Section 1 — Epidemiology
Burden of Disease
CAP is a leading cause of infectious disease mortality worldwide, with incidence rising sharply with age and comorbidities.
248
per 100,000
Annual Incidence (all adults)
634
per 100,000
Adults 65–79 years
16,430
per 100,000
Adults ≥80 years
6%
30-day mortality
Hospitalized patients
34%
30-day mortality
Treatment failure
9×
higher rate
COPD patients
Section 2 — Microbiology
Causative Organisms
In 62% of hospitalized CAP cases, no pathogen is identified. Bacterial-viral co-infection is common.
| Pathogen |
Category |
Notes |
| Streptococcus pneumoniae |
Most Common |
Leading bacterial cause |
| Haemophilus influenzae |
Common |
40% of bacterial isolates |
| Mycoplasma pneumoniae |
Atypical |
Cyclical incidence pattern |
| Chlamydia pneumoniae |
Atypical |
Common cause |
| Legionella spp. |
Atypical |
3% of hospitalized CAP |
| Moraxella catarrhalis |
Less Common |
Often in COPD patients |
| Respiratory Viruses |
23% |
Rhinovirus, influenza most common |
⚠️
Elderly patients may NOT present with fever. Altered mental status may be the only presenting sign. Maintain high clinical suspicion.
Section 3 — Diagnosis
Clinical & Diagnostic Approach
CAP requires both clinical features AND radiographic confirmation. Lung ultrasound is now a guideline-approved alternative.
1
Clinical Suspicion
Cough + fever/chills + sputum ± dyspnea ± pleuritic chest pain. Assess vital signs, mental status, oxygen saturation.
2
Imaging Confirmation
CXR (Standard)
LUS (ATS 2025 — if trained)
CT (if equivocal)
CXR PPV 26.9% vs CT · NPV 96.5% · LUS more accurate than CXR per meta-analysis
3
Laboratory Testing
Routine: CBC (often elevated WBC), BMP as indicated
Severe CAP / MRSA risk: Sputum culture, MRSA nares, urine antigens
Flu season / viral symptoms: Test for influenza + COVID-19
Procalcitonin — NOT recommended (IDSA) · Urine antigen — NOT routine
Section 4 — Severity Assessment
CURB-65 Score
Simple 5-variable tool for risk stratification. Guides outpatient vs. inpatient decision. No labs required for CRB-65.
| Criterion |
Variable |
Points |
| Confusion |
New onset with this illness |
1 |
| Urea |
> 7 mmol/L (BUN > 19 mg/dL) |
1 |
| Respiratory rate |
≥ 30 breaths/min |
1 |
| Blood pressure |
SBP < 90 mmHg or DBP ≤ 60 mmHg |
1 |
| Age ≥ 65 |
Years |
1 |
Score 0–1
Low Risk
Mortality: 0.5–5%
🏠 Outpatient treatment
Score 2
Moderate Risk
Mortality: ~5.1%
🏥 Consider hospitalization
Score 3–4
High Risk
Mortality: 18.9%
🏨 Hospitalize · Consider ICU
Section 5 — Treatment
Empiric Antibiotic Therapy
Start empiric antibiotics promptly. Doxycycline is now the preferred first-line agent for most outpatients. Key ATS 2025 update: shorter durations (3–5 days) are now recommended.
Outpatient — Previously Healthy
No comorbidities · No antibiotics in past 3 months
| ⭐ Preferred |
Doxycycline
100 mg PO BID
|
| Alternative |
Amoxicillin
1 g PO TID
|
Outpatient — Comorbidities or Recent Antibiotics
Chronic heart/lung/liver/renal disease · DM · Alcoholism · Malignancy · Asplenia · Immunosuppression · Antibiotic use in past 3 months
| Regimen |
Dose |
Notes |
⭐ Preferred
Doxycycline + Amoxicillin |
100 mg BID +
1 g TID |
Combination therapy |
Alternative
Doxycycline + Cefpodoxime |
100 mg BID +
200 mg BID |
Alt combination |
Monotherapy
Levofloxacin |
750 mg PO daily |
Contact ASP if needed |
💡
ATS 2025 Update: For outpatients WITH comorbidities who test positive for a respiratory virus (influenza/COVID) and are clinically stable — consider NOT adding empiric antibiotics to reduce unnecessary antibiotic use.
