RESPIRATORY

Pneumonias

Typical vs atypical. CAP vs HAP. The organisms, the x-rays, the board traps. Every vignette starts with a cough.
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Before you scroll: which is it?
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A 72-year-old nursing home resident develops fever, productive cough with rusty sputum, and rigors. CXR shows lobar consolidation. Which organism?

Nice. S. pneumoniae is the #1 cause of CAP in every age group. Rusty sputum + lobar consolidation + rigors = classic pneumococcal presentation. This vignette is a gift on boards.
Good instinct, but rusty sputum + lobar consolidation + rigors = the textbook S. pneumoniae vignette. Klebsiella gives currant jelly sputum and hits alcoholics. Mycoplasma is walking pneumonia in young adults. Legionella comes from water sources with GI symptoms.
1
Typical vs Atypical — The Split
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Every pneumonia vignette is asking you one question first: typical or atypical? Get this right and you're halfway to the answer.

TYPICAL

  • Sudden onset — "woke up with 103F"
  • Productive cough — sputum you can describe
  • Lobar consolidation on CXR
  • High fever + rigors
  • Elevated WBC with left shift
  • Bacteria: S. pneumo, H. flu, Moraxella, Klebsiella, S. aureus

ATYPICAL

  • Gradual onset — "getting worse for a week"
  • Dry, nonproductive cough
  • Diffuse interstitial infiltrates on CXR
  • Low-grade fever, constitutional symptoms
  • WBC may be normal
  • Bugs: Mycoplasma, Chlamydophila, Legionella, viruses
A 22-year-old college student has had a dry cough for 10 days with low-grade fever. CXR shows bilateral patchy infiltrates that look "worse than the patient." Typical or atypical?
Yes. The "X-ray looks worse than the patient" line is basically code for atypical pneumonia. Young patient, gradual onset, dry cough, bilateral infiltrates = Mycoplasma until proven otherwise.
This is classic atypical. The tell: "X-ray looks worse than the patient." That phrase appears on boards specifically to signal atypical pneumonia. Gradual onset + dry cough + young adult + bilateral infiltrates = Mycoplasma.

🔑 Memory hook Typical is LOUD — high fever, productive cough, one lobe lights up. Atypical is QUIET — low fever, dry cough, hazy everywhere. Loud bugs are bacterial bullies. Quiet bugs sneak in.

2
The Bug Lineup
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Each organism has a signature vignette. Boards test the signature, not the exception.

S. pneumoniae

  • Rusty sputum
  • #1 cause of CAP — all ages
  • Lobar consolidation
  • Lancet-shaped gram+ diplococci
  • Optochin sensitive

Mycoplasma

  • Walking pneumonia
  • Young adults, dorms, military
  • X-ray worse than patient
  • No cell wall — beta-lactams useless
  • Cold agglutinins (IgM vs RBCs)

Klebsiella

  • Currant jelly sputum
  • Alcoholics, homeless
  • Upper lobe cavitation
  • Gram-negative rod, mucoid capsule
  • Necrotizing — tissue destruction

Legionella

  • GI symptoms + pneumonia
  • Water source: AC, cruise ship, hotel
  • High fever + relative bradycardia
  • Hyponatremia on labs
  • Silver stain or urinary antigen

S. aureus

  • Post-influenza pneumonia
  • Rapid cavitation
  • Bilateral infiltrates, very sick
  • "Had the flu, got better, then crashed"
  • Think MRSA if healthcare-associated

Pseudomonas

  • CF + ventilator + burns
  • Hospital-acquired, ICU
  • Green sputum, fruity smell
  • Needs double coverage
  • Gram-negative rod, oxidase+

PCP (Pneumocystis)

  • HIV + CD4 < 200
  • Bilateral ground-glass on CT
  • Elevated LDH
  • TMP-SMX treatment + prophylaxis
  • Add steroids if PaO2 < 70

Chlamydophila

  • Hoarseness + pharyngitis + pneumonia
  • Atypical — gradual onset
  • Often biphasic illness
  • Treat with macrolides
  • No unique lab finding

🔑 Memory hook Rusty = Pneumo (old blood, classic). Currant jelly = Klebsiella (thick, sweet, destructive). Walking = Myco (patient walks in, x-ray says they shouldn't). GI + water = Legio (cruise ship diarrhea that went to the lungs).

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Sort the Clues
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Drag each clinical finding to the correct organism. Wrong answers bounce back.

