Coagulase-negative staphylococcal contamination of whole blood and its components: the effects of WBC reduction

BACKGROUND: Most bacteria present in blood components are normal skin flora , particularly Staphylococcus epidermidis and other coagulase-negative stap hylococci. Growth patterns of these bacteria and the effects of different m ethods of component preparation may depend on variations in behavior betwee n different isolates of the same species. STUDY DESIGN AND METHODS: Whole-blood units were inoculated with 19 differe nt coagulase-negative staphylococcus (CNS) isolates at 1 to 10 and 10 to 10 0 CFUs per mL. After overnight holding at 22 degreesC, the units were proce ssed into components. The components were cultured before inoculation and d uring processing, including before and after WBC reduction. RESULTS: At low inoculum levels, CNS was detected in 15 (79%) of 19 whole-b lood units and in 12 (63%) of 19 RBCs after separation; after filtration, b acteria were detected in 3 (16%) of 19 (p = 0.0069). For platelet concentra tes, 6 (32%) of 19 grew bacteria before filtration and 1 of 18 after filtra tion (difference not statistically significant). Three (16%) of 19 plasmas were positive before and after freezing. At high inoculum levels, 16 (89%) of 18 whole-blood samples and RBCs were positive before filtration; 6 (33%) of 18 RBCs were positive after filtration (p = 0.0002); 8 (44%) of 18 plat elets were positive before filtration; 3 (17%) of 18 were positive after fi ltration (difference not statistically significant), and 7 (37%) of 18 plas ma samples were positive before and after freezing. CONCLUSION: The growth characteristics of CNS in blood components vary with differences either in the subtype of bacteria or in the donor blood. Filtr ation reduces but does not eradicate contamination of RBCs and platelets by CNS. Plasma may act as a reservoir for CNS infection.