160 Chapter 8 Host factors associated with persistent MRSAB Clinical risk factors Numerous observational studies have identified independent patient risk factors for the development of persistent SAB (Table 1) [22–28]. A recurring theme is the presence of retained intravascular devices or foreign bodies, which are independently associated with persistent SAB [15,22,24–26,28]. Similarly, metastatic infection (including endocarditis, bone and joint infection), chronic renal failure, cirrhosis, and diabetes are also associated with persistent SAB [22,23,25,26,28]. The largest study was a nested case–control study examining risk factors for persistent SAB, performed by Chong et al., who included 483 patients with persistent SAB and 212 patients with resolving SAB [22]. In addition to the previously described risk factors, multivariate analysis revealed community-onset bacteremia, methicillin resistance, central venous catheter (CVC)-related infection, and vancomycin trough of <15 mg/L as risk factors for persistent SAB [22]. The majority of these studies do not distinguish methicillin-susceptible S. aureus (MSSA) from MRSAB, often citing vancomycin use as a risk factor for persistence [23,26]. Yoon et al. limited their investigation to MRSA only, identifying retention of implanted devices and metastatic infection of at least two sites as predictors of persistent MRSAB [24]. While these studies represent an important component in the understanding of persistent SAB and MRSAB, it currently comes as little surprise that unresolved sources of infection are the most frequently reported clinical risk factors for persistence. However, clinical risk factors only partially explain which patients develop persistent SAB.
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