Healthcare-Associated Infections _ ______________________________________________________________
found on healthcare equipment have primarily been S. aureus , including MRSA; Pseudomonas spp.; Acinetobacter spp.; and Pasteurella spp. [115]. Washing stethoscopes with either an ethanol-based cleanser or isopropyl alcohol pads significantly reduces bacterial growth, even that of MRSA [116; 117; 118]. Contamination of therapeutic ultrasound transducer heads and ultrasound gels were evaluated in another study, and the rate of contamination was 27% for the heads and 28% for the gels [119]. The transducer heads had low levels of contamina- tion, and most of the micro-organisms were normal flora; however, high levels of contamination were found in the gels, and the micro-organisms included such pathogens as Stenotro- phomonas maltophilia , S. aureus , Acinetobacter baumannii , and Rhodotorula mucilaginosa . In two other studies, contamination of dermatoscopes was evaluated. One study indicated coloni- zation of only nonpathogenic bacteria and the other showed that use of an alcohol-based antibacterial gel as immersion fluid yielded no bacterial growth [120; 121]. Ward-based computer terminals have also been shown to have low levels of contamination. In a study of two hospitals, MRSA was found on one of 13 computer terminals in one hospital and on five of 12 in another hospital. The rate of MRSA transmission was significantly higher at the hospital with the greater number of contaminated computers [122]. In summary, a high rate of micro-organism colonization has been found on equipment within the hospital setting, but contamination is usually at low levels and the risk of direct infection is low. In general, the findings of studies have sug- gested that adequate cleaning of equipment can prevent as many as one-third of HAIs [114]. Implanted Devices Surgically implanted devices are a major source of HAI, and the development and use of intracardiac devices, orthopedic implants (prostheses and fixation devices), neurosurgical devices, cochlear implants, and breast and penile implants have increased over the past several years. The most common complication with all of these devices is infection [123; 124; 125]. The prevalence of infection associated with these devices varies, with the prevalence highest for left ventricular assist devices ( Table 5 ) [123]. Orthopedic implants, such as joint prostheses and fracture fixation devices, are associated with the lowest rate of infection, but reported mortality rates have been as high as 18% [123]. Many implanted device-related infections are caused by contam- ination during insertion, but these infections are not always the result of micro-organisms transmitted in the healthcare setting. Rather, bacteria (and sometimes fungi) colonize by adhering to the surface of the implant through the development of a biofilm [123]. Biofilms present another challenge in managing infection; biofilms provide bacteria with an extremely high level of resistance to antimicrobial agents. In fact, biofilms can tolerate antibiotic concentrations of 10 to 1,000 times of that needed to destroy free-floating (planktonic) bacteria [123]. Many bacteria, including P. aeruginosa , are capable of existing in
a planktonic state [113]. They also frequently colonize medical devices and form mono- or interspecies communities, making them more resistant to conventional drugs, often resulting in chronic infections in patients [126; 127; 128]. The CDC defines implanted device-related HAIs as those occurring within one year after implantation of a device, and the typical interval between implantation and infection varies according to the type of implant [129]. For some implants, early and late infections differ with respect to etiology and the causative micro-organisms [123; 130]. The treatment of infections related to these devices depends on the severity of the infection and the patient’s underlying condi- tion. A multidisciplinary approach involving antibiotic therapy and surgical intervention (either debridement or removal of the device) can have a substantial impact on morbidity and mortality. For example, prosthetic valve endocarditis is associ- ated with mortality rates of 42% to 100%, but the rate can be decreased 20-fold through an approach that combines medical and surgical therapy rather than medical therapy alone [123]. Empiric antibiotic therapy is usually appropriate once speci- mens have been obtained for culture, with the antibiotic agent chosen on the basis of the most common micro-organisms. TYPES OF INFECTIONS The CDC, in the NHSN, defines an infection as HAI if the date of event of the NHSN site-specific infection criterion occurs on or after the 3rd calendar day of admission to an inpatient location where day of admission to an inpatient location is calendar day 1 [130]. The diagnosis of infection is made on the basis of a combination of clinical findings and the results of laboratory studies or other diagnostic testing [130]. The NHSN provides comprehensive details about the infection criteria for 14 major types, with some further categorized into specific infection types [130]. The WHO has simplified the criteria to facilitate infection control in healthcare institutions with limited resources [18]. The rates of the five most common HAIs and the percentage each infection accounts for among all HAIs vary according to several factors, including time, geography, healthcare setting (including specific units within a hospital), and the data source. In general, catheter-related urinary tract infections are the most common, representing nearly one-third of all HAIs, and are the least costly; intravascular device-related bloodstream infections tend to be the most costly (in dollars); and ventilator-associated pneumonia is associated with the highest number of deaths ( Table 6 ) [1; 32; 78; 81; 131; 132; 133; 134; 135; 136; 137]. Other HAIs defined in the NHNS include infection of bones and joints; the central nervous system; the cardiovascular system; the eye, ear, nose, throat, or mouth; the lower respira- tory tract (other than pneumonia); the reproductive tract; skin and soft tissue; and systemic infection. Many of these other HAIs develop as complications of surgically implanted devices [123].
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