For Medical Students

TL;DR

What you need to know before seeing your first patient on your IM rotation with this condition

Estimated read time: 4 minutes

• What it is: A new infiltrate on chest imaging, plus at least one respiratory symptom (cough, sputum, dyspnea, pleuritic pain), plus at least one other finding — abnormal lung sounds, fever ≥38°C, leukocytosis, or SpO2 <90%.
• How it presents: Cough, purulent sputum, dyspnea, pleuritic chest pain and fever.
• What the exam is worth: the JAMA Rational Clinical Examination is blunt — no single finding rules pneumonia in.
  • Egophony — LR+ 8.6
  • Temperature >37.8°C — LR+ 4.4
  • Bronchial breath sounds — LR+ 3.5
  • Crackles — LR+ 1.6–2.7
• Initial tests to order: Chest radiograph (PA and lateral). Room-air SpO2. CBC, electrolytes, creatinine and urea. Influenza and COVID-19 testing when circulating. Blood cultures, sputum culture and urine antigens are not routine — severity and risk factors decide those.
• If unstable: Septic shock needing vasopressors, or respiratory failure needing ventilation, each define severe pneumonia alone. Call your senior and involve critical care.
• If stable — the sequence: Score CURB-65 → decide home, ward or ICU → treat: outpatient amoxicillin 1 g PO TID; inpatient ceftriaxone 1–2 g IV daily plus azithromycin 500 mg daily → check the vaccine record before discharge.
• Duration: Five days is enough for uncomplicated CAP once stable 48 hours. Switch to oral as soon as they are afebrile and eating.

Listen

The Intern at WorkEpisode 48Community Acquired PneumoniaMicrobiology, presentation and empiric therapy for CAP — the anchor listen for this post. Mar 2020.Listen Now

For Residents

Read Around the Case

Based on the ATS/IDSA 2019 Community-Acquired Pneumonia Guideline and the IDSA CAP Clinical Pathway, with Canadian vaccine recommendations from NACI (November 2024)

Estimated read time: 14 minutes

Jump to: Severity · Testing · Antibiotics · Steroids · Duration · Aspiration & HAP · Vaccines

1. Severity and Disposition

Two separate questions. CURB-65 asks “hospital at all?” (CRB-65 drops the urea for primary care). The ATS/IDSA criteria ask “ICU?”

Severity & Disposition — the sequence

1. Confirm the diagnosis
New infiltrate on imaging, a respiratory symptom, and one other finding

2. Score CURB-65
Confusion · Urea >7 mmol/L · RR ≥30 · BP (SBP ≤90 or DBP ≤60) · age ≥65
0–1 → consider outpatient  |  2 → admit  |  ≥3 → admit and assess for ICU

3. Apply the ATS/IDSA severe criteria
1 major or ≥3 minor = severe pneumonia
Two minor criteria arrive in the bloodwork, not at the bedside

4. Treat — beta-lactam + atypical coverage
Stop at day 5 unless not yet stable 48h, or there is empyema, abscess or an unusual pathogen

Lobar pneumonia, right middle lobe — chest radiograph of a 67-year-old man. The opacity sits in the right mid-zone and obscures the right heart border, which localizes the consolidation to the adjacent middle lobe; a lower lobe consolidation would efface the hemidiaphragm instead. Image by Mikael Häggström, MD, CC0 via Wikimedia Commons. For more annotated films see the Radiology Masterclass chest gallery.

Severe CAP — the ATS/IDSA criteria

One major, or three or more minor, defines severe pneumonia and prompts the ICU conversation.

Criterion Type	Criteria
Major Any one = severe	Septic shock requiring vasopressors Respiratory failure requiring mechanical ventilation
Minor Three or more = severe	Respiratory rate ≥30 breaths/min PaO2/FiO2 ratio ≤250 Multilobar (≥2 lobes) infiltrates Confusion or disorientation Uremia (BUN ≥20 mg/dL, roughly urea ≥7.1 mmol/L) Leukopenia (WBC <4.0 × 109/L, from infection alone) Thrombocytopenia (platelets <100 × 109/L) Hypothermia (core temperature <36°C) Hypotension requiring aggressive fluid resuscitation

2. Diagnostic Testing by Severity

Testing is stratified by severity and resistance risk, not reflexive:

• Non-severe: blood cultures, sputum culture and pneumococcal urine antigen are not routine — yield is low and contaminants prompt unnecessary broadening. Respiratory culture only after recent hospitalization with IV antibiotics, when starting anti-MRSA or anti-pseudomonal cover, or in advanced structural lung disease.
• Severe: blood cultures, respiratory culture, and both urine antigens.
• Legionella antigen if non-severe: only with an outbreak, travel or other epidemiological reason.
• MRSA nasal swab: a useful negative — send after recent hospitalization with IV antibiotics, or when starting anti-MRSA cover.
• Viral testing: influenza and COVID-19 when circulating, plus expanded panels (RSV, human metapneumovirus, rhinovirus, parainfluenza, adenovirus) per the IDSA pathway. A positive virus with low suspicion of bacterial co-infection justifies deferring antibiotics.

3. Empiric Antibiotics

Coverage depends on setting. A healthy outpatient can have amoxicillin alone; most hospitalized patients need two drugs, aimed at two groups of organisms:

• Beta-lactam → typicals: Streptococcus pneumoniae above all (resistance is uncommon, which makes it the reliable anchor), plus Haemophilus influenzae, Moraxella catarrhalis and MSSA.
• Macrolide or doxycycline → atypicals: Mycoplasma pneumoniae, Legionella and Chlamydia pneumoniae.
• Why one drug cannot do both: beta-lactams block cell-wall cross-linking, and fail against atypicals for two reasons — Mycoplasma has no cell wall, while Legionella and Chlamydia are intracellular.
• A respiratory fluoroquinolone spans both halves in one drug, which is why it works as monotherapy.
• Always needed for inpatients? Debated — CAP-START found monotherapy non-inferior in non-ICU patients, but ATS/IDSA weighed it and still recommends two drugs.

Check your local antibiogram — regional resistance drives the choice more than any guideline.

Component	Options and Dosing	Comments
Outpatient
Healthy No comorbidities or resistance risk factors	Amoxicillin 1 g PO TID or doxycycline 100 mg PO BID or a macrolide (only where pneumococcal macrolide resistance <25%)	Atypical coverage is not required here — amoxicillin alone is a strong ATS/IDSA recommendation. The inpatient rule below is not universal.
With comorbidities Heart, lung, liver or renal disease, diabetes, alcoholism, malignancy, asplenia	Amoxicillin-clavulanate or a cephalosporin PLUS a macrolide or doxycycline or a respiratory fluoroquinolone alone	Comorbidity raises the stakes of missing an atypical.
Inpatient — non-severe
Beta-lactam Choose one	Ceftriaxone 1–2 g IV q24h (2 g if >80 kg; 2 g in severe CAP) Cefotaxime 1–2 g IV q8h	The Canadian first choice. The IDSA pathway also lists ampicillin-sulbactam, not marketed in Canada. Penicillin allergy: cross-reactivity with cephalosporins is well under 2% and driven by shared side chains, not the beta-lactam ring — so most patients labelled penicillin-allergic can receive ceftriaxone.
PLUS atypical coverage Choose one	Azithromycin 500 mg PO or IV q24h × 3 doses (1500 mg total) Clarithromycin 500 mg PO or IV q12h Doxycycline 100 mg PO or IV q12h	Note: doxycycline is not known to be QTc-prolonging — it appears on no CredibleMeds list, whereas azithromycin and clarithromycin are both Known Risk of Torsades. Useful if the patient is already on QT-prolonging drugs.
Monotherapy alternative If the above is not tolerated	Levofloxacin 750 mg PO or IV q24h Moxifloxacin 400 mg PO or IV q24h	Covers both groups in one drug. Canadian monographs carry a Serious Warnings and Precautions box: • Tendinopathy and tendon rupture (rare — about 3 extra per 10,000 treated) • Peripheral neuropathy • CNS and psychiatric effects • QT prolongation • Aortic aneurysm and dissection • Hyperglycaemia or hypoglycaemia • C. difficile Calcium, magnesium, iron and antacids bind it in the gut and reduce absorption — separate the doses.
Add based on history
MRSA coverage Prior MRSA, or recent hospitalization with IV antibiotics	Vancomycin per hospital dosing Linezolid 600 mg PO or IV q12h	A negative nasal swab has a high negative predictive value — supports stopping vancomycin.
Anti-pseudomonal cover Advanced structural lung disease, or prior Pseudomonas	Piperacillin-tazobactam 4.5 g IV q6h Cefepime 2 g IV q8h Ceftazidime 2 g IV q8h Meropenem 1 g IV q8h	By history, not by how the patient looks. De-escalate on cultures.

Trial Files

Antibiotic Stewardship for PneumoniaTrial Files — MedicinePodsBeta-Lactams Alone for CAPTrial Files — MedicinePods

The Intern at WorkInfographic + episodePenicillin AllergyHow to take the allergy history, and who labelled penicillin-allergic can safely receive a cephalosporin.Listen Now

4. Corticosteroids

The practical synthesis: consider hydrocortisone in severe CAP requiring ICU-level care. Do not give steroids in non-severe CAP — no demonstrated benefit, real harm from hyperglycemia and neuropsychiatric effects.

