A Comparative Study to Determine the Recovery Rate of
Microorganisms of Bloodstream Infections: Two Versus
Three Blood Culture Specimens
Teerarat Shanthachol MD*,
Sumanee Nilgate Msc**, Chusana Suankratay MD, PhD*
Affiliation :
* Division of Infectious Diseases, Department of Medicine, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand
** National Streptococcal Reference Center in Thailand, Department of Microbiology, Faculty of Medicine,
Chulalongkorn University, Bangkok, Thailand
Objective : There has been a development of automated and continuous-monitoring blood culture systems that are more
sensitive than conventional systems for the detection of microorganisms. Whether two or three blood culture specimens
obtained during a 24-hour period using these automated systems achieving a higher recovery rate of microorganism remains
to be determined. The present study was aimed to compare the recovery rates of microorganism of blood-stream infections
(BSIs) using two and three blood culture specimens.
Material and Method: A prospective investigator-blinded study was carried out in patients who needed to have blood
cultures in medicine wards and intensive care units as well as an emergency room of King Chulalongkorn Memorial Hospital,
Bangkok, Thailand, between October 1, 2010 and March 31, 2011. Three blood culture specimens were obtained from each
patient during a 24-hour period. Each specimen was inoculated into an aerobic bottle of blood culture broth (TREK
Diagnostics, Cleveland, OH, US), and then incubated at 37°C for seven days.
Results : Of 568 patients, there were 116 (20.4%) unimicrobial episodes with three blood cultures obtained during a 24-hour
period. There were 70 (12.3%) and 46 (8.1%) episodes of true pathogen and contaminant, respectively. The recovery rates
of true pathogen were 75.7% (53 isolates), 87.1% (61 isolates), and 100% (70 isolates) with the first, second, and third
blood culture specimens, respectively (p < 0.05 between the recovery rate with the first two and the third blood culture
specimens). There were 25 (35.7%), 38 (58.6%) isolates, and four (5.7%) of Gram-positive, Gram-negative bacteria, and
fungi, respectively. Among 25 Gram-positive bacteria, Staphylococcus aureus was the most common isolate (10, 14.3%),
followed by Streptococcus pneumoniae (5, 7.1%) and Enterococcus faecalis, Enterococcus faecium, coagulase-negative
Staphylococcus (3, 10% each). Among 38 Gram-negative bacteria, Escherichia coli was the most common isolate (13, 18.6%),
followed by Pseudomonas aeruginosa (8, 11.4%), and Klebsiella pneumoniae (6, 8.6%). The sensitivity and specificity of
the recovery rate of microorganisms using two blood culture specimens were 85.7% and 92.3%, respectively. The sensitivity
and specificity of the recovery rate of microorganisms using three blood culture specimens were 100% and 90.8%, respectively.
Conclusion : To the best of the authors’ knowledge, the present study is the first prospective study to compare the recovery
rate of microorganisms of BSIs between the two and three blood culture specimens using the VersaTREK blood culture
system. Three blood culture specimens are required to achieve the recovery rate of more than 99%.
Keywords : Blood cultures, Cultures, automated blood cultures, Microorganisms, Recovery rate, Bloodsteam infections
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