Pneumonia MCQ Answers

Q1: Typical bacterial pneumonia is caused by:

✅ Answer: D - Staphylococcus aureus

• Typical bacterial pneumonia is caused by organisms that can be identified on Gram stain and grown on standard culture media. These include S. pneumoniae, H. influenzae, Moraxella catarrhalis, S. aureus, and gram-negative rods.
• Clinical features: acute onset chills/fever, productive cough with sputum, pleuritic chest pain, dense lobar consolidation on X-ray, elevated WBC.
• Options A (Mycoplasma), B (Legionella), and C (P. carinii) are all atypical or opportunistic pathogens - they do NOT have a cell wall and cannot be Gram-stained reliably.
• S. aureus is a true typical bacterial pathogen.

Q2: An 8-year-old child with fever, productive cough, and CAP - most likely organism:

✅ Answer: C - Mycoplasma pneumoniae

• In school-age children (5-18 years), Mycoplasma pneumoniae is the most common cause of CAP, followed by S. pneumoniae and Chlamydia pneumoniae.
• H. influenzae type B is now rare due to widespread vaccination (Hib vaccine).
• Group A strep rarely causes pneumonia in this age group.
• S. aureus typically causes severe/necrotizing pneumonia, usually post-influenza, and is not the most common in this age group.

Q3: Can a 28-year-old female with atypical CAP be treated with penicillin?

✅ Answer: C - No, because penicillin is resistant to atypical CAP

• Atypical organisms (Mycoplasma, Legionella, Chlamydophila) lack a cell wall entirely or have an unusual cell wall structure. Penicillin works by inhibiting cell wall synthesis - therefore it has no effect on atypical organisms.
• Atypical CAP is treated with macrolides (e.g., azithromycin), doxycycline, or fluoroquinolones.
• Option B says "penicillin is sensitive to atypical CAP" - this is grammatically/conceptually reversed. The correct wording is that atypical organisms are resistant to (i.e., not killed by) penicillin.

Q4: All of the following can diagnose atypical CAP EXCEPT:

✅ Answer: C - Gram stain

• ESR and CRP (A): Elevated in atypical pneumonia - useful inflammatory markers. ✓
• X-rays (B): Chest radiograph shows interstitial/patchy infiltrates in atypical pneumonia (rather than lobar consolidation). ✓
• Gram stain (C): Atypical organisms (Mycoplasma, Chlamydia, Legionella) are either too small to visualize, are intracellular, or lack a cell wall - they do NOT appear on Gram stain. This is why they were historically called "atypical" - they couldn't be identified by standard microbiologic methods (Gram stain and standard culture).

Note: Option D ("All the above apply") is the distractor. The correct answer is C because Gram stain does NOT apply to atypical CAP.

Q6: A 34-year-old with dry cough, malaise, and few crackles - most likely organism:

✅ Answer: B - Mycoplasma pneumoniae

• This is the classic presentation of atypical ("walking") pneumonia:
  • Dry (non-productive) cough - not purulent
  • Malaise - gradual, subacute onset
  • Mild auscultatory findings (few crackles) - patient looks "not that sick"
  • Extrapulmonary features may include headache, sore throat, ear pain
• Mycoplasma pneumoniae is the quintessential atypical pneumonia pathogen, most common in young adults and school-age children.
• S. aureus causes a severe, fulminant presentation. E. coli and H. influenzae cause typical bacterial pneumonia with productive cough.

Q7: The above case (atypical CAP/Mycoplasma) is treated with:

✅ Answer: C - Macrolide

• Atypical CAP treatment: macrolide (e.g., azithromycin, clarithromycin), doxycycline, or fluoroquinolone.
• Penicillin (A) and Cephalosporins (B): Both are beta-lactams that target cell wall synthesis. Mycoplasma has no cell wall - these drugs are completely ineffective.
• Vancomycin (D): Also targets cell wall synthesis (gram-positive bacteria) - ineffective against Mycoplasma.
• Macrolides work by inhibiting the 50S ribosomal subunit (protein synthesis) - effective against cell wall-deficient organisms.

Q8: A 43-year-old with headache and sore throat, gradual onset - most causative agent:

✅ Answer: A - Mycoplasma pneumoniae

• Gradual/subacute onset with headache, sore throat, and eventually respiratory symptoms is classic for Mycoplasma pneumoniae.
• The key clue here is the gradual development of symptoms and the upper respiratory prodrome (sore throat, headache) - this distinguishes it from S. pneumoniae (acute, sudden onset with rigors) and Legionella (high fever, diarrhea, hyponatremia, exposure to water aerosols).
• Mycoplasma is the quintessential cause of atypical/subacute community-acquired pneumonia, especially in younger patients.

Q9: A 42-year-old shepherd with chest pain and cough - what type of pneumonia?

✅ Answer: A - CAP (Community-Acquired Pneumonia)

• CAP = pneumonia acquired outside of the hospital setting, in the community.
• A shepherd working in the community clearly has community-acquired pneumonia, not hospital-acquired (HAP) or ventilator-associated (VAP).
• Additionally, the occupational clue (shepherd) hints at a possible zoonotic atypical pathogen such as Coxiella burnetii (Q fever) - acquired from sheep, goats, and cattle - or Francisella tularensis (tularemia, from rabbits). Both cause atypical CAP.
• This is still classified as CAP regardless of the specific organism.

Summary Table