Inpatient — Non-Severe CAP
Beta-lactam + Macrolide OR Beta-lactam + Doxycycline
Beta-lactams: Ceftriaxone, Cefotaxime, Ampicillin-sulbactam
Macrolide: Azithromycin 500 mg daily × 3 doses (atypicals); for Legionella → 7 days
Inpatient — Severe CAP
Combination therapy MANDATORY
Beta-lactam + Macrolide or Beta-lactam + Doxycycline
+ MRSA coverage (if prior MRSA isolation, recent hospitalization + parenteral ABx): Vancomycin or Linezolid
+ Pseudomonas coverage (if prior Pseudomonas isolation, recent hospitalization + parenteral ABx): Pip-tazo, Cefepime, Ceftaz, Imipenem, Meropenem, or Aztreonam
⚠️
Obtain cultures BEFORE escalating coverage — allows de-escalation if MRSA/Pseudomonas not confirmed
Section 6 — Duration of Therapy
ATS 2025: Shorter Is Better
Key paradigm shift: 3–5 days is now the standard duration for non-severe CAP achieving clinical stability. CXR abnormalities persisting up to 6 weeks are NOT a reason to extend antibiotics.
Non-Severe CAP
3–5 Days
Outpatient + Inpatient non-severe, after clinical stability achieved
Complicated / Confirmed Pathogens
≥7 Days
MRSA, Pseudomonas, Legionella
Stop Antibiotics When ALL Met:
✅ Afebrile 48–72 hours
✅ HR ≤ 100/min
✅ RR ≤ 24/min
✅ SBP ≥ 90 mmHg
✅ O₂ sat ≥ 90%
✅ Alert & oriented
⏱️
Cough and CXR abnormalities may take up to 6 weeks to resolve — this is NOT a valid reason to extend antibiotic courses.
Section 7 — Corticosteroids in CAP
Evidence, Trials & Selection Criteria
Evidence has evolved significantly — landmark trials now support specific steroid use in severe CAP with demonstrated mortality benefit for certain agents.
Landmark Trials
| Trial |
Year |
Agent |
Key Finding |
| CAPE COD ⭐ |
2022 |
Hydrocortisone 200 mg/d IV |
Mortality: 6.2% vs 11.9% (p=0.006); absolute ↓5.6%. Most robust evidence |
| ESCAPe |
2016 |
Methylprednisolone 0.5 mg/kg/d |
No mortality benefit; ↓ need for mechanical ventilation |
| Santeon-CAP |
2022 |
Dexamethasone 6 mg/d |
No mortality benefit; ↓ ICU admissions in severe subgroup |
| SONIA |
2024 |
Low-dose glucocorticoids |
16% ↓ in 30-day mortality (low-resource setting) |
| Lancet Respir Med (8 RCTs) |
2024 |
Various |
28% ↓ in 30-day mortality (OR 0.72) |
| BMJ Open Resp Research |
2024 |
Various (severe CAP) |
30% ↓ in all-cause mortality (RR 0.70) |
Which Steroid? Evidence by Agent
Hydrocortisone ⭐
Mortality Benefit YES
Most consistent evidence — CAPE COD RCT + meta-analyses confirm mortality reduction
Methylprednisolone
No mortality benefit
ESCAPe negative for mortality; may reduce need for MV
Dexamethasone
Mortality benefit not shown
Santeon-CAP negative; NMA inconclusive for mortality
Selection Criteria — Who Should Receive Steroids?
