Definition of pneumonia
Reading File
Finding Sources
Finding Sources
Finding Sources
Reading File
Reading File
Here is the definition of pneumonia drawn from authoritative medical textbooks:
Pneumonia - Definition
Pneumonia is an infection of the lungs that leads to consolidation of the usually air-filled alveoli. It can occur in all age groups and is caused by a wide range of organisms including viruses, bacteria, mycobacteria, mycoplasma, and fungi.
- Textbook of Family Medicine, 9e, p. 321
Key Points from the Definition
- The core pathological event is consolidation - the alveoli (normally air-filled spaces) become filled with inflammatory exudate, fluid, or debris, impairing gas exchange.
- The term "pneumonia" refers specifically to infection of the lung parenchyma, distinguishing it from bronchitis (airways only) or pleuritis (pleural lining).
- It is not a single disease but a syndrome produced by many different organisms.
Causative Agents
| Category | Examples |
|---|---|
| Bacteria | Streptococcus pneumoniae, Haemophilus influenzae, Pseudomonas, Klebsiella |
| Atypical bacteria | Mycoplasma, Chlamydia, Legionella spp. |
| Viruses | Influenza A/B, RSV, SARS-CoV-2 |
| Fungi | Pneumocystis jirovecii (PCP), Coccidioides, Cryptococcus |
| Mycobacteria | Mycobacterium tuberculosis, NTM |
Classification
Pneumonia is further classified by setting and host, because these determine likely pathogens and management:
- Community-Acquired Pneumonia (CAP) - acquired outside the hospital
- Hospital-Acquired (Nosocomial) Pneumonia (HAP) - onset ≥48 hours after hospital admission
- Health Care-Associated Pneumonia (HCAP) - in patients from nursing homes or with frequent healthcare exposure
- Ventilator-Associated Pneumonia (VAP) - occurring in mechanically ventilated patients
- Opportunistic Pneumonia - in immunocompromised hosts (HIV, transplant, chemotherapy)
Clinical Hallmarks
- Cough (productive or non-productive, possibly blood-tinged)
- Fever and chills
- Dyspnea (shortness of breath)
- Pleuritic chest pain
- On exam: decreased breath sounds, dullness to percussion, egophony over the affected area
- Elevated WBC (>15,000/mm³) with neutrophil predominance in bacterial cases
Systemic viral infections (e.g., influenza, measles, varicella) can also trigger secondary bacterial pneumonia, highlighting the overlap between viral and bacterial causes.
Source: Textbook of Family Medicine 9e, p. 321 - "Pneumonia is an infection of the lungs that leads to consolidation of the usually air-filled alveoli. It occurs in all age groups and can be caused by various agents, including viruses, bacteria, mycobacteria, mycoplasma, and fungi."
This is a shared conversation. Sign in to Orris to start your own chat.