Bottom line: While Enterococcus sp. can be a contaminant in blood cultures, it is more often a true pathogen in bacteremia and can be very harmful if untreated.
Pien BC, et al. The clinical and prognostic importance of positive blood cultures in adults. Am J Med. 2010 Sep;123(9):819-28.
Multicenter study of 2,270 episodes of positive blood cultures in 1,706 hospitalized patients January-December 2004. RESULTS: Table 2 summarizes findings of the isolates. Enterococcus spp. are associated with 128 (9%) of all blood cultures confirmed as cause of true bloodstream infection. These 128 episodes where Enterococcus spp. were identified as pathogens represented 63% of the Enterococcus spp. isolates. In 23 (11%) cases, Enterococcus spp. were identified as a contaminant, while the clinical significance was unknown for the remaining 52 (26.6%) cases. These results are similar to an earlier study of the same group of hospitals.
Weinstein MP, et al. The clinical significance of positive blood cultures in the 1990s: a prospective comprehensive evaluation of the microbiology, epidemiology, and outcome of bacteremia and fungemia in adults. Clin Infect Dis. 1997 Apr;24(4):584-602.
Study of 843 episodes of positive blood cultures January-December 1992 in 707 patients with septicemia in three teaching hospitals. RESULTS: Table 1 summarizes findings of isolates. Enterococcus spp. were among the most common pathogens; in 93 cases of Enterococcus spp. as identified isolate, it was identified as a pathogen, in 65 (69.9%) cases, and identified as a contaminant in 15 (16.1%) cases with remaining 13 cases of unknown clinical significance.