What are the different types of pneumonia and their treatment options?

Pneumonia Types and Treatment

Classification of Pneumonia

Pneumonia is classified into distinct categories based on the setting of acquisition, each with different causative pathogens and treatment approaches.

Community-Acquired Pneumonia (CAP)

CAP is defined as pulmonary parenchymal infection acquired in the community, not in a healthcare setting. 1

• Most common bacterial pathogen: Streptococcus pneumoniae accounts for 50-90% of pyogenic pneumonia cases in middle-aged and older adults 1
• Age-specific pathogens: Viral agents (respiratory syncytial virus, parainfluenza) predominate in children <5 years; Mycoplasma pneumoniae is a major cause in patients 5-25 years of age 1
• Atypical pathogens: Include Mycoplasma pneumoniae, Legionella pneumophila (5-20% of hospitalized cases), Chlamydophila pneumoniae, and Coxiella burnetii 1
• Other bacterial causes: Haemophilus influenzae, Staphylococcus aureus, mixed aerobic-anaerobic bacteria, and gram-negative bacilli like Klebsiella pneumoniae are less common 1

Hospital-Acquired Pneumonia (HAP)

HAP is defined as pulmonary parenchymal infection occurring ≥48 hours after hospital admission or within 14 days after discharge. 1

• Common pathogens: Aerobic gram-negative bacilli (Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumoniae, Acinetobacter species) and gram-positive cocci (Staphylococcus aureus, particularly MRSA) 1
• Timing matters: Early-onset HAP (first 4 days) typically involves antibiotic-sensitive bacteria with better prognosis; late-onset HAP (≥5 days) more likely involves multidrug-resistant (MDR) pathogens 1
• Mortality: Crude mortality ranges from 30-70%, with attributable mortality estimated at 33-50% 1

Ventilator-Associated Pneumonia (VAP)

VAP is defined as pulmonary parenchymal infection occurring ≥48 hours after endotracheal intubation. 1

• Risk timeline: Highest risk occurs early (3%/day during first 5 days of ventilation), with approximately half of VAP episodes occurring within the first 4 days 1
• Pathogens: Similar to HAP, with P. aeruginosa (16.9%), S. aureus (12.9%), Klebsiella species (11.6%), and Enterobacter species (9.4%) being most common 1
• Polymicrobial infections: Rates vary widely but are especially high in patients with ARDS 1

Healthcare-Associated Pneumonia (HCAP)

HCAP is defined as pneumonia in patients with recent healthcare exposure, including hospitalization for ≥2 days within 90 days, nursing home residence, recent IV antibiotic therapy, chemotherapy, chronic wound care, or hemodialysis within 30 days. 1

• Important caveat: The 2016 IDSA/ATS guidelines removed HCAP as a distinct category in the US, but it remains relevant in certain healthcare systems (e.g., Taiwan) with unique epidemiology 1
• Risk stratification: HCAP should be stratified by risk for MDR organisms, with low-risk cases treated as CAP and high-risk cases treated as HAP/VAP 1
• Subcategories: Include nursing home-acquired pneumonia (NHAP), pneumonia in respiratory care wards, and hemodialysis-associated pneumonia (HDAP) 1

Aspiration Pneumonia

Aspiration pneumonia results from inhalation of oropharyngeal secretions, typically in patients with impaired consciousness, dysphagia, or compromised airway protection. 1, 2

• Community setting: Involves normal oropharyngeal aerobic and anaerobic flora 1
• Healthcare setting: Additional risk for aerobic gram-negative bacilli and S. aureus 1
• Modern understanding: Current guidelines recommend against routinely adding specific anaerobic coverage unless lung abscess or empyema is suspected 2

Risk Factors for Multidrug-Resistant Pathogens

Patients with any of the following risk factors should be treated with broader-spectrum antibiotics covering MDR organisms: 1

• Antimicrobial therapy in preceding 90 days 1
• Current hospitalization ≥5 days 1
• High frequency of antibiotic resistance in the community or specific hospital unit 1
• Hospitalization for ≥2 days in preceding 90 days 1
• Residence in nursing home or extended care facility 1
• Home infusion therapy (including antibiotics) 1
• Chronic dialysis within 30 days 1
• Home wound care 1
• Family member with MDR pathogen 1
• Immunosuppressive disease and/or therapy 1

Treatment Approaches by Pneumonia Type

Community-Acquired Pneumonia Treatment

For outpatients without comorbidities: Amoxicillin is the first-choice oral antibiotic at high doses (90 mg/kg/day in children, up to 4000 mg/day in adults) 1

For hospitalized patients with non-severe CAP: β-lactam (ceftriaxone 1-2g daily or cefotaxime 1-2g every 8 hours) plus macrolide (azithromycin 500mg daily or clarithromycin 500mg twice daily), OR respiratory fluoroquinolone (levofloxacin 750mg daily or moxifloxacin 400mg daily) 1

For severe CAP requiring ICU admission: β-lactam plus macrolide OR β-lactam plus fluoroquinolone 1

