الفهرس 
Etio-pathology of device-related infectionsOnly 14 pages are availabe for public view
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Abstract
Between 5% - 15% of all hospitalized patients around the world will develop an Hospital Acquired Infection during their hospital stay. An estimated 60% of these infections are thought to be related to the use of invasive devices. The paradox here is uncanny: these devices are both life-saving and life- threatening. The most commonly occurring device-related infections are ventilator-associated pneumonias (VAP), catheter related bloodstream infection (CRBSI) and catheter-associated urinary tract infections (CAUTI).
A device related infection is defined as a host immune response to one or more microbial pathogens on an indwelling implant. An understanding of the pathogenesis of these infections provides a rationale for management. Development of device-related infections begins with colonization of the foreign material, followed by a complex metamorphosis by the microorganisms with resultant biofilm formation. In this surface-associated form, bacteria have altered phenotypic properties. This change, in conjunction with the physical protective layer provided by the biofilm, renders antimicrobial therapy ineffective when used alone.
Ventilator-associated pneumonia (VAP) is the most common nosocomial infection in the intensive care unit and is associated with major morbidity and attributable mortality. The major route for acquiring VAP is oropharyngeal colonization by the endogenous flora or by pathogens acquired exogenously from the intensive care unit environment. The stomach represents a potential site of secondary colonization and reservoir of nosocomial Gram-negative bacilli. Endotracheal-tube biofilm formation may play a contributory role in sustaining tracheal colonization and also have an important role in late-onset VAP caused by resistant organisms. Aspiration of microbe-laden oropharyngeal, gastric, or tracheal secretions around the cuffed endotracheal tube into the normally sterile lower respiratory tract results in most cases of VAP.
Clinical criteria, used in combination, may be helpful in diagnosing VAP; however, the considerable inter-observer variability and the moderate performance should be taken into account. Bacteriologic data do not increase the accuracy of diagnosis as compared to clinical diagnosis. Quantitative cultures obtained by different methods, including BAL, mini-BAL or PSB seem to be rather equivalent in diagnosing VAP.
Catheter-related bloodstream infection is defined as the presence of bacteraemia originating from an i.v. catheter. It is one of the most frequent, lethal and costly complications of central venous catheterization. It is also the most common cause of nosocomial bacteraemia.
Diagnosis of CRBSI is based on the following, signs of catheter insertion site infection, clinical symptoms and signs of Bacteraemia, resolution of the symptoms and signs of bacteraemia after removal of the suspect CVC, positive blood culture; and growth of the same organism from the catheter. In practice, a presumptive diagnosis of CRBSI is often made on the basis of one or two of these criteria. The ‘gold standard’ is the combination of a positive blood culture with the same organism isolated from the catheter.
Catheter-associated urinary tract infection (CAUTI) remains one of the most common types of hospital-acquired infections. Bacteria may enter the bladder through contamination of the tip during insertion with the flora of the distal urethra or from bacteria ascending the outside or the inside of the catheter. Residual urine in the bladder of catheterised patients increases the risk of bacteriuria. During the process of infection, bacteria need first to adhere to the epithelial cells of the urinary tract and/or the surface of the catheter. They will then develop into biofilms on the catheter surface and are resistant to the immune system and antibiotics. Catheters by themselves may cause immediate physical damage to the bladder epithelium; they may be toxic and also cause inflammation. Bacteria can also damage the epithelium and cause inflammation and the combination of both may be synergistic in producing symptoms in the patient. Most episodes of catheter-associated bacteriuria are asymptomatic but it is not known why some patients are symptomatic and others are not. Further research into the pathogenesis of CAUTI needs to be carried out.
The device related infections prevention includes the ability to accurately identify, measure and analyze the cases. It also includes the provision of regular feedback to clinicians and the standardized use of evidence-based interventions.
Strategies to eradicate oropharyngeal and/or intestinal microbial colonization, such as with chlorhexidine oral care, prophylactic aerosolization of antimicrobials, selective aerodigestive mucosal antimicrobial decontamination, limitation of usage of H2 antagonists for stress ulcer prophylaxis, and measures to prevent aspiration, such as semirecumbent positioning or continuous subglottic suctioning, have all been shown to reduce the risk of VAP. And in central-line insertion, these strategies have included appropriate hand hygiene, adequate skin preparation, use of maximum sterile barriers, and site-specific dressings.
Use of these measures is routinely guided by a standardized checklist. The interventions are important individually and are recognized in the scientific literature for their collective ability to eliminate intrinsic and extrinsic patient risk, subsequently reducing device related infections incidence.
Device use and infection prevention are not mutually exclusive. Standardization of practice and empowerment are simple measures that can be applied in any setting and in any country regardless of its affluence or healthcare system. These simple measures will be crucial as the world predictably increases its use and range of devices in the provision of healthcare.
The onset and clinical manifestations of device-related infections vary with the pathogen involved, as well as which component of the device is affected. The time period after device implantation that signs and symptoms develop can assist in the selection of empiric antimicrobial therapy. Optimal diagnostic microbiologic specimens are paramount in tailoring the antimicrobial therapy, which almost always has to be given for a prolonged period of time.
The recent guidelines and publications increased our awareness of the problem of CAUTI but left significant gaps in our knowledge. Of particular concern is how little recent evidence supports our current treatment strategies for CAUTI. This deficit arose in part because only recently has the distinction between CA-ASB and CAUTI entered general awareness. We now need new trials with appropriate focus on symptomatic CAUTI to determine how long to treat this infection. Therefore, the problem of how to manage catheter-associated bacteriuria and CAUTI will become even more relevant in coming years. Ideally the unanswered questions in this field will be an inspiring challenge for the current and future generations of clinical investigators.