Choosing Antibiotics for Intra-Abdominal Infections: What Do We Mean by "High Risk"?

Background: The definition of "high risk" in intra-abdominal infections remains vague. The purpose of this study was to investigate patient characteristics associated with a high risk of isolation of resistant pathogens from an intra-abdominal source. Methods: All complicated intra-abdominal and abdominal organ/space surgical site infections treated over a ten-year period in a single hospital were analyzed. Infections were categorized by pathogen(s). Organisms designated "resistant" were those that had a reasonable probability of being resistant to the broad-spectrum agents imipenem/cilastatin and piperacillin/tazobactam, and included non-fermenting gram-negative bacilli (e.g., Pseudomonas aeruginosa ), resistant gram-positive pathogens, vancomycin-resistant enterococci, and fungi. Patient characteristics were analyzed to define associations with the risk of isolation of "resistant" pathogens. Results: A total of 2,049 intra-abdominal infections were treated during the period of study, of which 1,182 had valid microbiological data. The two genera of pathogens isolated from more than 25% of health care-associated infections and more commonly than from community-acquired infections were Enterococcus spp. (29%) and Candida spp. (33%). Health care association, corticosteroid use, organ transplantation, liver disease, pulmonary disease, and a duodenal source all were associated with resistant pathogens. By multivariable analysis, several acute and chronic measures of disease were predictive of death, with a strong interaction between solid organ transplantation, resistant pathogens, and death. Other links between specific pathogens and patient characteristics were documented, for example, between fungal infection and a gastric, duodenal, or small bowel source, and between liver transplantation and vancomycin-resistant enterococci. Conclusions: On the basis of clinical characteristics, it may be possible to identify patients with intra-abdominal infections caused by pathogens that are potentially resistant to broad-spectrum antibacterial agents. Under these circumstances, and if warranted clinically, broadened coverage probably ought to include specific anti-enterococcal and anti-candidal therapy.