TB), it is generally reserved for situations where other core second-line drugs (like fluoroquinolones) cannot be used or are resistant. - Its use often carries a higher risk of **myelosuppression** and **neuropathy**, making it less preferred as an initial choice for MDR-TB. *Ethambutol* - **Ethambutol** is a first-line antitubercular drug, but it is typically used in conjunction with isoniazid and rifampin to prevent resistance development [1]. - It would not be the "next best" drug when **TB is already resistant to isoniazid and rifampin**, as single-drug therapy is ineffective for MDR-TB and could lead to further resistance. *Pyrazinamide* - **Pyrazinamide** is another first-line drug primarily effective against semi-dormant bacilli in acidic environments [1]. - Similar to ethambutol, it is not appropriate as the "next best" drug to manage **MDR-TB** when resistance to standard first-line agents has already been identified.

Q: A 45-year-old male presents with fever, cough, and cavitary lesion on CXR. What is the most likely diagnosis?

TB. ***TB*** - **Cavitary lesions** on CXR, accompanied by **fever and cough**, are highly suggestive of **pulmonary tuberculosis**, particularly in endemic areas or with risk factors [1]. - **Mycobacterium tuberculosis** leads to granuloma formation, which can undergo caseous necrosis and cavitation [2]. *Sarcoidosis* - Characterized by **non-caseating granulomas** and typically presents with **bilateral hilar lymphadenopathy** and interstitial lung disease, less commonly with cavitary lesions. - While it can cause cough and fever, cavitary lesions are not its hallmark presentation. *Lung cancer* - Can present with cough and a lung mass, which may sometimes cavitate, but fever is not a primary symptom unless there is an associated infection or paraneoplastic syndrome. - A persistent **cavitary lesion** without other typical features of malignancy makes **TB** a more probable diagnosis, especially given the fever. *Lung abscess* - A **lung abscess** is a necrotic infection of the lung parenchyma, resulting in a cavity filled with pus, often caused by aspiration. - While it typically presents with fever and cough and can show a cavitary lesion on CXR, the question doesn't provide context for aspiration or an acute bacterial infection. **TB** is a more systemic and chronic disease with these findings.

Q: A 45-year-old HIV-positive man presents with fever and cough. Sputum culture shows acid-fast bacilli. Which of the following drugs is essential in the treatment regimen?

Isoniazid. ***Isoniazid*** - The presence of **acid-fast bacilli** (AFB) in sputum, especially in an **HIV-positive** individual with fever and cough, strongly indicates **tuberculosis (TB)** [1]. - **Isoniazid** is a cornerstone drug in **first-line anti-tuberculosis therapy** and is essential for effective treatment [1]. *Doxycycline* - **Doxycycline** is a tetracycline antibiotic primarily used for bacterial infections like **atypical pneumonia**, Lyme disease, and certain sexually transmitted infections. - It has **no significant activity against Mycobacterium tuberculosis** and is not part of TB treatment. *Amoxicillin* - **Amoxicillin** is a penicillin-class antibiotic effective against a range of common bacterial infections, but it is **ineffective against mycobacteria**. - It would not be used to treat **tuberculosis**. *Ciprofloxacin* - **Ciprofloxacin** is a fluoroquinolone antibiotic used for various bacterial infections, including some respiratory and urinary tract infections. - While some fluoroquinolones are used as **second-line agents** in specific multi-drug resistant TB regimens, **ciprofloxacin** is not a first-line drug and is generally reserved for particular circumstances, unlike isoniazid which is essential for initial therapy.

Q: A 40-year-old patient presents with frequent watery diarrhea after a recent course of antibiotics. Stool toxin assay is positive for Clostridium difficile. What is the most appropriate treatment?

