INFECTIOUS DISEASES EXAM | 2026 UPDATE
WITH COMPLETE SOLUTIONS.
SECTION 1: BACTERIAL INFECTIONS – RESPIRATORY
1. A 65-year-old man with a 40 pack-year smoking history presents with fever,
productive cough with green sputum, and pleuritic chest pain. Chest X-ray shows
a right lower lobe infiltrate. What is the most likely causative organism?
• A) Streptococcus pneumoniae
• B) Mycoplasma pneumoniae
• C) Haemophilus influenzae
• D) Legionella pneumophila
Correct Answer: A
*Rationale: Streptococcus pneumoniae is the most common cause of community-
acquired pneumonia (CAP) in all age groups. Classic presentation includes fever,
productive cough, and pleuritic chest pain. Mycoplasma is more common in
younger patients (< 40). Legionella is associated with hyponatremia and
diarrhea.*
2. A patient with CAP is started on ceftriaxone and azithromycin. Which of the
following is the most appropriate indication for this combination?
• A) Coverage for atypical organisms (Mycoplasma, Chlamydia, Legionella)
• B) Coverage for MRSA
• C) Coverage for Pseudomonas
• D) Coverage for anaerobes
,Correct Answer: A
Rationale: The combination of a beta-lactam (ceftriaxone) plus a macrolide
(azithromycin) provides coverage for typical organisms (S. pneumoniae, H.
influenzae) and atypical organisms (Mycoplasma, Chlamydia, Legionella).
Vancomycin is added for MRSA. Piperacillin-tazobactam covers Pseudomonas.
3. A patient with CAP has a CURB-65 score of 3. What is the most appropriate
disposition?
• A) Outpatient treatment
• B) Hospital admission
• C) ICU admission
• D) Observation
Correct Answer: C
*Rationale: CURB-65 score: Confusion (1), Urea > 7 mmol/L (1), Respiratory rate ≥
30 (1), BP < 90/60 (1), Age ≥ 65 (1). Score 0-1: outpatient; 2: hospital admission; ≥
3: severe pneumonia, consider ICU admission. This patient requires ICU-level
care.*
4. A patient with COPD exacerbation presents with increased dyspnea, purulent
sputum, and fever. Which organism is most commonly responsible?
• A) Pseudomonas aeruginosa
• B) Haemophilus influenzae
• C) Staphylococcus aureus
• D) Streptococcus pneumoniae
Correct Answer: B
Rationale: Haemophilus influenzae, Streptococcus pneumoniae, and Moraxella
catarrhalis are the most common bacterial causes of acute exacerbations of COPD.
,Pseudomonas is more common in patients with severe COPD or frequent antibiotic
use.
5. A patient with pneumonia has a pleural effusion. Thoracentesis shows pH
7.10, glucose 30 mg/dL, and LDH 800 U/L. What is the most appropriate
management?
• A) Antibiotics alone
• B) Chest tube drainage
• C) Video-assisted thoracoscopic surgery (VATS)
• D) Decortication
Correct Answer: B
*Rationale: Empyema is suggested by pleural fluid pH < 7.20, glucose < 40 mg/dL,
and LDH > 1000 U/L. This requires chest tube drainage (tube thoracostomy).
VATS/decortication is needed if initial drainage fails. Antibiotics alone are
insufficient.*
6. A patient with influenza develops fever, dyspnea, and hemoptysis 5 days after
symptom onset. Chest X-ray shows bilateral infiltrates. What is the most likely
diagnosis?
• A) Bacterial superinfection (e.g., Streptococcus pneumoniae,
Staphylococcus aureus)
• B) Influenza pneumonia
• C) Pulmonary embolism
• D) ARDS
Correct Answer: A
Rationale: Influenza can be complicated by bacterial superinfection, most
commonly with Streptococcus pneumoniae or Staphylococcus aureus (including
, MRSA). Fever recurrence after improvement is a classic sign. Empiric antibiotics
should cover S. aureus and S. pneumoniae.
7. A patient with COPD and pneumonia is started on levofloxacin. Which of the
following is a side effect of fluoroquinolones?
• A) QT prolongation
• B) Tendon rupture
• C) Photosensitivity
• D) All of the above
Correct Answer: D
Rationale: Fluoroquinolones cause QT prolongation (risk of torsades de pointes),
tendon rupture (Achilles tendon), and photosensitivity. They are generally well-
tolerated but have black box warnings for tendon rupture and peripheral
neuropathy.
8. A patient with suspected tuberculosis has a positive interferon-gamma
release assay (IGRA) and a normal chest X-ray. What is the most appropriate
diagnosis?
• A) Active pulmonary tuberculosis
• B) Latent tuberculosis infection (LTBI)
• C) Extrapulmonary tuberculosis
• D) Nontuberculous mycobacterial infection
Correct Answer: B
Rationale: A positive IGRA with a normal chest X-ray and no symptoms indicates
latent TB infection (LTBI). Treatment is offered to prevent progression to active
disease. Active TB requires a positive culture or symptomatic pulmonary findings.
