Comparison of True Positivity and Contamination of Blood Cultures: A Cross sectional Study

Abstract

Background: Blood cultures are done for the detection of bacteremia. Identification of the antibiotic sensitivity of major blood borne pathogens is important for selecting an effective antimicrobial drug and provide better patient care management. Objectives: To compare the proportions of blood culture positivity, causative bacterial pathogens, antibiotic sensitivity pattern and common contaminants of positive blood cultures between the Emergency Treatment Unit (ETU) and general wards (GW) in Teaching Hospital Karapitiya (THK) Methods: A cross-sectional retrospective study was carried out from January to March 2022. All the consecutive patients admitted to the ETU and GW in THK were included and analysed using SPSS. Chi-squared test was used to test the associations between variables. Results: A total of 353 blood culture reports from ETU and 1271 from GW were analysed.The proportions of true positivity of blood cultures in ETU and GW were 24.1% (n=85) and 9.4% (n=119), respectively. E. coli was the most frequently isolated pathogen in ETU (36.5%) and GW (21.3%). E.coli and Klebsiella spp. were sensitive for amikacin (94.6%, 100%), imipenum (91.7%, 93.3%), gentamicin (77.7%-85%). Acinetobacter spp. showed higher resistant rates. Susceptibility of Pseudomonas spp. was 83.3% to gentamicin. Among Staphylococcus aureus, proportion of MSSA and MRSA were 10.3% (n=21) and 10.3% (n=21), respectively. Group B streptococci and Streptococcus pneumoniae were susceptible to penicillin (100%).The proportion of contamination was significantly higher in ETU (12.5%) compared to GW (7.25%) (p<0.001). The commonest contaminant was Coagulase negative Staphylococcus spp. Commensal organisms were considered as contaminants except central-line associated bloodstream infections and repeated culture positivity with same organism with same antibiotic sensitivity pattern. Conclusions: The blood cultures from ETU showed higher values for both true positivity and blood culture contamination compared to GW. Gram-negative bacteria were the commonest isolated pathogen.These findings will assist healthcare professionals to take measures to reduce blood culture contamination and to utilize the resources effectively. Keywords: Antibiotic sensitivity pattern, Blood borne pathogens, Blood culture contamination,