Duration: Minimum 3 days for hospitalized patients, with treatment continuing until clinical stability is achieved 3

Special considerations:

• Test all patients for COVID-19 and influenza when these viruses are circulating in the community 1, 3
• Add MRSA coverage (vancomycin 15mg/kg every 12 hours or linezolid 600mg every 12 hours) if risk factors present: recent hospitalization, prior respiratory isolation of MRSA, or nasal PCR positive 1
• Add P. aeruginosa coverage (piperacillin-tazobactam 4.5g every 6 hours, cefepime 2g every 8 hours, or meropenem 1g every 8 hours) if structural lung disease or prior isolation 1
• Systemic corticosteroids within 24 hours may reduce 28-day mortality in severe CAP 3

Hospital-Acquired and Ventilator-Associated Pneumonia Treatment

For early-onset HAP/VAP without MDR risk factors: Treat with antibiotics covering antibiotic-sensitive bacteria 1

For late-onset HAP/VAP or patients with MDR risk factors: Empiric broad-spectrum coverage is essential 1

Empiric regimen for suspected P. aeruginosa: Antipseudomonal β-lactam (piperacillin-tazobactam 4.5g IV every 6 hours, cefepime 2g every 8 hours, ceftazidime 2g every 8 hours, meropenem 1g every 8 hours, or imipenem 500mg every 6 hours) 1, 4

For suspected MRSA: Vancomycin (15mg/kg every 8-12 hours, target trough 15-20 mg/mL) or linezolid (600mg every 12 hours) 1

For nosocomial pneumonia with P. aeruginosa: Combination therapy with antipseudomonal β-lactam plus aminoglycoside is recommended 5, 4

Critical pitfall: Delayed or inadequate antimicrobial therapy is associated with increased mortality, especially with bacteremia due to P. aeruginosa or Acinetobacter species 1

Healthcare-Associated Pneumonia Treatment

Risk stratification is essential: 1

• Low risk for MDROs: Treat as CAP with standard regimens 1
• High risk for MDROs: Treat as HAP/VAP with broad-spectrum coverage 1

For hemodialysis-associated pneumonia: Consider broader coverage for severe cases, as these patients have unique risk profiles 1

For nursing home patients: Consider risk of aspiration and atypical pathogens including Legionella species and influenza virus 1

Aspiration Pneumonia Treatment

For outpatients or hospitalized patients from home: β-lactam/β-lactamase inhibitor (amoxicillin-clavulanate 875mg/125mg twice daily orally, or ampicillin-sulbactam 3g IV every 6 hours), clindamycin, or moxifloxacin 400mg daily 2

For ICU patients or nursing home residents: Clindamycin plus cephalosporin, OR cephalosporin plus metronidazole 2

For severe cases with MRSA risk: Add vancomycin or linezolid 2

For patients with penicillin allergy: Aztreonam 2g IV every 8 hours plus vancomycin or linezolid (aztreonam has negligible cross-reactivity with penicillins) 2

Duration: Should not exceed 8 days in patients who respond adequately 2

Critical guideline change: Modern evidence shows that routine anaerobic coverage is NOT recommended unless lung abscess or empyema is present, as aerobes and mixed cultures are more common than pure anaerobic infections 2

Special Populations

Pediatric Pneumonia

Hospitalization criteria: 1

• All infants <6 months of age 1
• Oxygen saturation <92% on room air 1
• Signs of respiratory distress (tachypnea: >60 breaths/min in 0-2 months, >50 in 2-12 months, >40 in 1-5 years, >20 in >5 years; retractions; grunting; nasal flaring) 1
• Significant comorbidities (immunologic disorders, cardiac or chronic pulmonary conditions) 1
• Dehydration, vomiting, or inability to take oral medication 1

Outpatient treatment: High-dose amoxicillin (90 mg/kg/day divided into 2-3 doses, maximum 4000 mg/day) is first-line for non-severe bacterial CAP 1

Alternative antibiotics: Amoxicillin-clavulanate, second-generation cephalosporins, or for penicillin allergy: levofloxacin, moxifloxacin, or linezolid 1

Immunocompromised Patients

Broader pathogen spectrum: Include Pneumocystis jirovecii, mycobacteria, Nocardia species, fungi, and cytomegalovirus in addition to typical bacterial pathogens 1

Diagnostic approach: Aggressive evaluation often required, as local signs may be diminished in neutropenic patients 1

Common Pitfalls to Avoid

• Do not assume all aspiration pneumonia requires anaerobic coverage - this increases Clostridioides difficile risk without mortality benefit 2
• Do not add MRSA or pseudomonal coverage without risk factors - this contributes to antimicrobial resistance without improving outcomes 2
• Do not delay appropriate antibiotics in HAP/VAP - this is associated with significantly increased mortality 1
• Do not ignore local antibiogram data - pathogen resistance patterns vary significantly by hospital and geographic region 1
• Do not overlook viral etiologies - up to 40% of hospitalized CAP patients with identified pathogens have viral causes 3