Respiratory

Community-acquired pneumonia: outpatient vs inpatient triage (CURB-65, PSI)

Clinical Overview and When to Suspect Community-Acquired Pneumonia

— 4th leading infectious cause of death in US adults; #1 infectious cause of death in adults ≥65

— ~80% managed as outpatients, but inpatient cases drive the mortality (10–12% inpatient, ~30% ICU)

— Streptococcus pneumoniae remains the most common identified bacterial pathogen; viral CAP (influenza, SARS-CoV-2, RSV) increasingly recognized as primary etiology

— Acute cough (productive or dry) + fever/chills + dyspnea or pleuritic chest pain

— Focal exam findings (crackles, bronchial breath sounds, egophony, dullness)

— Tachypnea (RR >20) and tachycardia disproportionate to fever

— In elderly: may present without fever—altered mentation, falls, decompensation of CHF/COPD, or "failure to thrive"

— Confirm pneumonia (clinical + imaging) → assess severity → choose site of care (home vs ward vs ICU) → choose empiric antibiotics → arrange follow-up

— Site-of-care decision is the most consequential initial choice—overtriage wastes resources and exposes to nosocomial harm; undertriage increases mortality

Definition: Community-acquired pneumonia (CAP) = acute lower respiratory tract infection acquired outside the hospital or within <48 hours of admission, with new radiographic infiltrate plus compatible clinical features

Epidemiology relevant to Step 3:

When to suspect CAP in clinic or ED:

Triage framework Step 3 expects you to apply:

Tools: CURB-65 (simple, bedside) and Pneumonia Severity Index/PSI (more accurate, validated, but cumbersome); IDSA/ATS 2019 minor/major criteria for ICU

Step 3 management: Severity scores supplement, never replace clinical judgment. A "low-risk" CURB-65 of 0 in a homeless patient without oral intake or a hypoxic patient with SpO₂ 89% still warrants admission. Document the score and the disposition rationale.

Board pearl: A new infiltrate on CXR is required to call it pneumonia—pure clinical diagnosis without imaging is acute bronchitis until proven otherwise, and bronchitis does not get antibiotics.

Presentation Patterns and Key History

— Abrupt onset high fever, rigors, productive cough with rust-colored or purulent sputum, pleuritic chest pain

— Single lobar consolidation on imaging

— Often preceded by viral URI (post-influenza pneumococcal or staphylococcal superinfection)

— Subacute onset, low-grade fever, dry hacking cough, prominent extrapulmonary symptoms (headache, sore throat, myalgia, GI upset)

— Mycoplasma: young adults, dorms/military barracks, bullous myringitis, cold agglutinin hemolysis

— Legionella: GI symptoms (diarrhea, abdominal pain), confusion, hyponatremia, transaminitis, relative bradycardia, exposure to contaminated water (hotels, cruise ships, hot tubs, cooling towers)

— Chlamydophila pneumoniae: hoarseness, biphasic illness

— Altered mentation, stroke/dysphagia, alcohol use, seizure, NG tube, poor dentition

— Indolent course, foul-smelling sputum, RLL or posterior segment RUL involvement, cavitation

— Recent hospitalization or IV antibiotics in prior 90 days → MRSA/Pseudomonas risk

— Structural lung disease (bronchiectasis, severe COPD, CF) → Pseudomonas

— Injection drug use, post-influenza → MRSA, S. aureus

— Travel/birds (psittacosis), rabbits (tularemia), bats/Ohio-Mississippi valley (Histoplasma), Southwest US (Coccidioides), HIV/transplant (PJP, fungal, mycobacterial)

Classic "typical" bacterial CAP (S. pneumoniae, H. influenzae, M. catarrhalis):

"Atypical" CAP (Mycoplasma, Chlamydophila, Legionella, viruses):

Aspiration risk history (anaerobes, gram-negatives):

Critical exposure and host history (drives empiric coverage):

Vaccination history: Pneumococcal (PCV20 or PCV15+PPSV23), influenza, COVID-19—influences both risk and likely pathogens

Key distinction: "Typical vs atypical" no longer reliably predicts pathogen at the bedside, but Step 3 still tests classic vignettes—Legionella with hyponatremia and diarrhea is the most testable pattern.

Board pearl: Always ask explicitly about prior 90-day antibiotic exposure and hospitalization—this single question often determines whether empiric MRSA/Pseudomonas coverage is added.

Physical Exam Findings and Hemodynamic Assessment

— Temperature: >38°C supports infection; hypothermia <36°C is an ominous severity marker (qSOFA, sepsis)

— RR >30, HR >125, SBP <90, SpO₂ <90% on room air → strongly favor inpatient care

— Always document room-air saturation before applying supplemental O₂—this is the number that drives admission

— Inspection: decreased chest excursion on affected side, accessory muscle use

— Palpation: increased tactile fremitus over consolidation

— Percussion: dullness

— Auscultation: bronchial breath sounds, late inspiratory crackles, egophony ("E-to-A" change), whispered pectoriloquy

— Pleural effusion (parapneumonic): decreased fremitus, dullness, decreased breath sounds—mandates lateral decubitus film or US

— Bullous myringitis → Mycoplasma

— Periodontal disease/edentulous → aspiration anaerobes

— Erythema multiforme/Stevens-Johnson-like rash → Mycoplasma

— Relative bradycardia (pulse-temperature dissociation) → Legionella, typhoid, viral

— qSOFA ≥2 (RR ≥22, altered mentation, SBP ≤100) or SIRS criteria → screen for sepsis, lactate, blood cultures, fluids

— Capillary refill, mottling, mental status changes—signs of hypoperfusion warrant ICU consideration regardless of CURB-65

— Confusion is one of the CURB-65 components and an independent mortality predictor, especially in elderly

— Use AMT-4 (age, DOB, place, year) or simple orientation—new confusion = "C" point

Vital signs—the triage backbone:

Pulmonary exam findings of consolidation:

Extrapulmonary clues:

Hemodynamic/sepsis assessment (do this on every CAP patient):

Mental status:

CCS pearl: On CCS cases, order vitals q1h initially, continuous pulse oximetry, and reassess exam after first dose of antibiotics and fluid—the simulator rewards iterative reassessment, not one-shot orders.

