Risk factors for mortality in patients with anaerobic bacteremia

Risk factors for mortality in anaerobic bacteremia have been incompletely defined. The aims of the present study were to determine clinical significance by pathogen for a broad range of obligate anaerobic organisms isolated from blood, and to define the factors independently associated with mortality among those with clinically significant bacteremia. All patients who had anaerobic bacteria isolated from blood over a 19-month period (from 1 September 1998 to 1 April 2000) at two urban teaching hospitals were included in this study. Each case was analyzed for clinical significance by means of a retrospective medical record review using predetermined definitions. Information was collected on a broad range of clinical and microbiological factors, which were evaluated for their association with mortality using a Cox proportional hazards model. Among 166 patients with obligate anaerobic bacteria isolated from blood, 73 (44%) were deemed to have clinically significant bacteremia. Clinical significance ranged from 0% (0/53) for Propionibacterium spp. to 96% (43/45) for Bacteroides spp. The crude mortality rate in patients with clinically significant anaerobic bacteremia was 25% (18/73). Mortality was significantly associated with age, polymicrobial infection, and underlying heart, kidney or liver disease in univariate analysis. Only the presence of liver disease (relative risk, 5.3; 95% confidence interval, 1.7-16.0; P=0.003) and patient age (relative risk, 1.06/y; 95% confidence interval, 1.0-1.1; P=0.005) remained significant in multivariate analysis. Among patients with anaerobic bacteremia, clinical significance varies markedly by pathogen and mortality is independently associated with age and underlying liver disease.