Pseudomonas aeruginosa, a gram- negative bacteria, can cause pneumonia, an acute inflammation of the lungs. It can be primary, following aspiration of the bacteria e.g. in patients who are being mechanically ventilated or can be the result of bacteremic spread to the lungs.
P. aeruginosa colonization can occur in airways damaged due to mechanical ventilation or a preceding viral infection, or trauma and is usually followed by acute pneumonia, sepsis, and death. As an etiology of ventilator-associated pneumonia, P. aeruginosa has a high mortality rate compared to other organisms . The incidence of P. aeruginosa pneumonia is increased in patients with chronic obstructive pulmonary disease (COPD), nursing home residents, and patients recently discharged from a hospital .
Patients aged over 65 are at an increased risk for mortality from the bacteremic pneumococcal disease. In elderly persons, the expression of common signs and symptoms of pneumonia are usually obscured, atypical, or even absent   .
Symptoms of pneumonia include a productive cough, severe dyspnea, fever, chills, cyanosis, confusion, and signs of systemic inflammatory response. On physical examination, fever, cyanosis, rales, rhonchi, retractions, and hypoxia may be detected. In patients with cystic fibrosis, clubbing, malnutrition, and an increased anteroposterior (AP) chest diameter can develop.
If pneumonia is suspected, blood gas analysis to assess the presence of hypoxia or hypercarbia should be performed and sputum and respiratory secretions have to be cultured. However, isolating Pseudomonas from tracheal secretions and sputum may reveal airway colonization. Sputum has a poor sensitivity and specificity for identifying the bacterial etiology of pneumonia, therefore in patients who are on mechanical ventilation quantitative cultures are obtained through bronchoalveolar lavage and specimen brushings.
Community-acquired pneumonia is diagnosed by clinical presentation (e.g. fever, cough, pleuritic chest pain) and by observing infiltrates on chest radiography. Sputum and blood cultures are rarely useful for outpatients and usually ordered for severely ill inpatients .
A chest radiography with lateral and posteroanterior views  may show focal or diffuse opacities but in immunosuppressed patients, especially those suffering from diabetes, uremia, neutropenia or alcoholism, the appearance of the infiltrates can be delayed. Other findings on the radiograph suggestive of pneumonia include parapneumonic effusions, air bronchograms, and the silhouette signs. P. aeruginosa has a predilection for lower lobes of the lungs. The involvement may be bilateral and extensive, or unilateral. Massive consolidation can occur but has a poor prognosis. Patchy bronchopneumonia, necrosis, abscess formation, and nodular infarcts are other possible findings. Complications of pneumonia such as atelectasis or lung abscesses may also be detected. In patients with existing structural lung diseases, the appearance of the signs of pneumonia on radiography will not be straightforward.
The use of computed tomography (CT) scan has increased in clinical practice, but its usefulness in assessing pneumonia has been questioned with various reports suggesting that CT scan should be limited to the following settings: