Molecular epidemiology of gram-negative bacteremia

We did pulsed field gel electrophoresis (PFGE) and antibiotic susceptibilit y testing on 202 gramnegative isolates obtained from blood cultures between 1 January 1989 and 31 December 1993. Seventy-eight patients had at least t wo gram-negative isolates of the same species recovered from blood drawn on e or more days apart and met the other study criteria. Twenty patients had only 1 bloodstream infection, 48 patients had 1 recurrence of bacteremia, a nd 10 patients had >1 recurrence of bacteremia. Of 80 recurrences of bacter emia, 52 (65%) were relapses and 28 (35%) were reinfections. Seventy-eight percent of the episodes of bacteremia occurring less than or equal to 300 d ays apart were relapses, and 100% occurring >300 days apart were reinfectio ns (P <.001). Organisms causing recurrent bacteremia were not more resistan t than those causing initial episodes. In conclusion, most episodes of recu rrent gram-negative bacteremia were relapses. Relapses and reinfections cou ld not be distinguished only by the length of time between episodes or by a ntimicrobial susceptibility patterns.