Assessment of Factors Influencing the Positivity of Blood Culture by BacT/ALERT®3D Microbial Detection System: A Cross-sectional Observational Study

Abstract

Introduction: Bloodstream Infections (BSI) are defined as the presence of living microorganisms in the blood. It is a systemic condition that can result in life-threatening sepsis, thus leading to high morbidity and mortality. Blood cultures have become critically important. Positive blood culture results can help a clinician’s early diagnosis and start empirical antimicrobial at the correct time. Today many laboratories use modern, automated, continuous-monitoring blood culture systems for the detection of bacterial growth for blood culture. At our hospital, blood culture is done by using automated detection in BacT/Alert instrument (Biomerieux, France). Aim: To determine the effect of number of blood cultures and volume of blood on positivity rates, contamination rate in blood cultures, and rate of false-positive blood cultures. Materials and Methods: The present study was a cross-sectional observational study conducted from 1st May 2019 to 31st July 2019. Blood culture requests of all patients were included in the study. All blood culture bottles were processed as per standard laboratory protocols. The effect of number of blood cultures and amount of blood volume on positivity rate, contamination rate, and false-positive blood cultures were studied in detail. The patient’s details and microbiological result parameters were extracted from Laboratory Information System (LIS). All the data was analysed in Microsoft Excel 2010. Results: A total of 761 blood culture bottles were received at the Microbiology laboratory from 604 patients. Maximum (30%) blood cultures were received from 0-10 years of age group. A total of 31% (236/761) of blood cultures were positive. The true pathogen positivity rate was 41.1% and the contamination rate was 58.9%. Single (74.4%) blood culture requests were more than two (25.3%) or three (0.3%) blood cultures. True pathogens were isolated in 9% (41/449) of single blood cultures and in 18% (56/306) of two blood cultures. Overall, 42% of blood cultures had adequate volume and 58% of blood cultures had inadequate volume. However, the true pathogen positivity rate was 14% (61/444) from bottles with inadequate volume and 11% (36/317) from bottles with adequate volume. Out of 236 positive blood cultures, 139 (59%) were identified as contaminants. A total of 5/761 (0.7%) blood cultures were identified as false positive blood cultures. Conclusion: Based on the study findings, a step should be taken to discourage single blood culture and to encourage multiple blood cultures for the diagnosis and better patient care. Although, volume of blood is important, inadequate volume did not affect true pathogen positivity rate in present study. Contamination rate of blood cultures is a major concern and regular training of the concerned staff regarding strict asepsis should be implemented.

Keywords

• automated machine
• blood stream infections
• contaminants
• true positivity