Pseudomonas pneumonia: a prototype of hospital-based infection

Thin-section CT findings in Pseudomonas aeruginosa pulmonary infection

OBJECTIVE

The aim of this study was to assess clinical and pulmonary thin-section CT findings in patients with acute Pseudomonas aeruginosa (PA) pulmonary infection.

METHODS

We retrospectively identified 44 patients with acute PA pneumonia who had undergone chest thin-section CT examinations between January 2004 and December 2010. We excluded nine patients with concurrent infections. The final study group comprised 35 patients (21 males, 14 females; age range 30-89 years, mean age 66.9 years) with PA pneumonia. The patients' clinical findings were assessed. Parenchymal abnormalities, enlarged lymph nodes and pleural effusion were evaluated on thin-section CT.

RESULTS

Underlying diseases included malignancy (n=13), a smoking habit (n=11) and cardiac disease (n=8). CT scans of all patients revealed abnormal findings, including ground-glass opacity (n=34), bronchial wall thickening (n=31), consolidation (n=23) and cavities (n=5). Pleural effusion was found in 15 patients.

CONCLUSION

PA pulmonary infection was observed in patients with underlying diseases such as malignancy or a smoking habit. The CT findings in patients with PA consisted mainly of ground-glass attenuation and bronchial wall thickening.

ADVANCES IN KNOWLEDGE

The CT findings consisted mainly of ground-glass attenuation, bronchial wall thickening and cavities. These findings in patients with an underlying disease such as malignancy or a smoking habit may be suggestive of pneumonia caused by PA infection.

Intensive-care unit lung infections: The role of imaging with special emphasis on multi-detector row computed tomography

Nosocomial pneumonia is the most frequent hospital-acquired infection. In mechanically ventilated patients admitted to an intensive-care unit as many as 7-41% may develop pneumonia. The role of imaging is to identify the presence, location and extent of pulmonary infection and the presence of complications. However, the poor resolution of bedside plain film frequently limits the value of radiography as an accurate diagnostic tool. To date, multi-detector row computed tomography with its excellent contrast resolution is the most sensitive modality for evaluating lung parenchyma infections.

Animal models of pulmonary infection in the compromised host: potential usefulness for studying health effects of inhaled particles

Pulmonary infection leading to pneumonia is a significant cause of morbidity and mortality worldwide. Airborne particles have been associated with pneumonia through epidemiological research, but the mechanisms by which particles affect the incidence of pneumonia are not well established. The purpose of this review is to examine the potential of animal models to improve our understanding of the mechanisms by which inhaled particles might affect the incidence and resolution of pulmonary infection. The pathogenesis of pneumonia in most animal models differs from that in humans because humans frequently have underlying diseases that predispose them to infection with relatively low doses of pathogens. Normal, healthy animals lack the underlying pathology often found in humans and clear bacteria and viruses rapidly from their lungs. To overcome this, animals are administered large inocula of pathogens, are treated with agents that cause mucosal lesions, or are treated with immunosuppressive drugs. Alternatively, pathogenic bacteria are protected from phagocytosis by encasing them in agar. No one animal model will replicate a human disease in its entirety, and the choice of model depends upon how well the animal infection mimics the particular human response being examined. The advantages and disadvantages of animal models in current use for bacterial and viral infections important in the etiology of human pneumonia are reviewed in detail. Considerable data indicate that prior exposure to particles compromises the ability of experimental animals to resolve a subsequent infection. In addition, information is available on the effects of particle exposure on various portions of respiratory defense including phagocytic function, ciliary movement, inflammation, and antibody response in the absence of infection. In contrast, little research to date has examined the consequences of particle exposure on the host defense mechanisms of animals already infected or on their ability to resolve their infection.

Opportunistic pneumonia

Patients with abnormalities in their immune defense mechanisms are frequently encountered in the practice of medicine. These patients have increased susceptibility to infections that often involve the lung. Many of these infections are caused by opportunistic organisms that typically do not produce disease in individuals with a normally functioning immune system. To complicate the evaluation of these patients, they frequently develop noninfectious lung disease, which can have a radiographic appearance that is similar to infection. The purpose of this article is to present an approach to the evaluation of chest radiographic abnormalities in the immunocompromised patient with suspected pneumonia. Clinical information that is pertinent in the evaluation of immunocompromised patients is discussed. The various chest radiographic patterns seen in both infectious and noninfectious diseases that occur in the immunocompromised patient are reviewed. Integration of clinical information and radiographic findings in the development of a list of differential diagnoses is stressed.

