- Clinical science
Pneumonia is a respiratory infection characterized by inflammation of the alveolar space and/or the interstitial tissue of the lungs. In industrialized nations, it is the leading infectious cause of death. Pneumonia is commonly transmitted via aspiration of airborne pathogens (primarily bacteria) but may also result from the aspiration of stomach contents. The spectrum of causal pathogens is mainly determined by patient age, immune status, and where the infection was acquired (community-acquired or hospital-acquired). Pneumonia is also classified based on clinical features as either typical and atypical; each type has its own spectrum of commonly associated pathogens. Typical pneumonia presents with sudden onset of malaise, fever, and a productive cough. On auscultation, crackles and bronchial breath sounds are audible. Atypical pneumonia, on the other hand, presents with gradual onset of unproductive cough, dyspnea, and extrapulmonary manifestations. Auscultation is typically unremarkable. In reality, some patients may present with elements of both types. Diagnostics include blood tests for inflammatory parameters and pathogen detection in blood, urine, or sputum samples. Chest x-ray in cases of typical pneumonia shows extensive opacity restricted to one lobe, while atypical pneumonia presents with diffuse, often subtle infiltrates. A newly developed pulmonary infiltrate on chest x-ray in combination with the clinical features confirms the diagnosis. Management consists of supportive measures, such as oxygen administration or physiotherapy, and antibiotic treatment. Antibiotics are initially administered empirically and later adapted based on the results of bacterial culture.
- Primary pneumonia: no apparent preexisting conditions that may predispose to pneumonia
- Secondary pneumonia
- Community-acquired pneumonia: (CAP: ): pneumonia that is acquired outside of a health care establishment
- Hospital-acquired pneumonia: (HAP: ): nosocomial pneumonia, with onset > 48 hours after admission
- Pneumonia with less distinct classical symptoms and often unremarkable findings on auscultation and percussion
- Manifests as interstitial pneumonia
|Type of pneumonia||Common pathogens|
|Pneumonia in immunocompromised patients|
|Pneumonia in newborn infants|
|Recurrent pneumonia|| |
Routes of infection
- Most common: microaspiration (droplet infection) of airborne pathogens or oropharyngeal secretions
- Aspiration of gastric acid ( ) , or of food or liquids
- Hematogenous dissemination in rare cases
- Old age and immobility of any cause
- Chronic diseases
- Immunosuppression (e.g., HIV infection, diabetes mellitus, cytostatic therapy, alcoholism, immunosuppressive therapy)
- Pulmonary protective mechanisms (cough reflex, mucociliary clearance , alveolar macrophages ) fail → microbial infiltration of the pulmonary parenchyma cannot be prevented
- Pathogen infiltrates pulmonary parenchyma → interstitial and alveolar inflammation → impaired alveolar ventilation → Ventilation/perfusion (V/Q) mismatch with intrapulmonary shunting (right to left) → hypoxia due to increased alveolar-arterial oxygen gradient (This effect is worsened if the affected lung is in the dependent position since perfusion is better to the dependent lung than the non-dependent lung)
Pattern of involvement
Lobar pneumonia: classic (typical) pneumonia of an entire lobe, primarily caused by pneumococci
- Classic disease progression in stages
- Congestion (day 1): serous exudate in blood-rich lungs, numerous bacteria evident
- Red hepatization (days 2–3): exudate rich in fibrin and inflammatory cells with many bacteria still visible; lungs take on a liver-like texture. Lung loses some spongy quality
- Gray hepatization (days 4–7): erythrocytes are degraded but inflammatory cells persist; most bacteria have been destroyed by this stage. Lung is now firm
- Resolution (day 8 to week 4): fibrinolysis by enzymatic means and removal of the purulent exudate via productive cough
- Classic disease progression in stages
- Bronchopneumonia: mostly descending infection that affects the bronchioles and adjacent alveoli; usually involves the lower lobes or right middle lobe; manifests as typical pneumonia
- Interstitial pneumonia: interstitial inflammation, particularly caused by mycoplasma and viral infections; manifests as atypical pneumonia
- Miliary pneumonia: multiple small infiltrations caused by hematogenous dissemination (e.g., of tuberculosis)
- Lobar pneumonia: classic (typical) pneumonia of an entire lobe, primarily caused by pneumococci
Typical pneumonia presents with a sudden onset of symptoms caused by lobar infiltration.
- Severe malaise
- High fever and chills
- Productive cough with purulent sputum (yellow-greenish)
- Tachypnea and dyspnea (nasal flaring, thoracic retractions)
- Pleuritic chest pain when breathing, often accompanying pleural effusion
- Pain projecting to the abdomen and epigastric region (particularly in children)
Atypical pneumonia typically takes an indolent course (slow onset) with an emphasis on extrapulmonary symptoms; . Common pathogens include mycoplasma, legionella, chlamydiae, and viruses such as RSV, influenza, CMV, and adenovirus.