Board pearl: A hypoxic CAP patient with SpO₂ 88% on RA but CURB-65 of 1 still needs admission—hypoxemia trumps the score.

Diagnostic Workup — Initial Labs, Imaging, and Biomarkers

— PA and lateral chest radiograph is the standard first study; lateral view detects retrocardiac and posterior basal infiltrates

— Findings: lobar consolidation (typical bacterial), patchy/interstitial (atypical/viral), cavitation (anaerobes, S. aureus, TB, fungi), upper-lobe with volume loss (TB)

— Negative CXR does not rule out CAP in dehydrated or early-presenting patients—repeat in 24–48 h or obtain CT if suspicion is high

— Lung ultrasound: increasingly used in ED, sensitive for consolidation and effusion

— CBC with differential (leukocytosis with left shift; leukopenia is a severity marker)

— BMP (BUN for CURB-65; sodium—hyponatremia → think Legionella or SIADH; glucose for PSI)

— LFTs (transaminitis with Legionella)

— Lactate if any sepsis features

— HIV screen if not done (CDC universal screening)

— Procalcitonin: NOT used to decide whether to start antibiotics initially in CAP (false negatives early); useful for de-escalation/duration—stop antibiotics when PCT <0.25 ng/mL or drops >80%

— CRP nonspecific; not part of guideline-based triage

— Routine sputum/blood cultures NOT recommended—low yield, doesn't change empiric therapy

— Blood cultures ×2, sputum Gram stain and culture before antibiotics (do not delay antibiotics >1 h to obtain them)

— Urinary antigens for S. pneumoniae and Legionella in severe CAP, alcohol use, recent travel, or pleural effusion

— Respiratory viral PCR panel (especially influenza, SARS-CoV-2, RSV) during season

— MRSA nares swab: high NPV (~99%)—negative nares swab supports stopping empiric MRSA coverage

Chest imaging—required for diagnosis:

Pulse oximetry on room air: mandatory before any disposition decision

Labs to obtain at presentation:

Biomarkers:

Microbiology in OUTPATIENT CAP:

Microbiology in INPATIENT CAP:

Step 3 management: Order CXR + room-air SpO₂ + CBC/BMP in every suspected CAP; add cultures, urinary antigens, and viral PCR only if admitting.

Board pearl: Hyponatremia + diarrhea + transaminitis + confusion in a CAP patient = Legionella until proven otherwise—send urinary antigen.

Diagnostic Workup — Advanced or Confirmatory Studies

— Obtain when CXR is equivocal, when complications suspected (empyema, abscess, necrotizing pneumonia), or when alternate diagnosis considered (PE, malignancy, ILD)

— Contrast-enhanced CT or CT pulmonary angiogram if PE is a competing diagnosis (pleuritic pain + dyspnea + risk factors)

— Mass/post-obstructive pneumonia—non-resolving infiltrate in a smoker mandates CT and eventual bronchoscopy

— Indicated for any effusion >1 cm on lateral decubitus or US

— Send: pH, glucose, LDH, protein, cell count/differential, Gram stain, culture, cytology

— Complicated parapneumonic effusion/empyema criteria (any one): pH <7.20, glucose <40, positive Gram stain/culture, frank pus, loculations → chest tube drainage required

— Reserved for severe/ICU CAP not responding to empiric therapy, immunocompromised hosts (PJP, fungal, CMV, mycobacterial), suspected obstructing lesion

— BAL quantitative cultures, cytology, viral PCR, fungal stains, AFB, galactomannan

— Airborne isolation + 3 sputum AFB smears/cultures + NAAT if upper-lobe cavitary disease, weight loss, night sweats, hemoptysis, homelessness, incarceration, HIV, foreign-born from high-prevalence region

— Consider if S. aureus bacteremia, persistent fever, new murmur, embolic phenomena—rule out endocarditis

— Repeat CXR at 6–8 weeks in smokers >50 or those with persistent symptoms to exclude underlying malignancy

CT chest (contrast or non-contrast):

Thoracentesis for parapneumonic effusion:

Bronchoscopy with BAL:

HIV testing: all adult CAP patients per CDC; immunosuppression workup if recurrent or atypical (CD4, immunoglobulins)

TB workup:

Echocardiography:

Pulmonary function/follow-up imaging:

Key distinction: A simple parapneumonic effusion = clear, pH >7.20, glucose >60, sterile → resolves with antibiotics alone. A complicated effusion or empyema requires drainage—antibiotics alone will fail.

Board pearl: Non-resolving pneumonia in a smoker = CT chest + bronchoscopy to rule out endobronchial obstructing tumor; do not just keep changing antibiotics.