Oral vancomycin. ***Oral vancomycin*** - **Oral vancomycin** is the **first-line treatment** for *Clostridium difficile* infection (CDI) due to its high efficacy against *C. difficile* and its inability to be absorbed systemically, allowing high concentrations to remain in the gut lumen [1]. - It directly targets the bacteria in the gastrointestinal tract, making it superior to IV antibiotics for localized gut infections. *IV metronidazole* - While **IV metronidazole** was previously used for severe CDI, its efficacy is inferior to oral vancomycin, especially in severe cases, because it does not achieve high enough luminal concentrations. - It is often reserved for circumstances where oral administration is not possible or in combination with oral vancomycin for critically ill patients. *IV ciprofloxacin* - **IV ciprofloxacin** is a fluoroquinolone antibiotic and is **not effective** against *C. difficile*; in fact, fluoroquinolones are a common risk factor for developing CDI [1]. - Using ciprofloxacin would exacerbate the infection rather than treat it. *Oral doxycycline* - **Oral doxycycline** is a tetracycline antibiotic and has **no established efficacy** against *Clostridium difficile* infection. - It would not be an appropriate treatment and could potentially worsen the patient's condition by disrupting the gut microbiome further.

Q: A 30-year-old patient presents with a dry cough, fever, and myalgia. Chest X-ray shows bilateral ground-glass opacities. What is the most likely diagnosis?

Viral pneumonia. ***Viral pneumonia*** - The constellation of **dry cough**, fever, myalgia, and **bilateral ground-glass opacities** on Chest X-ray is highly suggestive of viral pneumonia. - Typical pathogens include **influenza**, **RSV**, and **SARS-CoV-2**, which often lead to diffuse lung involvement. *Mycoplasma pneumonia* - While it causes **dry cough** and fever, Mycoplasma pneumonia typically presents with **patchy infiltrates** on CXR, rather than ground-glass opacities. - Mycoplasma infections are often milder and can be referred to as "walking pneumonia." *Pulmonary embolism* - Characterized by **sudden onset dyspnea**, pleuritic chest pain, and sometimes hemoptysis, which are not the primary symptoms here. - CXR findings in pulmonary embolism are often normal or show nonspecific findings like **Westermark sign** or **Hampton's hump**, not ground-glass opacities. *Tuberculosis* - Typically presents with **chronic cough**, weight loss, night sweats, and **hemoptysis**. - Chest X-ray usually shows **cavitary lesions**, infiltrates in the upper lobes, or **miliary patterns**, which differ from ground-glass opacities.

Q: A patient presents with hemoptysis, weight loss, and fatigue. Chest X-ray shows cavitary lesions in the upper lobes. What is the most likely diagnosis?

Tuberculosis. ### Tuberculosis - The combination of **hemoptysis**, **weight loss**, and **fatigue** is highly suggestive of active pulmonary tuberculosis [1, 2]. - **Cavitary lesions** in the **upper lobes** on chest X-ray are a classic radiographic finding for post-primary (reactivation) tuberculosis [3]. ### Lung abscess - While it can cause **hemoptysis** and **fatigue**, weight loss is less prominent unless chronic, and abscesses are typically solitary and may be located anywhere in the lung, not exclusively upper lobes [1]. - Lung abscesses are often associated with **fever**, **purulent sputum**, and a history of **aspiration**, which are not mentioned. ### Pulmonary embolism - Symptoms usually include **acute dyspnea**, **chest pain**, and sometimes **hemoptysis**, but **weight loss** and **fatigue** are not typical chronic symptoms [1]. - Chest X-rays in pulmonary embolism usually show **normal findings** or **non-specific changes** like a Westermark sign or Hampton hump, not cavitations. ### Bronchiectasis - Characterized by **chronic cough with copious purulent sputum** and recurrent infections, leading to **dilated bronchi**. - While **hemoptysis** can occur due to bronchial artery erosion, **weight loss** is less common, and chest X-rays typically show **"tram-track" opacities** or **cystic changes**, not cavitations as the primary finding [1].

Q: A 35-year-old woman presents with facial pain, nasal congestion, and purulent nasal discharge for 10 days. What is the most likely diagnosis?

