Background: Intra-abdominal infections (IAI) are a major cause of hospital morbidity and mortality. However, due to the multi-factorial nature of IAI, treatment failure and mortality have been difficult to reliably predict. We hypothesize that specific infecting organisms predict mortality independent of all other patient factors.

Patients and Methods: All patients with non-appendiceal IAI treated at an academic tertiary care facility over 8 years (June 1999-June 2007) were included. Data collected included demographics, comorbidities, source of infection, intra-abdominal culture results, type of infection (community vs nosocomial), type of intervention (operation vs percutaneous drainage), and mortality. Charlson Comorbidity Index and multiple organ dysfunction score (MODS) were evaluated.

Results: 323 patients had an overall mortality of 8.7%. Intra-abdominal cultures were obtained on 303 (93.8%) patients. The mean age was 54 and 50% were male. The most common etiology of IAI was post-operative infections (44%). There were 49 distinct species isolated. The most common organisms were: Enterococcus species (93), E. Coli (75), Pseudomonas Aeruginosa (38), Candida Albicans (35), and Bacteroides Fragilis (34). Twenty-five cultures (8.3%) had no growth, 35.6% grew one organism, 20.1% grew two organisms, 20.1% grew three organisms, 11.6% grew four organisms, 12 (4.0%) grew 5 organisms, and 1 (0.3%) grew six organisms. Bivariate analysis revealed multiple risk factors associated with mortality (see table).

Risk Factors	No Mortality (N=295)	Mortality (N=28)	p-value
Age ≥ 65	26%	61%	<0.001
Charlson score ≥ 2	23%	68%	0.031
Operative Management	75%	96%	0.008
Vent > 72 hours	27%	57%	0.001
Cardiac Event	10%	54%	<0.001
CRBS Infection	12%	54%	<0.001
Pre-op MODS ≥ 4	21%	43%	0.016
POD#7 MODS ≥ 4	17%	54%	<0.001
Needed re-intervention	23%	46%	0.01
Pneumonia	17%	39%	0.006
More than one species	55%	63%	NS
Colon Etiology	29%	39%	NS
Bacteroides Species (Non B. Fragilis)	4%	19%	0.008
P. Aeruginosa	11%	26%	0.059
Enterococcus (VRE + Faecalis + Faecium)	10%	30%	0.008
C. Perfringens	3%	11%	0.05

Logistic regression demonstrated that independent risk factors for mortality were Age ≥ 65 (OR=2.92), cardiac event (OR=5.50), catheter-related bloodstream infection (OR=7.63), the presence of Bacteroides species (non B. Fragilis) (OR=7.37), and Enterococcus (VRE + Faecalis + Faecium) (OR=5.67). The C statistic was 0.89.

Conclusion: These results demonstrate that in addition to age and intrinsic patient factors, the presence of specific bacterial organisms independently predicts mortality in patients with IAI.