Risk Stratification and Site-of-Care Decision

— Confusion (new)

— Urea (BUN) >19 mg/dL (>7 mmol/L)

— Respiratory rate ≥30

— Blood pressure: SBP <90 or DBP ≤60

— Age ≥65

— Disposition: 0–1 → outpatient; 2 → ward (or observation); ≥3 → inpatient, consider ICU if 4–5

— Simplified CRB-65 (no BUN) usable in clinic without labs

— 20 variables (demographics, comorbidities, exam, labs, imaging)

— Stratifies into Classes I–V

— Class I–II → outpatient

— Class III → brief observation/short admission

— Class IV–V → inpatient; Class V often ICU

— More accurate than CURB-65 for identifying low-risk patients safe for outpatient management; preferred by IDSA/ATS 2019 guidelines

— Major (any 1 = ICU): septic shock requiring vasopressors; respiratory failure requiring mechanical ventilation

— Minor (≥3 = ICU): RR ≥30, PaO₂/FiO₂ ≤250, multilobar infiltrates, confusion, BUN ≥20, WBC <4, platelets <100, temp <36°C, hypotension requiring aggressive fluids

— Use PSI when available (low risk → outpatient), CURB-65 at the bedside

— Override the score and admit if: hypoxemia (SpO₂ <92% on RA), inability to take POs, unstable comorbidities, unreliable social situation (homelessness, no caregiver, no phone), failed outpatient therapy, pregnancy

— Override and discharge rarely—document reasoning

CURB-65 (each = 1 point):

Pneumonia Severity Index (PSI / Fine score):

IDSA/ATS 2019 criteria for severe CAP / ICU admission:

Step 3 management:

Board pearl: A 30-year-old with CURB-65 = 0 but SpO₂ 87% on RA, lives alone, can't tolerate POs → admit. The score is a floor, not a ceiling.

Key distinction: CURB-65 is fast and bedside; PSI is more accurate but slower. Step 3 vignettes often supply the variables for both—know which to apply.

Pharmacotherapy — Empiric Antibiotic Regimens (IDSA/ATS 2019)

— Amoxicillin 1 g PO TID (first line) OR

— Doxycycline 100 mg PO BID OR

— Macrolide (azithromycin/clarithromycin) only if local pneumococcal macrolide resistance <25% (rare in US—largely abandoned as monotherapy)

— Combination: amoxicillin/clavulanate 875/125 mg BID (or cefpodoxime/cefuroxime) PLUS macrolide or doxycycline

— OR monotherapy: respiratory fluoroquinolone (levofloxacin 750 mg, moxifloxacin 400 mg)

— β-lactam (ceftriaxone, ampicillin-sulbactam, or cefotaxime) PLUS macrolide (azithromycin)

— OR respiratory fluoroquinolone monotherapy

— β-lactam PLUS macrolide (preferred—macrolide mortality benefit in severe CAP)

— OR β-lactam plus respiratory fluoroquinolone

— Monotherapy with fluoroquinolone NOT recommended in ICU CAP

OUTPATIENT, healthy, no comorbidities, no prior antibiotic exposure:

OUTPATIENT with comorbidities (chronic heart/lung/liver/renal disease, DM, alcohol use, malignancy, asplenia) or recent antibiotics:

INPATIENT, non-severe (ward):

INPATIENT, severe (ICU):

Add MRSA coverage (vancomycin or linezolid) if: prior MRSA isolate, prior IV antibiotics in 90 days + locally validated risk, necrotizing/cavitary pneumonia, post-influenza, severe CAP with risk factors

Add Pseudomonas coverage (piperacillin-tazobactam, cefepime, meropenem, or levofloxacin) if: prior Pseudomonas, structural lung disease, recent IV antibiotics + hospitalization

De-escalate at 48 h based on cultures, negative MRSA nares (NPV ~99%), and clinical response

Influenza co-infection: add oseltamivir for any inpatient with influenza regardless of symptom duration

Duration: minimum 5 days, continue until afebrile 48 h and clinically stable; longer (7–14 d) for MRSA, Pseudomonas, complications

Step 3 management: First antibiotic dose within 1 hour for septic patients, within 4 hours for stable inpatients—do not delay for cultures.

Board pearl: Fluoroquinolones can mask undiagnosed TB and select resistance—avoid empiric fluoroquinolones if TB is on the differential (cavitary, weight loss, high-risk demographics).

Adjunctive Management and Supportive Care

— Target SpO₂ 92–96% (88–92% if CO₂ retainer/COPD)

— Escalation: nasal cannula → high-flow nasal cannula (HFNC) → NIV (consider in selected, but high failure rate in pneumonia) → intubation

— HFNC preferred over NIV in hypoxemic respiratory failure from CAP (FLORALI trial)

— 30 mL/kg balanced crystalloid within 3 h for sepsis-induced hypoperfusion or lactate ≥4

— Reassess volume status (POCUS, passive leg raise, dynamic indices) before continued boluses—avoid fluid overload

— Hydrocortisone 200 mg/day IV ×7 days (or methylprednisolone) reduces mortality in severe CAP requiring ICU (CAPE COD trial, 2023)

— Not routinely recommended for non-severe CAP

— Avoid in influenza pneumonia (worse outcomes) and uncontrolled diabetes unless compelling indication

— Oseltamivir 75 mg BID ×5 days for any hospitalized influenza-positive patient

— SARS-CoV-2: per current protocols (remdesivir, dexamethasone if hypoxemic, etc.)

— Empyema or complicated parapneumonic effusion → chest tube ± intrapleural tPA/DNase (MIST-2)

— Lung abscess: usually responds to prolonged antibiotics; surgical drainage if >6 cm, failure, or hemorrhage

Oxygen therapy:

Fluid resuscitation:

Vasopressors: norepinephrine first-line if MAP <65 after fluids; add vasopressin if escalating

Corticosteroids:

VTE prophylaxis: all admitted CAP patients—enoxaparin 40 mg SC daily or heparin 5000 U SC q8h unless contraindicated

Glycemic control, nutrition, early mobilization, aspiration precautions

Antiviral therapy:

Drainage of complications:

Transition IV→PO antibiotics: when hemodynamically stable, afebrile or improving, tolerating POs, GI absorption intact—usually by day 2–3

CCS pearl: On CCS, order continuous pulse oximetry, IV fluids, empiric antibiotics, blood cultures (before antibiotics), oxygen, and DVT prophylaxis as a bundle in the first virtual hour, then advance the clock and reassess vitals/labs.