- Low-grade fever
- Non-productive, dry cough
- Common extrapulmonary features include fatigue, headaches, sore throat, myalgias, malaise
- Auscultation often unremarkable
A clear distinction between typical and atypical pneumonia is not always possible based solely on the symptoms. As both forms may be caused by any pathogen, the distinction has little bearing on therapeutic decisions!
- Definition: Aspiration is the inhalation of foreign material into the respiratory tract. It often occurs after instrumentation of the upper airways or esophagus (e.g., upper GI endoscopy), or secondary to vomiting and regurgitation of gastric content.
- Risk factors
- Pathogens: mixed infections with anaerobic organisms are common (e.g., Klebsiella)
- Clinical findings
- ↓ PaO2, pH < 7.35, PaCO2 > 45 mm Hg) (
- Radiologic imaging: The lung region in which the infiltrates are seen in depends on the patient's position on aspiration. ; :
- Prevention: optimize therapy and/or prophylaxis of underlying causes to reduce the risk of aspiration
- One of the most common causes of atypical pneumonia
- More common in young individuals
- Outbreaks may occur in schools, colleges, prisons, and military facilities
- Generalized papular rash,
- Treatment: macrolides, doxycycline, and fluoroquinolones
- Legionnaires’ disease
- Pneumocystis pneumonia
- Various viral infections (e.g., adenovirus, CMV) , ,
- Pseudomonas aeruginosa: causes ventilator associated pneumonia
- Definition: a localized collection of pus and necrotic tissue within lung parenchyma caused by microbial infection
- Risk factors
- Clinical findings: indolent presentation with symptoms that evolve over weeks to months
- Pathogen detection
- Lobar pneumonia: extensive opacity restricted to one pulmonary lobe; positive air bronchogram ; unilateral pleural effusion may be visible
- Bronchopneumonia: poorly defined patchy infiltrates scattered throughout the lungs, air bronchogram is unusual
- Atypical or interstitial pneumonia: diffuse reticular opacity, absent (or minimal) consolidation
A newly developed pulmonary infiltrate on chest x-ray in a patient with the classic symptoms of pneumonia confirms the diagnosis!
- Indications: inconclusive chest x-ray, recurrent pneumonia
- Advantages: more reliable evaluation of circumscribed opacities, pleural emphysema, or sites of colliquation
Typical pneumonia usually appears as a lobar pneumonia on x-ray, while atypical pneumonia tends to appear as interstitial pneumonia. However, the underlying pathogen cannot be conclusively identified based on the imaging results!
The following tests are not part of the initial diagnostic workup; they are predominantly used for further investigation if the results of previous tests are negative or inconclusive.
- Sputum : testing for multiresistant pathogens ; severe, rapid progressive nosocomial pneumonia
- Bronchoscopy: indicated to visualize and biopsy a central mass discovered on CT imaging, or if CT results are inconclusive
Criteria for hospitalization
- Based on CURB-65 score
- Confusion (disorientation, impaired consciousness)
- Urea > 7 mmol/L (20 mg/dL)
- Respiratory rate ≥ 30/min
- Blood pressure: systolic BP ≤ 90 mm Hg or diastolic BP ≤ 60 mm Hg
- Age ≥ 65 years
Any patient being treated in a primary care setting should be reexamined after 48–72 hours to evaluate the efficacy of the prescribed antibiotic!
- Sufficient rest (not absolute bedrest) and physical therapy
- High liquid intake (prevents dehydration, reduces bronchial secretion viscosity)
- Pulse oximetry monitoring
- Oxygen via nasal tube in cases of hypoxia
- Antipyretics, analgesics (e.g., acetaminophen, ibuprofen)
- Expectorants and mucolytics
- Antitussives (e.g., codeine)
As laboratory results with definite pathogen identification may take time to obtain, initial empiric antibiotic treatment with broad coverage is recommended.
|Outpatient treatment|| |
|Inpatient treatment|| |
|Special cases|| |
Antibiotic treatment may be terminated 2–3 days after the fever subsides. In cases of community-acquired pneumonia that can be treated in the outpatient setting, seven days of antibiotic treatment are usually sufficient!
|Low/moderate risk of mortality||Patients without risk factors for multiresistant pathogens|
|Patients with risk factors for multiresistant pathogens*|
|High risk of mortality or history of recent IV antibiotic use (< 90 days)|| |
- Start empiric antibiotic therapy (see treatment of pneumonia).
- Evaluate and treat sepsis if present (see sepsis).
- Administer supplemental oxygen if patient is hypoxemic.
- Consider further diagnostic evaluation. 
- Thoracentesis if a large parapneumonic effusion is present
- Consider bronchoscopy and BAL if uncommon pathogens are suspected (e.g., tuberculosis), if a noninfectious cause is suspected, if a viral infection may be the underlying cause, or if the patient doesn't respond to treatment.
- Antipyretic therapy (e.g., acetaminophen )
- IV fluids
- Calculate the CURB65 score to identify patients who would benefit from admission.
- Consider ICU admission for severe pneumonia.
- Continuous pulse oximetry
- Parapneumonic pleuritis
- Parapneumonic pleural effusion (common)
- Respiratory failure,
We list the most important complications. The selection is not exhaustive.
- Stop smoking