Invasion of the blood- stream with a microbial species that has the pathogenic potential to colonize this site can then result in IE. Transient Bacteremia Mucosal surfaces are populated by a dense endogenous microflora. Trauma to a mucosal surface, particularly the Table 2. Primary Reasons for Revision of the IE Prophylaxis Guidelines IE is much more likely to result from frequent exposure to random bacteremias associated with daily activities than from bacteremia caused by a dental, GI tract, or GU tract procedure. Prophylaxis may prevent an exceedingly small number of cases of IE, if any, in individuals who undergo a dental, GI tract, or GU tract procedure. The risk of antibiotic-associated adverse events exceeds the benefit, if any, from prophylactic antibiotic therapy. Maintenance of optimal oral health and hygiene may reduce the incidence of bacteremia from daily activities and is more important than prophylactic antibiotics for a dental procedure to reduce the risk of IE. Wilson et al Prevention of Infective Endocarditis 1739 gingival crevice around teeth, oropharynx, GI tract, urethra, and vagina, releases many different microbial species tran- siently into the bloodstream. Transient bacteremia caused by viridans group streptococci and other oral microflora occurs commonly in association with dental extractions or other dental procedures or with routine daily activities. Although controversial, the frequency and intensity of the resulting bacteremias are believed to be related to the nature and magnitude of the tissue trauma, the density of the microbial flora, and the degree of inflammation or infection at the site of trauma. The microbial species entering the circulation depends on the unique endogenous microflora that colonizes the particular traumatized site. Bacterial Adherence The ability of various microbial species to adhere to specific sites determines the anatomic localization of infection caused by these microorganisms. 