Board pearl: In severe CAP with septic shock, adding low-dose hydrocortisone is now a guideline-supported, mortality-reducing intervention—a frequent Step 3 update item.

Special Populations — Elderly and Renal/Hepatic Impairment

— Atypical presentation: delirium, falls, anorexia, generalized weakness, decompensated CHF/COPD—fever may be absent in up to 30%

— Aspiration risk from dysphagia (post-stroke), dementia, sedating medications—favor amoxicillin-clavulanate for anaerobic coverage when aspiration suspected

— Higher PSI scores → almost always admitted; nursing-home residents need additional MRSA/Pseudomonas risk assessment

— Avoid fluoroquinolones when possible: QT prolongation, tendon rupture (especially with steroids), C. difficile, delirium, hypoglycemia

— Macrolides: QT prolongation, drug interactions (warfarin, statins, CYP3A4)

— Vaccination check: PCV20 alone OR PCV15 followed by PPSV23 for all adults ≥65; annual influenza; COVID-19; RSV vaccine (≥75 or 60–74 with risk factors, shared decision)

— Dose adjust: levofloxacin (CrCl <50), ciprofloxacin, β-lactams (cefepime, piperacillin-tazobactam), vancomycin (AUC-based or trough), TMP-SMX, acyclovir

— No adjustment needed: azithromycin, doxycycline, ceftriaxone, moxifloxacin, linezolid

— Cefepime neurotoxicity (encephalopathy, myoclonus, non-convulsive seizures) in renal failure—dose-reduce and recognize

— Avoid nephrotoxin stacking (vancomycin + piperacillin-tazobactam + contrast)

— Avoid/reduce: tigecycline, prolonged azithromycin, high-dose acetaminophen

— Moxifloxacin: hepatotoxicity risk

— Ceftriaxone: biliary sludging (caution in cirrhosis with biliary disease)

— Discuss code status and goals on admission—pneumonia is a common terminal event in advanced dementia and frailty; aggressive antibiotics may not align with goals

Elderly (≥65):

Renal impairment:

Hepatic impairment:

Frailty and goals of care:

Step 3 management: In any elderly CAP patient, screen for aspiration (bedside swallow eval), review the med list for sedating/anticholinergic drugs, and update vaccinations before discharge.

Board pearl: New confusion in an elderly patient with a normal-temperature exam may be the only sign of pneumonia—always image the chest in unexplained delirium with leukocytosis or hypoxemia.

Special Populations — Pregnancy, Pediatrics, Immunocompromised

— Increased mortality and complications (preterm labor, low birth weight); admit with a lower threshold

— Safe antibiotics: β-lactams (amoxicillin, amoxicillin-clavulanate, ceftriaxone), azithromycin

— Avoid: doxycycline (tooth/bone effects, 2nd–3rd trimester), fluoroquinolones (cartilage—use only if no alternative), TMP-SMX (1st trimester neural tube; 3rd trimester kernicterus)

— Influenza in pregnancy: high mortality—oseltamivir promptly regardless of trimester

— Vaccinate: inactivated influenza (any trimester), Tdap (27–36 wk), COVID-19, RSV (32–36 wk seasonally)

— Outpatient first-line: high-dose amoxicillin for typical bacterial CAP

— School-age with atypical features: add or use azithromycin for Mycoplasma

— Admit if hypoxia, dehydration, <6 months, toxic appearance, failed outpatient therapy

— CD4 <200: Pneumocystis jirovecii (PJP)—bilateral interstitial infiltrates, hypoxia disproportionate to CXR, elevated LDH; treat with TMP-SMX + steroids if PaO₂ <70 or A-a gradient >35

— CD4 <100: also consider CMV, fungal, MAC

— Always test for HIV in adults with CAP

— Broad-spectrum (cefepime or piperacillin-tazobactam) ± vancomycin

— Consider fungal (Aspergillus → halo sign on CT, galactomannan) and viral pathogens

— G-CSF if prolonged neutropenia

— Expanded differential: PJP, CMV, fungal, Nocardia, mycobacterial—low threshold for CT and bronchoscopy

— Risk of overwhelming encapsulated organisms (S. pneumoniae, H. influenzae, N. meningitidis)—ensure vaccinations and consider standby antibiotics

Pregnancy:

Pediatrics (Step 3 still tests adult medicine peds crossover):

HIV/AIDS:

Neutropenia (ANC <500):

Solid organ/HSCT transplant, biologics (anti-TNF, rituximab, JAK inhibitors):

Asplenia (functional or anatomic):

Key distinction: PJP vs bacterial CAP—PJP gives diffuse bilateral ground-glass on CT, profound hypoxia, often dry cough, in HIV/transplant; bacterial CAP gives lobar consolidation and productive cough.

Step 3 management: In any pregnant patient with CAP, admit if hypoxemia, multilobar disease, or severe symptoms; coordinate with obstetrics for fetal monitoring.