Rusty sputum
Currant jelly
Cold agglutinins
Hyponatremia
Post-influenza crash
CD4 < 200
Hotel water tower
Alcoholic + upper lobe cavity
X-ray worse than patient
Lancet-shaped diplococci
CF exacerbation
Bilateral ground-glass

S. pneumoniae

Mycoplasma

Klebsiella

Legionella

S. aureus

PCP

Pseudomonas

4
CAP Treatment — The Algorithm
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Treatment depends on ONE question: outpatient, inpatient floor, or ICU?

Where is this patient being treated?
This determines your antibiotic choice.
Outpatient, Healthy

Amoxicillin (typical coverage) OR

Doxycycline (covers typical + atypical) OR

Macrolide (azithromycin) — only if local resistance < 25%

Why not azithromycin first? Resistance. Boards will test this.

Outpatient, Comorbidities

Comorbidities = broader coverage needed

Respiratory fluoroquinolone (levofloxacin, moxifloxacin) OR

Amoxicillin-clavulanate + macrolide

The fluoroquinolone covers both typical AND atypical in one pill. That's why it's preferred for comorbid patients.

Inpatient Floor

Respiratory fluoroquinolone alone OR

Beta-lactam + macrolide (ceftriaxone + azithromycin)

The ceftriaxone + azithromycin combo is the most tested combination on boards. Ceftriaxone for typical organisms, azithromycin for atypical coverage.

ICU

Beta-lactam + macrolide (minimum) OR

Beta-lactam + respiratory fluoroquinolone

If Pseudomonas risk: anti-pseudomonal beta-lactam (piperacillin-tazobactam, cefepime, or meropenem) + fluoroquinolone

If MRSA risk: add vancomycin or linezolid

ICU = never monotherapy. Board trap: student picks levofloxacin alone for ICU patient. Wrong.

🔑 Memory hook Outpatient healthy = simple (amoxicillin). Outpatient sick = fancy (fluoroquinolone). Inpatient = combo meal (ceftriaxone + azithro). ICU = everything on the menu. Escalation ladder: sicker patient = more drugs.

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Board Traps
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Trap #1: "Got better then got worse"

Patient had influenza, improved, then rapidly deteriorated with high fever and bilateral infiltrates. This is post-influenza S. aureus pneumonia. The "biphasic illness" is the giveaway.

Trap #2: Alcoholic with pneumonia

If the sputum is currant jelly and there's upper lobe cavitation = Klebsiella. But the #1 cause of pneumonia in alcoholics is still S. pneumoniae. Boards test both — read the sputum description.

Trap #3: Ventilator pneumonia timing

Early VAP (< 5 days) = normal bugs (S. pneumo, H. flu, MSSA). Treat narrow.
Late VAP (> 5 days) = MDR bugs (Pseudomonas, Acinetobacter, MRSA). Treat wide.

Trap #4: Pneumonia + diarrhea

If the vignette mentions GI symptoms alongside pneumonia — especially with a water source (hotel, cruise, AC unit) and hyponatremia — it's Legionella. Not just an atypical pneumonia. THE atypical pneumonia with GI involvement.

Trap #5: Cystic fibrosis pneumonia

First infection in CF kids: S. aureus. Chronic colonizer in CF adults: Pseudomonas. They will give you a CF patient's age to see if you know which one to pick.

Trap #6: PCP prophylaxis threshold

CD4 < 200 = start TMP-SMX prophylaxis. The patient doesn't have PCP yet — the question is asking when to start prevention. If PaO2 < 70 during active PCP, add steroids.

A patient on a ventilator for 8 days develops fever and new infiltrates. Gram stain shows gram-negative rods. What is the most appropriate empiric therapy?
Yes. Late VAP (> 5 days) = assume MDR organisms. You need anti-pseudomonal + MRSA coverage. Ceftriaxone + azithro is the inpatient CAP combo — wrong setting. Monotherapy is never enough for late VAP.
Late VAP (> 5 days on ventilator) = MDR organisms. Need broad coverage: anti-pseudomonal beta-lactam + fluoroquinolone + vancomycin. Ceftriaxone + azithro is for CAP on the floor. Monotherapy won't cut it here.
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Elimination Game
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Clinical clues appear one at a time. After each clue, tap the organism you think it is. Fewer clues = better instinct.

TEST YOURSELF

Board-Style Questions

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