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Pneumonia, Bacterial

BASICS

  • Definition: Acute infection of the pulmonary parenchyma caused by bacteria.
  • Classification:
  • Community-Acquired Pneumonia (CAP): Outpatient, Nonsevere Inpatient, Severe/ICU.
  • Nosocomial Pneumonia:
    • Hospital-Acquired Pneumonia (HAP): ≥48 hours after admission.
    • Ventilator-Associated Pneumonia (VAP): ≥48 hours after intubation.

EPIDEMIOLOGY

  • CAP Incidence: 24.8 cases/10,000 adults/year in US; 5–6/1,000 persons/year.
  • Leading infectious cause of death (esp. in children <5 years globally).
  • HAP: 5–20/1,000 admissions; VAP incidence 6–20x higher in ventilated patients.

ETIOLOGY AND PATHOPHYSIOLOGY

  • Outpatient CAP (Adults):
  • Typical (85%): Streptococcus pneumoniae, Haemophilus influenzae, Staph aureus, group A Strep, Moraxella catarrhalis.
  • Atypical (15%): Legionella, Mycoplasma pneumoniae, Chlamydophila pneumoniae.
  • Inpatient, Severe CAP/HAP/VAP:
  • Gram-negatives: Pseudomonas, E. coli, Klebsiella, Acinetobacter.
  • Gram-positives: Streptococcus spp., Staph aureus (incl. MRSA).
  • Pediatric:
  • Birth–3 weeks: E. coli, GBS, Listeria.
  • <3 months: C. trachomatis, S. pneumoniae, H. influenzae.
  • 3 mo–18 yrs: S. pneumoniae, C. pneumoniae, M. pneumoniae.

RISK FACTORS

  • Immunosuppression (steroids, HIV, transplant, TNF-α inhibitors)
  • Chronic illnesses (asthma, COPD, diabetes, CKD, CHF, liver disease)
  • Age >65, recent antibiotics/hospitalization
  • Functional decline, poor oral hygiene, tobacco use

GENERAL PREVENTION

  • Vaccination:
  • Children: PCV13 at 2, 4, 6, 12–15 months
  • Adults ≥65 years: PCV20 (per CDC recommendations)
  • At-risk adults 19–64: PCV20 if chronic disease
  • Annual influenza vaccination
  • Smoking cessation

DIAGNOSIS

History

  • Fever, chills, rigors, malaise, fatigue, dyspnea, cough (± sputum), pleuritic chest pain, myalgias, GI symptoms.
  • Pediatrics: lethargy, hypotonia, poor feeding, vomiting.

Physical Exam

  • Fever, tachypnea, tachycardia, hypoxemia
  • Decreased breath sounds, rales, rhonchi, egophony, increased fremitus, dull percussion
  • Grunting, retractions in children

Special Populations

  • Older adults: may present with confusion, weakness, falls
  • Infants <3–6 months: higher risk, admit for inpatient treatment

DIFFERENTIAL DIAGNOSIS

  • Viral pneumonia, bronchitis, asthma/COPD exacerbation, pulmonary edema, tuberculosis, lung cancer, pneumonitis, rheumatologic causes

DIAGNOSTIC TESTS & INTERPRETATION

Outpatient

  • Clinical diagnosis; no routine labs/imaging for healthy adults.

Inpatient

  • CBC, CRP, chest x-ray.
  • Severe cases: blood/sputum cultures, urine pneumococcal/Legionella antigens, endotracheal aspirate (if intubated).
  • Procalcitonin is NOT recommended.
  • MRSA/Pseudomonas risk: screen with rapid tests; cover if positive.

Pediatrics

  • Viral testing in children <2 years (high viral etiology)
  • CXR, cultures for severe or complicated cases

TREATMENT

Severity Scoring

  • Use PSI or CURB-65 for admission/level of care decisions, but clinical judgment is essential.

Adults

  • CAP, Outpatient (No MRSA/Pseudomonas/comorbidity):
  • Doxycycline 100 mg BID
  • OR Azithromycin (if local resistance <25%)
  • CAP, Outpatient (Comorbidity):
  • Doxycycline 100 mg BID PLUS
  • Amox/clav 875/125 mg BID OR cefpodoxime 200 mg BID OR cefuroxime 500 mg BID
  • OR monotherapy with respiratory fluoroquinolone
  • CAP, Inpatient Nonsevere:
  • β-lactam (ceftriaxone/amp-sulb/cefotaxime) + macrolide (azithro/clarithro)
  • OR respiratory fluoroquinolone monotherapy
  • CAP, Inpatient Severe:
  • β-lactam + macrolide OR β-lactam + respiratory fluoroquinolone
  • If MRSA risk: add vancomycin or linezolid
  • If Pseudomonas risk: add cefepime/meropenem/pip-tazo/aztreonam
  • Duration: Minimum 5 days; IV→PO switch when stable.

HAP/VAP

  • Cover S. aureus, Pseudomonas, other Gram-negatives
  • Add MRSA coverage if at risk or local prevalence high
  • Double Pseudomonas coverage if high resistance risk or unknown susceptibilities

Pediatrics

  • Outpatient, presumed typical: Amoxicillin 90 mg/kg/day PO BID (max 4g/day)
  • Outpatient, presumed atypical: Azithromycin or doxycycline (>7 yrs)
  • Inpatient, uncomplicated: Ampicillin or ceftriaxone; add vancomycin/clindamycin if CA-MRSA suspected
  • Duration: 5 days (outpatient), 7 days (<6 months), longer if complicated

ONGOING CARE

  • Supportive: Analgesia, antipyretics, O2, fluids as needed
  • Chest physiotherapy, minimize aspiration, monitor vitals
  • Patient education: Smoking cessation, vaccination

DISCHARGE CRITERIA (Inpatient)

  • Afebrile, stable HR/RR/O2, able to tolerate PO, mental status baseline, clinical improvement for 12–24 hrs

COMPLICATIONS

  • Necrotizing pneumonia, empyema, abscess, cavitation, bronchopleural fistula, sepsis, respiratory failure

ICD-10

  • J15.9 Unspecified bacterial pneumonia
  • J15.4 Pneumonia due to other streptococci
  • J14 Pneumonia due to Hemophilus influenzae

CLINICAL PEARLS

  • Always use a severity of illness score to guide disposition but confirm with clinical judgment.
  • Vaccination (pneumococcal, influenza) and smoking cessation are key prevention strategies.
  • Most pediatric pneumonia is viral—avoid unnecessary antibiotics.
  • Procalcitonin is NOT recommended for pneumonia management.
  • For MRSA or Pseudomonas risk: obtain rapid diagnostics, adjust antibiotics accordingly.
  • Short-course therapy (5 days) is effective for most uncomplicated cases.