Acute sinusitis. ***Acute sinusitis*** - The combination of **facial pain**, **nasal congestion**, and **purulent nasal discharge** for 10 days is highly characteristic of acute sinusitis, indicating inflammation and infection of the paranasal sinuses. - The persistence of symptoms for over 7-10 days, or worsening symptoms after initial improvement, supports a bacterial etiology rather than a self-limiting viral infection. *Migraine* - Migraines typically present with **unilateral, throbbing headache**, often accompanied by **photophobia, phonophobia**, and nausea, without purulent nasal discharge [1]. - While facial pain can occur, it's usually not associated with nasal congestion or discharge [1]. *Tension headache* - Tension headaches are usually characterized by **bilateral, pressing or tightening pain**, often described as a band around the head, and are not associated with nasal symptoms or purulent discharge [1]. - They typically lack the other features of sinusitis or migraines. *Trigeminal neuralgia* - This condition involves **sudden, severe, brief, stabbing or shock-like pain** in the distribution of the trigeminal nerve, often triggered by light touch or movement. - It does not present with nasal congestion or purulent discharge.

Q: A 25-year-old woman presents with a sudden onset of high fever, chills, and rigors. Blood cultures are pending. What is the next appropriate step in her management?

Administer broad-spectrum antibiotics. ***Administer broad-spectrum antibiotics*** - The patient presents with classic signs of **sepsis** (high fever, chills, rigors), which is a medical emergency requiring prompt intervention [2]. - **Early administration of broad-spectrum antibiotics** is crucial to improve outcomes and reduce mortality in suspected sepsis, even before culture results are available [1]. *Wait for blood culture results* - Delaying antibiotic treatment in a patient with suspected sepsis can lead to rapid clinical deterioration and increased mortality [1]. - While blood cultures are essential to guide definitive therapy, initial empiric broad-spectrum antibiotics should not be withheld [3]. *Start antipyretic therapy only* - Antipyretics only address the symptom of fever and do not treat the underlying infection causing the fever and chills. - This approach would leave the potentially life-threatening infection untreated, leading to worsening patient condition. *Order a CT scan* - A CT scan is not the immediate priority in a patient presenting with acute signs of systemic infection and suspected sepsis. - While it may be useful later to identify a source of infection, controlling the infection with antibiotics is the most urgent step.

Q: A 35-year-old male presents with fever, night sweats, and unintentional weight loss over the past 3 months. He has a history of intravenous drug use. Most appropriate next step in the diagnosis?

HIV test. ***HIV test*** - The patient's **risk factors** (intravenous drug use) and constitutional symptoms (fever, night sweats, unintentional weight loss) are highly suggestive of **HIV infection**, [2], [5] which can lead to opportunistic infections or directly cause these symptoms. - An HIV test is crucial for **early diagnosis** and management to prevent progression to AIDS and initiate highly active antiretroviral therapy (HAART) [4]. *Chest X-ray* - While a Chest X-ray can detect pulmonary infections often associated with immunosuppression, it is a **secondary investigation** and not the most appropriate initial diagnostic step for the underlying cause of immunosuppression. - It would be more useful after identifying an underlying condition like HIV, especially if respiratory symptoms were prominent. *Tuberculin skin test* - Tuberculosis is a common opportunistic infection in immunocompromised individuals, including those with HIV, and can present with these symptoms [1]. - However, performing a **Tuberculin skin test** or **IGRA** is typically done after initial screening for HIV, as the interpretation relies on the patient's immune status. *Blood culture* - Blood cultures are useful for detecting **bacteremia or fungemia** and can help identify specific infections [3]. - While relevant for fever and night sweats, they are a **specific diagnostic test** for active bloodstream infection and do not address the underlying systemic cause of immunosuppression and constitutional symptoms like HIV.

Q: Which of the following diseases does not typically present with fever, rash, and lymphadenopathy?

