Predictors of positive blood culture in an emergency service. A prospective study

Abstract number: 1733_452

Ceballos B., Peralta G., Ansorena L., Rodriguez-Lera M., Roiz M., Sánchez M.

Objectives: The microbiology laboratory is of limited usefulness for bloodstream infection detection, because only a low proportion of blood cultures have positive results, and the final results take at least 24 h to be known. We design a prospective study to develop a prediction model for bacteraemia, based on clinical data of patients assisted in an Emergency Service.

Methods: The study was developed in a 250 bed community teaching hospital placed in the North of Spain with around 65,000 presentations to the emergency service annually. All patients to whom blood cultures were performed from January to June 2006 were recruited for the study. Univariate analyses and stepwise logistic regression were performed to identify factors associated with bacteraemia.

Results: Blood cultures were performed in 390 patients in the period of study. Bacteraemia was detected in 60 (15.4%). Isolated microorganisms were E. coli in 35 (9%), S. aureus in 3 (0.8%), S. agalactiae in 2 (0.5%), P. aeruginosa in 2 (0.5%), Listeria spp. in 2 (0.5%), and others in 16 (4.1%). No significant differences among patients with positive and negative blood cultures in age, gender, proportion of comorbibities (renal chronic failure, cardiac failure, diabetes, dementia, immunosuppression, cirrhosis, neoplasia), Charlson index score, or clinical manifestations (presence of chills, or vomiting, and mean systolic blood pressure) were detected. However patients with positive blood cultures had shorter duration of the acute illness (29.3±32.5 h vs 59.4±85.7 h), more frequently had no previous antibiotic treatment (96.7% vs 84.2%), more frequently had temperature higher than 38°C (60% vs 40.2%), severe sepsis (21.7% vs 7.9%) or altered consciousness (20% vs 6.7%). In a logistic regression model the predictors of bacteraemia were absence of previous antibiotic treatment (OR: 4.87, 95CI: 1.12–21.17), altered consciousness at arrival (OR: 3.85, 95CI: 1.55–9.54) and the presence of fever (OR: 2.18, 95CI: 1.16–3.97).

Conclusions: Several clinical parameters can be useful for predict bacteraemia in an Emergency service. The absence of previous antibiotic administration, altered consciousness at arrival, and the presence of fever are associated with a higher risk of bacteraemia