Complications and Adverse Outcomes

— Parapneumonic effusion (40% of admitted CAP)—most simple, resolve with antibiotics

— Complicated parapneumonic effusion / empyema: pH <7.20, glucose <40, positive Gram stain/culture, loculations, frank pus → chest tube drainage + intrapleural tPA/DNase if loculated; VATS if failure

— Lung abscess: cavitary lesion with air-fluid level; usually anaerobic/aspiration; treat with prolonged antibiotics (4–6 weeks ampicillin-sulbactam or clindamycin); drainage rarely needed

— Necrotizing pneumonia: S. aureus (especially MRSA with PVL toxin), Klebsiella, anaerobes—often requires extended therapy ± surgical resection

— ARDS: bilateral infiltrates, PaO₂/FiO₂ <300, non-cardiogenic—lung-protective ventilation (6 mL/kg, plateau <30, PEEP titration, prone positioning if severe)

— Respiratory failure requiring mechanical ventilation

— Acute MI, atrial fibrillation, decompensated heart failure—CAP triples short-term cardiovascular event risk; check troponin and ECG if chest pain or dyspnea disproportionate

— Pneumococcal pneumonia has direct myocardial invasion potential

— Sepsis/septic shock, AKI, hepatic dysfunction, DIC

— Metastatic infection: meningitis (pneumococcal), endocarditis (S. aureus, pneumococcal—Austrian syndrome = pneumonia + meningitis + endocarditis), septic arthritis

— C. difficile colitis (fluoroquinolones, clindamycin highest risk)

— QT prolongation, tendon rupture, aortic aneurysm/dissection (fluoroquinolones)

— AKI (vancomycin + piperacillin-tazobactam combination)

— 1-year mortality after CAP hospitalization is ~30% in elderly—largely cardiovascular

— Functional decline, post-ICU syndrome

Pulmonary complications:

Cardiovascular complications (often missed on Step 3):

Septic complications:

Pharmacologic complications:

Long-term outcomes:

Non-resolving pneumonia: failure to improve in 72 h or radiographic resolution in 4 weeks → reassess for resistant pathogens, complications (empyema, abscess), wrong diagnosis (PE, malignancy, vasculitis, organizing pneumonia)

Board pearl: Austrian syndrome (pneumococcal pneumonia + meningitis + endocarditis) classically occurs in alcohol use disorder—do an echo and LP if clinical features fit.

When to Escalate Care — ICU, Consults, Inpatient Triage

— Major (any one = ICU): septic shock requiring vasopressors after fluid resuscitation; respiratory failure requiring mechanical ventilation (invasive or sustained NIV/HFNC failure)

— Minor (≥3 = ICU): RR ≥30, PaO₂/FiO₂ ≤250, multilobar infiltrates, confusion/disorientation, BUN ≥20, WBC <4, platelets <100, temp <36°C, hypotension requiring aggressive fluids

— Rising lactate despite resuscitation

— Worsening hypoxemia on increasing oxygen requirements

— New AKI, hepatic dysfunction, coagulopathy

— Cardiac complications (new arrhythmia, MI, decompensated HF)

— Failure to respond to initial antibiotics in 72 h with clinical deterioration

— Inability to maintain SpO₂ >90% on >6 L NC

— Pulmonology: non-resolving pneumonia, need for bronchoscopy, suspected obstructing lesion, complex effusion

— Infectious disease: severe CAP, immunocompromised, suspected MDR organism, unusual pathogens, treatment failure, prolonged duration

— Thoracic surgery / interventional pulmonology: empyema needing drainage or VATS, lung abscess, persistent air leak

— Critical care: any severe CAP meeting ICU criteria

— A patient meets ward criteria but lives alone with no caregiver and altered mentation → admit, do not discharge with "follow up tomorrow"

— A patient meets outpatient criteria but cannot afford or obtain antibiotics → observation unit or admit briefly to ensure first doses

— Severe CAP in advanced dementia/frailty/end-stage organ disease → early palliative care consult, clarify code status, discuss time-limited trials of life support

ICU admission triggers (IDSA/ATS 2019):

Other escalation indicators:

Ward → step-down/ICU transfer:

Consult triggers:

Inpatient triage decision points Step 3 loves:

Goals-of-care escalation:

CCS pearl: On the simulator, moving a patient to ICU is a one-click order—don't hesitate when minor criteria stack up. Document repeat vitals showing the trigger.

Step 3 management: Reassess every CAP patient at 48–72 hours—if not improving, broaden workup (CT, repeat cultures, consider non-infectious mimics) before broadening antibiotics blindly.

Key Differentials — Other Infectious Lower Respiratory Causes

— Cough ± sputum, no infiltrate on CXR, normal vitals

— Almost always viral; do not give antibiotics

— Wheezing common; albuterol may help symptoms

— Abrupt fever, myalgia, headache, dry cough; can be primary viral pneumonia or precede bacterial superinfection

— Oseltamivir within 48 h (or any time if hospitalized/severe)

— Bilateral peripheral ground-glass on CT; profound hypoxemia, lymphopenia, elevated D-dimer/ferritin

— Treat with dexamethasone if hypoxemic, remdesivir, anticoagulation per protocol

— Upper-lobe cavitary, weight loss, night sweats, hemoptysis; risk factors (foreign-born, HIV, homeless, incarcerated, healthcare exposure)

— Airborne isolation immediately, AFB ×3 + NAAT

— Pneumonitis = chemical injury from gastric acid, occurs hours after aspiration, resolves in 24–48 h without antibiotics

— Pneumonia = bacterial superinfection, develops days later, requires antibiotics (amoxicillin-clavulanate)

— Histoplasmosis (Ohio/Mississippi valleys, bats/birds)—mediastinal lymphadenopathy

— Blastomycosis (similar geography, skin lesions)

— Coccidioidomycosis (Southwest US, "Valley fever")—erythema nodosum, eosinophilia

Acute bronchitis:

Influenza:

COVID-19 pneumonia:

Tuberculosis:

Aspiration pneumonia vs aspiration pneumonitis:

Lung abscess / necrotizing pneumonia: cavitary, foul sputum, indolent

Endemic fungi:

Pneumocystis jirovecii (PJP): HIV CD4 <200, transplant, chronic steroids—bilateral interstitial, elevated LDH

Endemic zoonoses: psittacosis (birds), Q fever (livestock), tularemia (rabbits, ticks), leptospirosis

Empyema: purulent pleural fluid—requires drainage in addition to antibiotics

Bronchiectasis exacerbation: chronic productive cough, recurrent infections—often Pseudomonas

Key distinction: Aspiration pneumonitis is chemical and self-limited (no antibiotics needed unless symptoms persist >48 h or progress); aspiration pneumonia is bacterial and requires antibiotics. Step 3 tests this distinction frequently.

Board pearl: A patient with cough and clear CXR is acute bronchitis—reassure, treat symptoms, no antibiotics, document patient counseling on antibiotic stewardship.

Key Differentials — Non-Infectious Mimics

— Pleuritic chest pain, dyspnea, hypoxemia—can mimic CAP precisely

— Risk factors: malignancy, immobilization, OCPs, recent surgery, prior VTE

— CXR often normal or has Hampton's hump; D-dimer (if low pretest), CTPA confirms

— Always consider PE before settling on CAP, especially when CXR is unimpressive and hypoxemia is profound

— Bilateral infiltrates with cephalization, Kerley B lines, pleural effusions, cardiomegaly

— BNP/NT-proBNP elevated; echo for EF and diastolic function

— Often coexists with pneumonia—diurese and treat infection

— Smoker, weight loss, hemoptysis, focal wheeze, non-resolving infiltrate

— CT and bronchoscopy

— Subacute illness, patchy peripheral consolidations, no response to antibiotics, dramatic response to corticosteroids

— Acute or chronic; peripheral eosinophilia (chronic form); responds to steroids

— Exposure history (birds, molds, hot tubs), centrilobular nodules on CT

— GPA (Wegener's): cavitary nodules, hemoptysis, c-ANCA, renal involvement

— Eosinophilic GPA (Churg-Strauss): asthma, eosinophilia, p-ANCA

— Diffuse alveolar hemorrhage

— Amiodarone, methotrexate, nitrofurantoin, bleomycin, immune checkpoint inhibitors

— Rapidly progressive bilateral infiltrates resembling ARDS without identified cause

Pulmonary embolism:

Acute decompensated heart failure / cardiogenic pulmonary edema:

Lung malignancy / post-obstructive pneumonia:

Cryptogenic organizing pneumonia (COP):

Eosinophilic pneumonia:

Hypersensitivity pneumonitis:

Pulmonary vasculitis:

Drug-induced pneumonitis:

Acute interstitial pneumonia / AIP:

Pulmonary infarction, contusion, atelectasis, radiation pneumonitis

Key distinction: Non-resolving pneumonia at 4 weeks = expand differential beyond infection—CT chest, bronchoscopy, autoimmune workup (ANCA, ANA), consider COP/eosinophilic/vasculitis.

Board pearl: Bilateral lower-lobe pneumonia on a smoker on amiodarone that doesn't respond to antibiotics → think amiodarone pulmonary toxicity; hold drug, consider steroids.

Secondary Prevention and Discharge Plan

— Switch IV→PO when hemodynamically stable, afebrile or improving, tolerating POs

— Total duration minimum 5 days, longer for complications, MRSA, Pseudomonas (7–14 d), empyema/abscess (weeks)

— Discharge antibiotics in hand or sent to pharmacy before discharge—confirm patient can fill the prescription

— Pneumococcal: PCV20 alone, or PCV15 followed by PPSV23 ≥1 year later, for all adults ≥65 and adults 19–64 with risk factors (chronic heart/lung/liver/renal disease, DM, alcohol use, smoking, immunocompromise, CSF leak, cochlear implant, asplenia)

— Influenza: annual, all adults

— COVID-19: per current ACIP recommendations

— RSV: adults ≥75; 60–74 with risk factors (shared decision)

— Tdap, zoster, others as age-appropriate

— Administer before discharge—do not defer to outpatient ("missed opportunity")

— Single most important secondary prevention—counsel + offer pharmacotherapy (nicotine replacement, varenicline, bupropion)

— Hospital admission is a teachable moment with proven quit-rate benefit

— Optimize COPD (inhalers, pulmonary rehab), CHF, DM, HIV ART

— Aspiration risk: swallow eval, diet modifications, dental care

— Pulmonary rehab referral for COPD or persistent dyspnea

— Physical therapy for deconditioning

— Repeat at 6–8 weeks in smokers >50 or persistent symptoms to rule out underlying malignancy

— Not routinely needed in low-risk patients with full clinical recovery

Antibiotic transition and duration:

Vaccinations before discharge (high-yield Step 3):

Smoking cessation:

Alcohol use disorder, IV drug use: screen and refer for treatment

Manage comorbidities driving risk:

Cardiovascular risk: CAP is a CV event trigger—reinforce statin, BP, glycemic control; consider screening for occult CAD if symptoms

Functional recovery:

Follow-up CXR:

Step 3 management: Every CAP discharge order set should include: antibiotic Rx + duration, vaccines updated, smoking cessation, PCP follow-up within 1 week, return precautions, and follow-up CXR plan.

Board pearl: A common Step 3 trap: discharging a 70-year-old smoker after pneumonia without giving pneumococcal vaccine—the answer is "administer PCV20 before discharge."