ATS/IDSA 2019 advises against routine corticosteroids — but predates CAPE COD (NEJM 2023): 800 ICU patients with severe CAP, hydrocortisone 200 mg/day by infusion, 28-day mortality 6.2% vs 11.9%. The earlier ESCAPe was neutral.

Check the boundaries. CAPE COD excluded septic shock on vasopressors and influenza; entry required mechanical ventilation, HFNC with FiO2 >0.5 and P/F <300, a non-rebreather with P/F <300, or PSI >130.

Separately: COPD or asthma may need steroids for the airway disease — a different indication.

Listen

The Rounds TableEpisode 65Hydrocortisone for PneumoniaRapid-fire appraisal of hydrocortisone in severe CAP — the CAPE COD trial. Pairs with section 4. Jul 2023.Listen Now

Dexamethasone for COVID PneumoniaTrial Files — MedicinePods

5. Duration, IV to Oral, and Follow-up Imaging

• Duration: five days for uncomplicated CAP, once stable 48 hours (afebrile, normalizing vitals, oxygenating, eating). The PTC trial stopped beta-lactams at day 3 in already-stable patients (day-15 cure 77% vs 68%). Longer only for empyema, abscess or an unusual pathogen.
• IV to oral: once stable, afebrile and eating, IV offers no advantage — it removes a line, a phlebitis risk and often a reason to stay. Ceftriaxone plus azithromycin steps down to oral amoxicillin; the macrolide usually stops, since azithromycin is three doses (1500 mg total).
• Follow-up imaging: repeat radiography before discharge is not indicated when someone is improving — clearing lags recovery by weeks, and an unchanged day-five film tempts the team into treating the image. Reserve it for persistent symptoms, or a smoker where malignancy must be excluded.

Biomarkers to Guide Antibiotic DurationTrial Files — MedicinePods

6. Aspiration and Hospital-Acquired Pneumonia

5–15% of all CAP, with higher mortality, and much of what gets taught is out of date. The 2023 CMAJ review corrects four things:

• No routine anaerobic coverage. Treat as CAP or HAP — anaerobes are not the primary pathogens. Clindamycin or metronidazole only for empyema, abscess or necrotizing disease. Most learners have this backwards.
• Aspiration pneumonitis is not pneumonia. Chemical injury from gastric contents, onset in minutes to hours, resolving in 24–48 hours. Supportive care — not antibiotics.
• Diagnosis is clinical and radiographic — no lab test confirms it. Key risk factors are dysphagia and altered consciousness; the right lower lobe is typical, gravity-dependent on CT.
• Feeding tubes do not reduce the risk. Nasogastric and gastrostomy feeding do not decrease aspiration or pneumonia rates versus oral intake. Prevention is swallowing assessment, upright positioning, texture modification and oral hygiene.

What to do: consult speech-language pathology for a bedside swallowing assessment before resuming oral intake, and ask for texture and positioning advice. Add oral care. And since feeding tubes do not reduce risk, a failed swallow assessment is not an automatic route to a tube.

Hospital-acquired pneumonia develops ≥48 hours after admission. Organisms shift toward S. aureus (including MRSA) and Gram-negatives including Pseudomonas, so coverage broadens then narrows on cultures.

Listen

The Intern at WorkEpisode 143Approach to Aspiration and HAPSeparates aspiration pneumonitis from aspiration pneumonia and hospital-acquired pneumonia. Pairs with section 6. May 2022.Listen NowThe Rounds TableBugs & DrugsAntibiotics in Aspiration PneumoniaDr. Paul Bunce on why routine anaerobic coverage is not needed in aspiration pneumonia.Listen Now

7. Vaccination and Prevention

An admission for pneumonia is the best chance to correct someone’s vaccine record, and it is routinely missed.

• Pneumococcal: NACI (Nov 2024) recommends one dose of Pneu-C-20 or Pneu-C-21 for adults 65+, and under 65 with risk factors for invasive pneumococcal disease. Product varies by province — check your local program.
• Influenza: annually. It is both a cause of pneumonia and a precursor to bacterial superinfection.
• COVID-19: per current NACI guidance for age and risk group.
• RSV: recommended for older adults — check local age and risk thresholds.
• Smoking cessation is a pneumonia intervention, not just a cardiovascular one.

Simultaneous Flu and RSV VaccinesTrial Files — MedicinePods

Related Podcasts

Other causes of pneumonia beyond the community-acquired picture.

The Intern at WorkEpisode 259The Internist’s Guide to PJPPneumocystis jirovecii pneumonia — who is at risk, how it presents, and why it is missed.Listen NowThe Intern at WorkUntangling the WebApproach to Cryptogenic Organizing PneumoniaThe pneumonia that does not respond to antibiotics — when to stop and think again. Apr 2026.Listen Now