Lung mechanics, gas exchange, pulmonary perfusion, and hemodynamics in a canine model of acute Pseudomonas pneumonia

Acute bilateral hemorrhagic pneumonia was induced in 6 dogs (pneumonia group) by endotracheal inoculation with Pseudomonas aeruginosa. Measurements of lung mechanics, gas exchange, distribution of pulmonary blood flow, and hemodynamics were made prior to inoculation and 5 hr later when pneumonia was established. These findings were compared to the same measurements in 6 other dogs inoculated with a sterile broth (control group). While there were no significant changes in lung mechanics in the control group, pneumonia caused a significant and proportional reduction (42%) in total lung capacity (TLC) and functional residual capacity (FRC). Although tidal lung compliance was reduced in the pneumonia group, neither the specific compliance nor the deflation pressure-volume curve, with lung volume expressed as a percentage of observed TLC, changed significantly. Pneumonia caused marked hypoxemia with a mean increase in shunt and venous admixture of 35% and 52%, respectively, while the control group developed only minimal abnormalities in gas exchange. Perfusion of the consolidated lung region, determined by radioactive microspheres and expressed as a percentage of total pulmonary blood flow, showed a small but significant decrease from baseline (53 +/- 13%) to established pneumonia (44 +/- 14%), while no change in lobar perfusion was seen in the control group. Only the infected animals showed significant changes in hemodynamics with a rise in cardiac output and fall in mean systemic arterial pressure and vascular resistance. We conclude that acute experimental Pseudomonas pneumonia causes reduction of FRC by filling of alveoli with inflammatory exudate and further reduction of TLC by preventing these alveoli from inflating at higher lung volumes without evidence for a change in the elastic properties of the remaining inflated lung; marked hypoxemia caused by maintenance of perfusion of consolidated lung with reduced or absent ventilation; and a hyperdynamic septic hemodynamic state similar to that seen in humans.

Pneumatocele in infants and children. Report of 12 cases

Pneumatoceles were found in 2.4 per cent of 493 infants and children with pneumonia. In all cases, attempts were made to establish the etiology by means of blood cultures and of deep tracheal aspirations or pleural punctures, when indicated. A definite cause was established in 9 of 12 cases. Seven were due to infection: in two Hemophilus influenzae was involved; two others were due to Pseudomonas aeruginosa; and Staphylococcus aureus, Klebsiella pneumoniae, and Streptococcus pneumoniae were each isolated in one case. Two pneumatoceles were seen following kerosene ingestion. A coagulase negative staphylococcus isolated only on blood culture in one other child may have been related to the illness. Two patients experienced spontaneous pneumothorax and died of progressive respiratory failure due to enlargement of the pneumatocele, but all the other patients recovered without complication. Pneumatoceles in childhood can result from a variety of bacterologic infections as well as from kerosene ingestion.

Antibody response to Pseudomonas aeruginosa exoproducts in cancer patients

We analyzed sera from 28 patients with various types of malignancies for the occurrence of antibodies against exotoxin A of Pseudomonas aeruginosa and two Pseudomonas proteases. A total of 27 of these individuals were colonized or infected with P. aeruginosa at one time or another during the study, whereas the remaining patient was colonized with four non-P. aeruginosa species of Pseudomonas. Sera were obtained from several of these patients before P. aeruginosa colonization or infection of these individuals was detected, which provided an opportunity to evaluate their responsiveness to pseudomonal exoproducts as they acquired the organism. Exotoxin A was purified from culture supernatant fluids of strain PA-103, and the two proteases were purified from an isolate of strain JR3, a highly proteolytic strain originally recovered from the sputum of a cystic fibrosis patient. Antibodies to the exotoxin A and the two proteases were detected in these sera, and sera which contained relatively high antibody levels to exotoxin A afforded mice complete protection against lethal challenges with this substance. Statistical analyses showed that patients infected with P. aeruginosa had consistently higher antibody levels (P less than 0.005) to the exoproducts than patients who were colonized with this organism. Also, patients colonized with P. aeruginosa possessed significantly higher antibody levels (P less than 0.003) to these three exoproducts than uninfected, hospitalized patients. Parke-Davis type 1 was the strain most commonly isolated from these patients (46%), but colonization or infection due to this organism usually resulted in the production of low levels of antibody to Pseudomonas exoproducts. However, infections with Parke-David type 7 organisms were always associated with intermediate- and high-responder sera to exotoxin A. These results indicated that potentially toxic products were elaborated during the course of cancer-related colonization and infection with P. aeruginosa.