Follow-Up, Monitoring, and Counseling

— Phone or in-person check within 48–72 hours of starting antibiotics

— Worsening or no improvement at 72 h → reassess in clinic, reimage, broaden workup

— Office visit within 1 week

— PCP visit within 7 days of discharge (reduces readmission)

— Medication reconciliation, confirm antibiotic adherence and completion

— Repeat vitals, SpO₂, exam; reassess for complications

— Worsening dyspnea, persistent or rising fever, hemoptysis, chest pain, confusion, inability to tolerate POs → return immediately

— Vitals q4h initially, daily weights, I/Os

— Daily exam, oxygen requirement trend

— CBC, BMP daily until improving

— Repeat CXR only if not improving or worsening—not routinely

— Stop antibiotics when PCT <0.25 ng/mL or drops >80% from peak in clinically improved patients

— Temp ≤37.8°C

— HR ≤100

— RR ≤24

— SBP ≥90

— SpO₂ ≥90% on room air (or baseline)

— Tolerating POs

— Normal mental status

— Patient can be discharged the same day they meet stability—observing an extra 24 hours doesn't reduce readmission

— Expected recovery timeline: cough may persist 2–4 weeks, fatigue weeks to months

— Complete full antibiotic course even when feeling better

— Smoking cessation resources (1-800-QUIT-NOW, varenicline)

— Vaccination plan moving forward

— Post-CAP MI/stroke risk elevated for months—reinforce ASCVD prevention

Outpatient CAP follow-up:

Inpatient CAP discharge follow-up:

Return precautions to counsel:

Monitoring parameters during inpatient stay:

Procalcitonin-guided de-escalation:

Stability criteria for discharge (Halm criteria):

Pulmonary rehab: consider for COPD, persistent dyspnea, or deconditioning

Patient counseling content:

Cardiovascular surveillance:

CCS pearl: On CCS, after discharging an inpatient CAP, schedule the 1-week follow-up appointment as an order—missing it loses points.

Board pearl: Halm criteria—a patient meeting all 7 should be discharged that day; "observe overnight just in case" is the wrong answer on Step 3.

Ethical, Legal, and Patient Safety Considerations

— Discuss code status on admission for every CAP patient, especially elderly/frail—pneumonia is a leading terminal event in advanced dementia

— Time-limited trials of mechanical ventilation can be ethically appropriate when prognosis uncertain

— Document conversations and surrogate decision-makers

— Hypoxemic or septic patients with delirium may lack decision-making capacity—identify surrogate per state hierarchy (spouse, adult children, parents, siblings)

— Capacity is decision-specific; a confused patient may still refuse a specific test but not understand discharge planning

— Thoracentesis, central line, intubation: obtain consent from surrogate if patient lacks capacity; in true emergency, implied consent applies

— Document the emergency exception clearly

— Tuberculosis, Legionella, novel influenza, SARS-CoV-2, measles, pertussis—reportable to local health department

— Failure to report is a regulatory violation; sets up contact tracing and outbreak response

— Droplet precautions for influenza, pertussis; airborne (negative pressure + N95) for suspected TB, measles, varicella, novel respiratory viruses

— Place patient in appropriate isolation before confirmatory testing returns

— Do not prescribe antibiotics for acute bronchitis or URIs—patient demand is not an indication

— De-escalate based on cultures and clinical response; document rationale

— Discharge summary to PCP within 24–48 h

— Medication reconciliation: confirm antibiotic dose, duration, interactions (warfarin + macrolide/fluoroquinolone → INR check; statin + macrolide → myopathy risk)

— Test pendings at discharge (cultures, sensitivities) must be tracked and communicated

— Confirm follow-up appointment is scheduled, not just recommended, before discharge

— Assess insurance coverage and ability to fill prescriptions; consider in-hand discharge antibiotics or social work

Goals of care and code status:

Capacity assessment:

Informed consent edge cases:

Mandatory public health reporting:

Infection control:

Antibiotic stewardship:

Transitions of care (frequent Step 3 safety theme):

Health equity:

Step 3 management: Always document who received the discharge handoff—closing the loop is the safety standard.

Board pearl: Pending blood cultures with sensitivities at discharge are a classic litigation/safety scenario—responsibility for follow-up must be explicitly assigned and communicated.

High-Yield Associations and Rapid-Fire Clinical Facts

S. pneumoniae: most common bacterial CAP; rust-colored sputum; lobar; gram-positive lancet-shaped diplococci; urinary antigen positive

H. influenzae: COPD exacerbations; gram-negative coccobacilli

M. catarrhalis: COPD; gram-negative diplococci; β-lactamase producer

Mycoplasma pneumoniae: young adults, dorms; bullous myringitis; cold agglutinin hemolysis; erythema multiforme; treat with macrolide or doxycycline (no cell wall → β-lactams useless)

Chlamydophila pneumoniae: hoarseness, biphasic illness

Legionella pneumophila: water sources (hotels, cruise ships, cooling towers); GI symptoms, confusion, hyponatremia, transaminitis, relative bradycardia; urinary antigen detects serogroup 1 (most cases); treat with macrolide or fluoroquinolone

Klebsiella pneumoniae: alcohol use, diabetes; currant jelly sputum; upper-lobe; bulging fissure sign; cavitation

Pseudomonas aeruginosa: structural lung disease (bronchiectasis, CF, severe COPD), recent hospitalization

Staphylococcus aureus / MRSA: post-influenza, IVDU, necrotizing/cavitary; PVL toxin in CA-MRSA

Anaerobes: aspiration, poor dentition; foul sputum; lung abscess

PJP: HIV CD4 <200; bilateral interstitial; elevated LDH; treat TMP-SMX + steroids if PaO₂ <70

