What is PNA (Pneumonia)?
PNA is the medical abbreviation for pneumonia, an acute respiratory infection affecting the alveoli and distal airways that represents a major cause of morbidity and mortality worldwide, accounting for approximately 41,000 deaths annually in the United States alone. 1
Definition and Clinical Presentation
Pneumonia is diagnosed when a patient presents with two or more clinical signs or symptoms of infection combined with radiographic evidence of air space disease 1:
Clinical Signs:
- Temperature >38°C or ≤36°C
- Leukocyte count <4,000/μL or >10,000/μL 1
Clinical Symptoms:
- New or increased cough
- Dyspnea (shortness of breath)
- Sputum production
- Chest pain
- Pleuritic pain 2
Radiographic Findings:
- Air space density on chest imaging without alternative explanation 1
Epidemiology and Impact
Pneumonia results in substantial healthcare burden with approximately 1.4 million emergency department visits and 740,000 hospitalizations annually in the US 1. Up to 10% of patients with community-acquired pneumonia require hospitalization, and of those hospitalized, up to 1 in 5 require intensive care 1.
High-Risk Populations
Patients at highest risk for pneumonia and its complications include:
- Older adults (≥65 years)
- Those with underlying lung disease
- Current smokers
- Immunosuppressed individuals 1
These populations face increased risk for severe complications including sepsis, acute respiratory distress syndrome, and death 1.
Causative Organisms
Only 38% of hospitalized pneumonia patients have a pathogen identified 1. Among those with identified pathogens:
- Up to 40% have viral etiologies
- Approximately 15% have Streptococcus pneumoniae (the most common bacterial cause)
- Other bacteria, fungi, and atypical organisms account for the remainder 1, 3
The causative organisms vary greatly by geography and include bacteria, respiratory viruses, fungi, and atypical pathogens such as Mycoplasma pneumoniae, chlamydiae, and Legionella pneumophila 4, 3.
Diagnostic Approach
The American College of Radiology recommends posteroanterior (PA) and lateral chest radiographs as the initial imaging modality, with sensitivity of 83.9% for detecting pneumonia 5. However, chest radiography can be normal early in disease, with typical appearances present in only about 36% of cases on initial evaluation 6.
When chest radiograph is negative but clinical suspicion remains high:
- Consider chest ultrasound (sensitivity 93-96%, specificity 93-96%) 5, 6
- CT chest may be warranted in patients who cannot reliably follow-up or for whom delayed diagnosis could be life-threatening 2
- CT detects pneumonia in 27-33% of patients with negative chest radiographs and clinical suspicion 6
Clinical Significance
The primary diagnostic challenge is distinguishing self-limited viral infections from bacterial pneumonia requiring antibiotic therapy 2. This distinction is crucial because it determines whether patients benefit from antibiotics and reduces inappropriate antibiotic use in viral respiratory illnesses 2.
Important caveat: A normal chest X-ray does not rule out pneumonia, as radiographic changes may not develop until later in the disease course 6. The World Health Organization confirms that chest X-ray may be normal early in pneumonia 6.