WITH COMPLETE SOLUTIONS.
SECTION 1: BACTERIAL INFECTIONS – RESPIRATORY
1. A 65-year-old man with a 40 pack-year smoking history presents with fever,
productive cough with green sputum, and pleuritic chest pain. Chest X-ray shows
a right lower lobe infiltrate. What is the most likely causative organism?
• A) Streptococcus pneumoniae
• B) Mycoplasma pneumoniae
• C) Haemophilus influenzae
• D) Legionella pneumophila
Correct Answer: A
*Rationale: Streptococcus pneumoniae is the most common cause of community-
acquired pneumonia (CAP) in all age groups. Classic presentation includes fever,
productive cough, and pleuritic chest pain. Mycoplasma is more common in
younger patients (< 40). Legionella is associated with hyponatremia and
diarrhea.*
2. A patient with CAP is started on ceftriaxone and azithromycin. Which of the
following is the most appropriate indication for this combination?
• A) Coverage for atypical organisms (Mycoplasma, Chlamydia, Legionella)
• B) Coverage for MRSA
• C) Coverage for Pseudomonas
• D) Coverage for anaerobes
,Correct Answer: A
Rationale: The combination of a beta-lactam (ceftriaxone) plus a macrolide
(azithromycin) provides coverage for typical organisms (S. pneumoniae, H.
influenzae) and atypical organisms (Mycoplasma, Chlamydia, Legionella).
Vancomycin is added for MRSA. Piperacillin-tazobactam covers Pseudomonas.
3. A patient with CAP has a CURB-65 score of 3. What is the most appropriate
disposition?
• A) Outpatient treatment
• B) Hospital admission
• C) ICU admission
• D) Observation
Correct Answer: C
*Rationale: CURB-65 score: Confusion (1), Urea > 7 mmol/L (1), Respiratory rate ≥
30 (1), BP < 90/60 (1), Age ≥ 65 (1). Score 0-1: outpatient; 2: hospital admission; ≥
3: severe pneumonia, consider ICU admission. This patient requires ICU-level
care.*
4. A patient with COPD exacerbation presents with increased dyspnea, purulent
sputum, and fever. Which organism is most commonly responsible?
• A) Pseudomonas aeruginosa
• B) Haemophilus influenzae
• C) Staphylococcus aureus
• D) Streptococcus pneumoniae
Correct Answer: B
Rationale: Haemophilus influenzae, Streptococcus pneumoniae, and Moraxella
catarrhalis are the most common bacterial causes of acute exacerbations of COPD.
,Pseudomonas is more common in patients with severe COPD or frequent antibiotic
use.
5. A patient with pneumonia has a pleural effusion. Thoracentesis shows pH
7.10, glucose 30 mg/dL, and LDH 800 U/L. What is the most appropriate
management?
• A) Antibiotics alone
• B) Chest tube drainage
• C) Video-assisted thoracoscopic surgery (VATS)
• D) Decortication
Correct Answer: B
*Rationale: Empyema is suggested by pleural fluid pH < 7.20, glucose < 40 mg/dL,
and LDH > 1000 U/L. This requires chest tube drainage (tube thoracostomy).
VATS/decortication is needed if initial drainage fails. Antibiotics alone are
insufficient.*
6. A patient with influenza develops fever, dyspnea, and hemoptysis 5 days after
symptom onset. Chest X-ray shows bilateral infiltrates. What is the most likely
diagnosis?
• A) Bacterial superinfection (e.g., Streptococcus pneumoniae,
Staphylococcus aureus)
• B) Influenza pneumonia
• C) Pulmonary embolism
• D) ARDS
Correct Answer: A
Rationale: Influenza can be complicated by bacterial superinfection, most
commonly with Streptococcus pneumoniae or Staphylococcus aureus (including
, MRSA). Fever recurrence after improvement is a classic sign. Empiric antibiotics
should cover S. aureus and S. pneumoniae.
7. A patient with COPD and pneumonia is started on levofloxacin. Which of the
following is a side effect of fluoroquinolones?
• A) QT prolongation
• B) Tendon rupture
• C) Photosensitivity
• D) All of the above
Correct Answer: D
Rationale: Fluoroquinolones cause QT prolongation (risk of torsades de pointes),
tendon rupture (Achilles tendon), and photosensitivity. They are generally well-
tolerated but have black box warnings for tendon rupture and peripheral
neuropathy.
8. A patient with suspected tuberculosis has a positive interferon-gamma
release assay (IGRA) and a normal chest X-ray. What is the most appropriate
diagnosis?
• A) Active pulmonary tuberculosis
• B) Latent tuberculosis infection (LTBI)
• C) Extrapulmonary tuberculosis
• D) Nontuberculous mycobacterial infection
Correct Answer: B
Rationale: A positive IGRA with a normal chest X-ray and no symptoms indicates
latent TB infection (LTBI). Treatment is offered to prevent progression to active
disease. Active TB requires a positive culture or symptomatic pulmonary findings.
