Coagulasenegative staphylococci CoNS

NVE caused by CoNS has become increasingly more common, with most recent estimates of approximately 5-7% of all cases [239]. However, it is likely that the incidence rate will increase, due to increasing dependence of medical progress on intravascular catheters, indwelling devices, and other invasive procedures.

CoNS are a heterogeneous group of Grampositive coccal species with a clustered appearance on Gram stain and a negative reaction on tube coagulase test. In practical terms, however, the slide coagulase test is a more rapid surrogate marker of the tube coagulase test, demonstrating very good correlation, albeit with a few exceptions (see below). The CoNS are residents of the normal human skin microflora. CoNS have a propensity to cause foreign body infections because of their propensity to adhere to polymer surfaces and form biofilm [240]. Due to these properties, CoNS account for a significant portion of prosthetic valve endocarditis, discussed in chapter 11. However, in the native heart, particularly in the presence of preexisting valvular or congenital heart disease [241-243], the CoNS can cause endocarditis. In general, the clinical course and outcome of the CoNS-NVE is variable, ranging from a subacute, indolent infection with few complications to a fulminant, destructive infection, complicated by valve dysfunction, heart failure, and embolic phenomena. The difference in virulence appears to be species specific, although host factors likely contribute as well. Although S. epidermidis is the species most frequently associated with NVE, the clinical characteristics and management of certain other CoNS-NVE are also presented. It is important to note that although CoNS are considered to be low-virulence pathogens, a recent international study demonstrated that patients with CoNS-

NVE had rates of congestive heart failure and of mortality similar to, as well as rates of cardiac valvular surgery higher than, patients with NVE due to S. aureus [239]. This point emphasizes the virulent nature of these "skin flora" organisms.

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