Rheumatic fever. ### Original Explanation ***Rheumatic fever*** - While **fever** can be present, rheumatic fever is primarily characterized by migratory polyarthritis, carditis, chorea, erythema marginatum, and subcutaneous nodules, with a **rash (erythema marginatum)** being less common and not often accompanied by significant **lymphadenopathy** [1]. - Its etiology is linked to a prior **Streptococcus pyogenes infection** [1]. *Toxoplasmosis* - **Fever**, widespread **lymphadenopathy**, and a **maculopapular rash** are common features in acute toxoplasmosis, particularly in immunocompromised individuals. - Ocular and neurological involvement can also occur, distinguishing it from other conditions. *Rubella* - Known as **German measles**, it typically presents with a **low-grade fever**, a characteristic **maculopapular rash** that starts on the face and spreads downwards, and prominent **postauricular and occipital lymphadenopathy**. - It is a milder disease than measles but has significant implications during pregnancy. *Measles* - Characterized by **high fever**, a **maculopapular rash** that begins on the face and spreads, and significant **lymphadenopathy**, along with cough, coryza, and conjunctivitis (the "3 Cs") [2]. - **Koplik spots** on the buccal mucosa are pathognomonic for measles [2].

Question 1

A 50-year-old farmer presents with cough, fever, and weight loss. CXR shows upper lobe cavitary lesions. Sputum culture reveals acid-fast bacilli resistant to isoniazid and rifampin. What is the next best drug?

Accepted Answer

Fluoroquinolone

Answer

Linezolid

Answer

Ethambutol

Answer

Pyrazinamide

Question 2

A 45-year-old male presents with fever, cough, and cavitary lesion on CXR. What is the most likely diagnosis?

Accepted Answer

TB

Answer

Sarcoidosis

Answer

Lung cancer

Answer

Lung abscess

Question 3

A 45-year-old HIV-positive man presents with fever and cough. Sputum culture shows acid-fast bacilli. Which of the following drugs is essential in the treatment regimen?

Accepted Answer

Isoniazid

Answer

Doxycycline

Answer

Amoxicillin

Answer

Ciprofloxacin

Question 4

A 40-year-old patient presents with frequent watery diarrhea after a recent course of antibiotics. Stool toxin assay is positive for Clostridium difficile. What is the most appropriate treatment?

Accepted Answer

Oral vancomycin

Answer

IV metronidazole

Answer

IV ciprofloxacin

Answer

Oral doxycycline

Question 5

A 30-year-old patient presents with a dry cough, fever, and myalgia. Chest X-ray shows bilateral ground-glass opacities. What is the most likely diagnosis?

Accepted Answer

Viral pneumonia

Answer

Mycoplasma pneumonia

Answer

Pulmonary embolism

Answer

Tuberculosis

Question 6

A patient presents with hemoptysis, weight loss, and fatigue. Chest X-ray shows cavitary lesions in the upper lobes. What is the most likely diagnosis?

Accepted Answer

Tuberculosis

Answer

Lung abscess

Answer

Pulmonary embolism

Answer

Bronchiectasis

Question 7

A 35-year-old woman presents with facial pain, nasal congestion, and purulent nasal discharge for 10 days. What is the most likely diagnosis?

Accepted Answer

Acute sinusitis

Answer

Migraine

Answer

Tension headache

Answer

Trigeminal neuralgia

Question 8

A 25-year-old woman presents with a sudden onset of high fever, chills, and rigors. Blood cultures are pending. What is the next appropriate step in her management?

Accepted Answer

Administer broad-spectrum antibiotics

Answer

Wait for blood culture results

Answer

Start antipyretic therapy only

Answer

Order a CT scan

Question 9

A 35-year-old male presents with fever, night sweats, and unintentional weight loss over the past 3 months. He has a history of intravenous drug use. Most appropriate next step in the diagnosis?

Accepted Answer

HIV test

Answer

Chest X-ray

Answer

Tuberculin skin test

Answer

Blood culture

Question 10

Which of the following diseases does not typically present with fever, rash, and lymphadenopathy?

Accepted Answer

Rheumatic fever

Answer

Toxoplasmosis

Answer

Rubella

Answer

Measles

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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