✅ Indications — Severe CAP (ATS 2025 — conditional; SCCM 2024 — strong)
• Invasive mechanical ventilation
• Septic shock requiring vasopressors
• HFNC with FiO₂ ≥50% + PaO₂/FiO₂ <300
• PSI Class V (>130)
• ≥3 minor criteria (RR≥30, PaO₂/FiO₂<250, multilobar, confusion, BUN≥20, WBC<4K, PLT<100K, Temp<36°C)
✅ Best Response: High Inflammatory State
CRP ≥ 200 mg/L
Strong predictor of mortality benefit from steroids
Also important:
Administer within 24 hours of meeting severe CAP criteria
Contraindications & Cautions
| Situation |
Recommendation |
| Non-severe CAP |
Against ATS 2025 — strongly recommends NOT using |
| Influenza pneumonia |
Avoid — ↑ mortality, impaired viral clearance |
| Fungal pneumonia |
Avoid — no benefit in observational data |
| High-dose short-duration (>400 mg hydrocortisone equiv. <3 days) |
Not recommended for septic shock |
| Uncontrolled hyperglycemia |
⚠️ Monitor closely — steroids worsen glucose |
| GI bleeding risk |
⚠️ Stress ulcer prophylaxis recommended |
Dosing Regimen
Agent
IV Hydrocortisone ⭐
preferred (CAPE COD evidence)
Dose
200 mg/day
50 mg IV q6h OR continuous infusion
Duration
5–7 days
Consider taper if >7 days
Alternative: Methylprednisolone 40–80 mg/day IV if hydrocortisone unavailable
⚠️
SCCM 2024 Focused Update: Strongly recommends corticosteroids for adults hospitalized with severe bacterial CAP. ATS 2025: Suggests for severe CAP (conditional); strongly recommends against for non-severe CAP.
Section 8 — Prevention
Pneumococcal Vaccination
Updated 2022 ACIP guidelines recommend PCV20 or PCV15+PPSV23 sequence for adults ≥65 and high-risk younger adults.
| Population |
Vaccine Regimen |
| Adults ≥65 years |
PCV20 alone OR
PCV15 + PPSV23 (≥1 year later)
|
| Ages 19–64 with comorbidities |
PCV20 alone OR
PCV15 + PPSV23 (≥1 year later)
|
| Previously received PCV13 only |
No additional PCV20/PCV15 needed |
| Previously received PPSV23 only |
Give PCV15 or PCV20 ≥1 year after PPSV23 |
Vaccine efficacy: PPSV23 reduces relative risk of CAP by 13% overall; 28% in adults ≥65 or high-risk younger adults. Annual influenza and COVID-19 vaccination recommended for all adults.
Section 9 — Key Updates
ATS 2025 vs. IDSA/ATS 2019
Major changes in the 2025 ATS update that differ from the 2019 joint IDSA/ATS guidelines.
Lung Ultrasound
Not specified
Steroids (non-severe)
Not recommended
Steroids (severe)
Not recommended
Viral + outpatient w/ comorbidities
Always add antibiotics
Doxycycline (outpatient)
Alternative agent
Duration
3–5 days if stable
Lung Ultrasound
Acceptable alternative to CXR/CT
Steroids (non-severe)
Explicitly against
Steroids (severe)
Conditionally suggested
Viral + outpatient w/ comorbidities
Consider NO antibiotics if stable
Doxycycline (outpatient)
Preferred first-line
Section 10 — ICU Management
Severe CAP: ICU Criteria & Management
10–30% of hospitalized CAP patients require ICU. Severe CAP = ≥1 major criterion OR ≥3 minor criteria (IDSA/ATS 2019, endorsed ATS 2025).
ICU Admission Criteria
Major Criteria (≥1 = ICU)
Septic Shock
Hypotension requiring vasopressors
Respiratory Failure
Requiring invasive mechanical ventilation
Minor Criteria (≥3 = ICU)
Hypotension requiring fluids
Antibiotic Therapy — Severe CAP
Mandatory Combination Therapy
Beta-lactam
Ceftriaxone, Cefotaxime, or Ampicillin-sulbactam
+ Macrolide OR Doxycycline
Azithromycin 500mg daily × 3d
OR Doxycycline 100mg BID
If MRSA Risk (prior isolation / recent hospitalization + IV antibiotics):
Add Vancomycin or Linezolid
If Pseudomonas Risk:
Add Pip-tazo, Cefepime, Ceftaz, Imipenem, Meropenem, or Aztreonam
⚠️
Obtain blood + sputum cultures BEFORE starting antibiotics — enables targeted de-escalation when results return
Respiratory & Hemodynamic Support
Severe Hypoxia / Respiratory Failure
PaO₂ < 55 mmHg despite O₂, or hypercapnia with pH < 7.35 → Intubate
Before intubation: HFNC or NPPV may reduce need for intubation
ARDS → Lung-protective ventilation:
Tidal volume 6 mL/kg IBW
Plateau pressure < 30 cm H₂O
Prone positioning if PaO₂/FiO₂ < 150
Septic Shock — Hemodynamic Support
1. Fluids: 30 mL/kg crystalloid bolus, then reassess
2. Vasopressors: Norepinephrine first-line; target MAP ≥ 65 mmHg
3. Steroids (ATS 2025 — conditional):
Consider if high inflammatory markers, ICU admission, or complicated respiratory failure. Give within 24h of meeting severe CAP criteria.
