Prévalence des staphylocoques à coagulase négative dans les hémocultures au Centre Hospitalier Universitaire Ibn Rochd de Casablanca

INTRODUCTION: Blood cultures are the best diagnostic tool for the detection of bacteremia. However, false positive results may lead to confusion about antibiotic regimens, putting the lives of patients at risk. The main purpose of this study was to assess the prevalence of coagulase negative Staphylococci (CoNS) as well as of Corynebacterium spp and Bacillus spp in the bags of blood culture analyzed in the microbiology laboratory at the Ibn-Rochd University Hospital in Casablanca. This prevalence was evaluated according to various Hospital Departments over the year 2016. METHODS: We conducted a descriptive, retrospective study by analysing the computerized database of the Laboratory of bacteriology and virology at the Ibn-Rochd University Hospital in Casablanca over a 12-month period from 1(st) January to 31(st) December 2016. Our study focused on bacteria forming part of the commensal flora (coagulase negative Staphylococcus, Corynebacteria spp and Bacillus spp). The blood culture bags were incubated in the automated blood culture system (Bactec FX). The identification of the germs from a positive culture was performed according to the standard techniques of bacteriology and susceptibility testing was performed according to EUCAST 2015. We conducted an analysis of the computerized database of KALISIL system (Netika) version (2.2.10.) of the Microbiology Laboratory at the Ibn-Rochd University Hospital in Casablanca. RESULTS: Out of 7959 requests for blood cultures obtained from 5801 patients addressed to the laboratory of bacteriology, 2491 were positive, of which 848, reflecting a rate of 34% of positive bags or 10.6% of the whole of bags received over the year 2016, were positive for coagulase negative Staphylococcus, 56 bags of blood cultures, reflecting a rate of 2.2%, were positive for Corrynébacteruim SP, followed by 60 bags of blood cultures, reflecting a rate of 2.4%, which were positive for Bacillus sp. The frequency of isolation of coagulase negative Staphylococcus compared to other bacteria according to Clinical Departments showed a higher frequency in the Paediatric Department (47.2%) followed by the Medicine Department (44.1%). CONCLUSION: This study shows that coagulase negative Staphylococci are the organisms most frequently isolated from blood cultures. They are a non-negligible cause of nosocomial infections, but they are also the most common blood culture contaminants.