Postoperative peritonitis carries a higher risk of complications and mortality than does community-acquired disease. Little, however, is known about the specific microbiology of this condition. To gain insight into this problem, the microbiological findings of 67 patients with postoperative peritonitis were compared with those of 68 patients with community-acquired peritonitis. In a comparison of postoperative peritonitis with community-acquired disease, the number of isolates of enterococci (23 versus 6) and Enterobacter species (13 versus 4) were increased and the number of isolates of Escherichia coli (21 versus 42) were reduced. Antibiotic therapy before reintervention increased the number of resistant organisms at relaparotomy (33% versus 8%). The in vitro efficacy of the primary antibiotic or combination of drugs did not affect mortality rates (40% versus 38% after effective and ineffective treatment, respectively). Thus, the microbiology of postoperative peritonitis differs significantly from that of community-acquired disease, and specific antibiotic therapy is required, despite the doubtful impact on survival.

Background The microbiology of secondary peritonitis is well known and standards of antibiotic therapy are established. In contrast, little is known about the bacteriology of postoperative peritonitis. Resistant strains could be involved and patients may have had previous antibiotic treatment. Methods The intraoperative and postoperative bacteriology (10 days after operation) of all 88 cases of postoperative peritonitis occurring between September 1994 and May 1999 were documented. Resistances were used to determine effective antibiotic therapy. Results Compared with secondary peritonitis, enterococci outnumbered Escherichia coli in postoperative peritonitis. While E. coli showed no advanced resistance, the different pattern of bacterial findings (e.g. enterococci, Enterobacter, Gram‐positive bacteria) leads to failures of standard therapy for secondary peritonitis. Imipenem–cilastatin failed in 20 per cent, piperacillin–tazobactam in 31, aminoglycosides in 31, ciprofloxacin in 37 and third‐generation cephalosporins in 47 per cent (the latter three combined with metronidazole). Conclusion Cephalosporins, the ‘gold standard’ in secondary peritonitis, fail in postoperative cases. Carbapenems are the drugs of choice. Aminoglycosides should be avoided in these patients. © 2000 British Journal of Surgery Society Ltd