Mortality & Complications
21–55%
ICU mortality
Severe CAP
56%
in-hospital
Severe CAP mortality
40.7%
1-year
post-discharge mortality
~30%
of severe CAP
develop ARDS
Complications
ARDS, Empyema, Lung abscess, Septic shock, Multisystem organ failure, Cardiac complications (MI, arrhythmia)
Key Pathogens
S. pneumoniae (incl. DRSP), S. aureus (MRSA), Legionella, Pseudomonas, GNEB, Polymicrobial → worse prognosis
Key Risk Factors
Age ≥65, COPD, chronic disease, DM, alcoholism, obesity, delayed antibiotics (every hour ↑ mortality)
Severe vs. Non-Severe CAP — Key Differences
Antibiotics
Doxycycline ± Amoxicillin
MRSA/ Pseudomonas
Not routine
Steroids
Against (ATS 2025)
Duration
3–5 days if stable
Antibiotics
Beta-lactam + Macrolide/Doxycycline
MRSA/ Pseudomonas
Add if risk factors
Steroids
Suggested if criteria met (ATS 2025)
Cultures
Blood + sputum mandatory
Duration
5–7 days minimum; longer if complicated
Summary — Key Takeaways
Clinical Pearls
-
1
Diagnose with clinical features + imaging. CXR is standard; lung ultrasound is now guideline-approved (ATS 2025) when operators are trained.
-
2
Use CURB-65 to guide setting. Score 0–1 = outpatient; 2 = consider admission; 3–4 = hospitalize/ICU.
-
3
Doxycycline is now preferred first-line for most outpatients. Combination therapy (doxycycline + amoxicillin) for those with comorbidities or recent antibiotic use.
-
4
Shorten duration to 3–5 days if clinical stability achieved. Do NOT extend just because CXR or cough hasn't cleared.
-
5
De-escalate promptly. Get cultures before broadening coverage. Stop MRSA/Pseudomonas coverage if not confirmed.
-
6
No corticosteroids for non-severe CAP. Consider only for severe CAP (ATS 2025 conditional) or refractory septic shock.
-
7
Vaccinate appropriately. PCV20 alone or PCV15 + PPSV23 for adults ≥65 and high-risk 19–64 year-olds.
-
8
Severe CAP = ICU when ≥1 major criterion or ≥3 minor criteria (IDSA/ATS). 10–30% of hospitalized CAP need ICU.
-
9
Severe CAP: Beta-lactam + Macrolide is mandatory first-line; add MRSA/Pseudomonas coverage only with risk factors.
-
10
Time is life. Every hour delay in antibiotics increases mortality in severe CAP. ICU mortality: 21–55%.
References
1. Metlay JP, et al. Diagnosis and treatment of adults with community-acquired pneumonia. Am J Respir Crit Care Med. 2019;200(7):e45-e67. doi:10.1164/rccm.201908-1581ST
2. American Thoracic Society. Clinical Practice Guideline Updates for the Diagnosis and Management of CAP (2025). Am J Respir Crit Care Med. 2025.
3. UCSF IDMP. VASF Community-Acquired Pneumonia Treatment Guidelines. November 2023.
4. Ebell MH. Community-Acquired Pneumonia in Adults: Rapid Evidence Review. Am Fam Physician. 2022;105(6):625-630.
5. CDC. Pneumococcal Vaccination Recommendations. 2022.