Coxiella burnetii (Q fever): livestock, parturient animals

Chlamydophila psittaci: parrots and exotic birds

Francisella tularensis: rabbits, ticks

Histoplasma: Ohio/Mississippi valleys; bird/bat droppings; mediastinal LAD

Coccidioides: Southwest US; erythema nodosum; eosinophilia

Blastomyces: Great Lakes, Mississippi/Ohio; skin and bone involvement

Cryptococcus: AIDS, transplant; pigeon droppings; meningitis

CURB-65 cutoffs: 0–1 outpatient, 2 ward, ≥3 inpatient ± ICU

PSI Class I–II outpatient; IV–V inpatient

Stop date prediction: minimum 5 days; longer for resistant or complicated cases

Antibiotic timing: ≤1 h in sepsis, ≤4 h in stable inpatient

MRSA nares NPV ~99% → negative result lets you stop empiric vancomycin

Procalcitonin: for de-escalation, not initial decision

Key distinction: Atypicals don't have cell walls (Mycoplasma) or are intracellular (Chlamydophila, Legionella) → β-lactams fail; need macrolide, doxycycline, or fluoroquinolone.

Board pearl: Currant-jelly sputum + alcohol use + upper-lobe cavitary infiltrate = Klebsiella.

Board Question Stem Patterns

— A vignette listing exact age, BUN, RR, BP, mentation—calculate and pick disposition

— Always check room-air SpO₂—hypoxia overrides a low score

— Recent cruise, hotel, or hot-tub exposure + hyponatremia + diarrhea + confusion + transaminitis → send urinary Legionella antigen, treat with macrolide or fluoroquinolone

— Patient improving after flu, then sudden worsening with cavitary infiltrate and hemoptysis → MRSA (or S. aureus); add vancomycin or linezolid

— Witnessed aspiration with infiltrate at 4 hours, resolving by 48 h → pneumonitis, no antibiotics

— Infiltrate at day 4 with fever and foul sputum → pneumonia, amoxicillin-clavulanate

— 60-year-old smoker, persistent RML infiltrate at 6 weeks → CT chest + bronchoscopy to rule out obstructing tumor; not "broader antibiotics"

— 68-year-old discharged after pneumonia, never received pneumococcal vaccine → administer PCV20 (or PCV15 + PPSV23) before discharge

— Persistent fever and pleural effusion with pH 7.1, glucose 30, positive Gram stain → chest tube drainage, antibiotics alone insufficient

— CD4 <200, bilateral interstitial, hypoxemia disproportionate to imaging, LDH elevated → TMP-SMX + steroids if PaO₂ <70 or A-a >35

— ICU patient with vasopressor-requiring sepsis from CAP → add hydrocortisone 200 mg/day ×7 days

— Healthy 35-year-old with no comorbidities, CURB-65 0 → amoxicillin 1 g TID (not azithromycin alone, not levofloxacin)

— Diabetic, hypertensive 55-year-old, CURB-65 1 → amoxicillin-clavulanate + macrolide OR respiratory fluoroquinolone

— Patient meets Halm criteria, family wants "another night" → discharge today with follow-up in 1 week

— Cultures pending at discharge—who follows up? → assign explicitly to PCP, document handoff

The "calculate CURB-65" stem:

The "Legionella unmasked" stem:

The "post-influenza superinfection" stem:

The "aspiration pneumonitis vs pneumonia" stem:

The "non-resolving pneumonia" stem:

The "missed vaccine" stem:

The "empyema" stem:

The "PJP in HIV" stem:

The "severe CAP with shock" stem:

The "outpatient prescription" stem:

The "comorbid outpatient" stem:

The "discharge readiness" stem:

The "transitions of care" stem:

Step 3 management: Read the last sentence first—it tells you whether the question is about diagnosis, antibiotics, disposition, or discharge planning.

Board pearl: When the vignette pairs pneumonia + hyponatremia, the answer almost always involves Legionella.

One-Line Recap

In community-acquired pneumonia, confirm with chest imaging, stratify severity with CURB-65 or PSI plus clinical judgment (always check room-air SpO₂), select empiric antibiotics by site of care and MRSA/Pseudomonas risk, escalate to ICU using IDSA/ATS major/minor criteria, and discharge with vaccines, smoking cessation, and a 7-day follow-up plan.

— Healthy outpatient → amoxicillin (or doxycycline)

— Comorbid outpatient → amoxicillin-clavulanate + macrolide OR respiratory fluoroquinolone

— Ward inpatient → β-lactam + macrolide OR respiratory fluoroquinolone

— ICU → β-lactam + macrolide (add MRSA/Pseudomonas coverage if risk factors); add hydrocortisone in severe CAP with shock

Triage rule: CURB-65 0–1 → outpatient; 2 → ward; ≥3 → inpatient/ICU—but hypoxemia, inability to take POs, or unsafe home situation overrides a low score and mandates admission

Empiric antibiotics by setting:

Don't miss the killers: Legionella (hyponatremia, diarrhea, confusion → urinary antigen, macrolide/fluoroquinolone); post-influenza MRSA (cavitary, hemoptysis → vancomycin/linezolid); PJP in HIV (bilateral interstitial, high LDH → TMP-SMX + steroids); empyema (pH <7.20 → chest tube)

Discharge checklist (every CAP, every time): pneumococcal + influenza vaccines updated, smoking cessation counseling, antibiotic duration ≥5 days and clinically stable per Halm, PCP follow-up scheduled within 7 days, return precautions reviewed, follow-up CXR at 6–8 weeks for smokers >50 or persistent symptoms

Board pearl: The Step 3 CAP question almost always has a management or transition-of-care twist—the right answer is rarely "order one more test"; it is usually "give the vaccine, schedule the follow-up, or de-escalate antibiotics based on the MRSA nares result."