Pneumonia is defined as the infection of the distal airways, air sacs, or both.

Classification of community-acquired pneumonia:

If the patient was previously well or is under 65 years of age (or both): Streptococcus pneumoniae (pneumococcal) and Mycoplasma are the most common causes in younger healthy adults; also, less frequently, Chlamydia pneumoniae and Hemophilus influenzae

If the patient has comorbid illness or is 65 years of age or older (or both): Hemophilus influenzae, Klebsiella pneumoniae, Legionella pneumophila, Moraxella catarhalis, Mycobacterium tuberculosis, Staphylococcus aureus and, less commonly, Streptococcus pneumoniae

Viral pneumonia is uncommon except in outbreaks of influenza A and respiratory syncytial virus or as a complication of atypical measles.

Cytomegalovirus and herpes simplex viruses are treatable causes of pneumonia in immunocompromised patients.

Pneumocystis carinii pneumonia may occur in immunocompromised patients, especially those with HIV or AIDS.

Aspiration of oral pharyngeal secretions, gastric contents or chemicals may predispose a patient to bacterial pneumonia. Those at risk for this problem include alcoholic people, elderly people, those who have difficulty swallowing, those with motility or neuromuscular disorders, and stroke victims.

No cause is identified in approximately one-third to one-half of all cases

Symptoms
- fever, chills
- cough
- sputum may be yellow, green, blood-tinged
- chest pain: sharp, localized pleuritic chest pain is seen in acute lobar type only
- shortness of breath may be present

Physical findings
- temperature elevated
- heart rate elevated
- respiratory rate increased
- oxygen saturation decreased
- may or may not appear acutely ill
- flushed, diaphoretic if fever is high
- may "splint" the affected side if there is pleuritic pain
- variable level of respiratory distress
- dullness on percussion if there is consolidation
- air entry may be decreased
- inspiratory crackles
- wheezes may be present
- bronchial breathing
- pleural rub may be present (rarely)

In elderly or chronically ill clients, the clinical presentation of the various types of pneumonias is often atypical or obscured. Overt respiratory signs may be absent.
They may present with deterioration of preexisting medical problems, changes in level of consciousness, confusion, or functional impairment, such as loss of energy, a decrease in appetite or vomiting. These clients are at increased risk of death from bacterial pneumococcal disease.

Adapted from Clinical Practice Guidelines for Nurses in Primary Care. Respiratory System. Internet. Accessed on August 31, 2009.