Clinical and microbiological characteristics of anaerobic bacteremia during 1994-2019: A Danish population-based...

Bacteremia with anaerobic bacteria is generally a marker of severe prognosis. However, population-based data is lacking. Our aim was to describe the epidemiology and the 30-day mortality rate of anaerobic bacteremia in a Danish population-based setting.

In this population-based cohort study, all first-time episodes of anaerobic bacteremia from the North Denmark Bacteremia Research Database during 1994-2019 were identified. Information on comorbidities, discharge diagnoses, and mortality was retrieved. 30-day mortality rates were calculated and a multivariate logistic regression analysis to identify risk factors for death was performed.

1750 episodes with anaerobic bacteremia were identified, corresponding to an incidence rate of 12.5 per 100,000 inhabitants (increasing from 11.2 in 1994-2014 to 17.7 in 2015-2019). Of these episodes, a third were polymicrobial, and the majority (70 %) of patients had one or more comorbid conditions. Abdominal infection was the source of bacteremia in 61 % of patients, while it was unknown for 15 %. The most frequently isolated genera were Bacteroides (45 %), Clostridium (20 %) and Fusobacterium (6 %). The overall crude 30-day mortality rate was 27 %, but rates were even higher for patients of high age, with liver disease, and solid tumors. The odds ratio (OR) for 30-day mortality was 1.32 for Clostridium species, and 1.27 for polymicrobial bacteremia with aerobic bacteria.

The incidence rate of anaerobic bacteremia increased, and the 30-day mortality rate remained high during the study period. Multiple factors influence 30-day mortality rates, including high age, liver disease, solid tumor, polymicrobial bacteremia, and bacteremia with Clostridium species.