OUTBREAK OF VANCOMYCIN-RESISTANT, AMPICILLIN-RESISTANT, AND AMINOGLYCOSIDE-RESISTANT ENTEROCOCCUS-FAECIUM BACTEREMIA IN AN ADULT ONCOLOGY UNIT

An outbreak of bacteremia caused by Enterococcus faecium with high-lev el resistance to vancomycin (MIC of greater than or equal to 256 mu g/ ml), ampicillin (MIC of greater than or equal to 64 mu g/ml), and gent amicin or streptomycin (MIC of greater than or equal to 2,000 mu g/ml) occurred in an adult oncology unit from June 1991 to May 1999. Active surveillance for the presence of this organism in stool or perianal c ultures was begun in September 1991. Between June 1991 and May 1992, s even patients with bacteremia and 22 noninfected carriers of the organ ism in stool were identified. The vanA gene, tested for by PCR and gen e probe, was present in all isolates evaluated. All bacteremic patient s also had resistant E. faecium present in a stool or perianal culture ; the stool isolates tested were closely related to the respective blo od isolates as determined by pulsed-field gel electrophoresis. Antibio tic regimens using high-dose ampicillin and an aminoglycoside were ine ffective with four patients. Five patients (71%) had multiple positive blood cultures; four of these patients died. Following a multiple log istic regression analysis, it was found that bacteremic patients recei ved a significantly greater number of total antibiotic days compared w ith noninfected stool carriers (P = 0.019). The emergence of E. faeciu m with high-level resistance to vancomycin, ampicillin, and aminoglyco sides underscores the importance of performing susceptibility testing on all clinically significant isolates. In the neutropenic adult oncol ogy patient, bacteremia with this organism is of probable gastrointest inal origin, is often persistent, and is refractory to treatment with ampicillin in combination with an aminoglycoside. Prolonged use of ant ibiotics may predispose patients with gastrointestinal colonization to develop bacteremia.