An audit of blood cultures performed in an emergency department at a Johannesburg Academic Hospital

Abstract

Background: Blood cultures(BCs)are the standard test for detecting bacteraemia but have come under scrutiny on their usefulness in Emergency Departments (EDs) as they have a low yield, tend not to alter patient management and may be subject to high contamination rates especially in resource limited settings. Identifying patients most at risk of bacteraemia may improve the usefulness of BCs as investigations. We aim to describe and compare clinical and demographic characteristics of patients in whom BCs where taken as well as validate scoring systems predicting bacteraemia. Methods: A retrospective observational, descriptive and comparative study. Reports from all BCs performed in the ED in 2017 were requested from the National Health Laboratory Service (NHLS). Data from all positive BCs were used to audit cultured organisms and their sensitivity and resistance patterns. Secondly, clinical and laboratory data from 206 consecutively selected patients (103 positive and 103 negative BC results) were used to calculate the Shapiro score, a prediction tool for bacteraemia, and the Systemic Inflammatory Response Syndrome (SIRS) criteria. Results: There was a total of 4011 BCs performed in 2017. There were715 (17.8%) positive BCs, of which pathogens were cultured in 400 (10.0%) BCs and 315 (7.9%) BCs cultured known contaminants. Streptococcus Pneumoniae was the highest pathogen load (n=108, 24.3%) and was 94.4% sensitive to co-amoxiclav. A positive Shapiro score and SIRS criteria increased the likelihood of a positive BC by 5.6 and 2.3 times, respectively. Positive HIV status, rigors, pulse rate > 115bpm, deranged mentation, white cell count (WCC) > 18 (x109cells/L) and creatinine > 177 (μmol/L) were all risk factors for a positive BC. Conclusion: There was a low yield of positive BCs from the ED and using the SIRS criteria or the whole or components of the Shapiro score would improve the pre-test probability of a positive BC result in patients with suspected sepsis