Mechanism of cross-contamination of blood culture bottles in outbreaks of pseudobacteremia associated with nonsterile blood collection tubes.

Several studies have identified nonsterile blood collection tubes as the reservoir for contaminating microorganisms in outbreaks of pseudobacteremia. Microorganisms are thought to be transferred from the nonsterile tubes to the blood culture tubes when blood is drawn for cultures, but the validity of this hypothesis has not previously been tested. We recently investigated an outbreak of Ewingella americana pseudobacteremia in which an epidemiological association was found between pseudobacteremia and the practice of drawing blood for culturing at the same time that blood for coagulation studies is drawn. The nonsterile coagulation tubes, prepared in the hospital, were contaminated with E. americana. We studied three different procedures that personnel reported using to inoculate blood culture tubes after dispensing blood into the coagulation tubes. Although the failure to change or remove the needle before inoculating the blood culture tubes resulted in the highest percentage of cross-contamination, we found that all the techniques we simulated carried some risk of cross-contamination when coagulation tubes were filled first.