ObjectiveTo evaluate bacteria contamination during collection,processing and storage of cord blood to gain insight into contamination mechanism and direct prevention.MethodsFresh cord blood was separated by hydroxyethyl starch (HES) to harvest nucleated cells.The bacteria contamination was tested by culturing 10 ml plasma-red cells with BacT/ALERT 3D-480 automatic blood culture system.Total 87 positive samples were further identified for bacteria species.Ninety six cord blood nucleated cells concentrate with bacteria positive stored in liquid nitrogen(LN2) for 6-7 years were thawed at 37 C and re-cultured for bacteria analysis.ResultsWe collected 19 062 umbilical cord blood.Among them,336 was bacteria positive ( contamination rate 1.8 ％ ).Eighty-seven positive samples were further investigated with facultative bacteria 58 (66.7 ％ ),aerobic 38(43.7％ ) and anaerobic 17( 19.5％ ),Gram- negative accounted for 68％ while positive 32％.The most frequent bacteria were Escherichia coli ( 25.3％ ),Streptacoccus intermediate ( 14.9％ ) and Chromobacteria violaceum(9.2％ ).Ninety-six nucleated cells concentrate with bacteria positive were cryopreserved at liquid nitrogen for researching.Of them,83 samples( 86％ ) showed positive of bacteria culture after deep-low temperature storage for 6-7 years.ConclusionsBacteria contamination rate of the cord blood collection,processing and storage in 2000 ～ 2007 was 1.8％.Stored in liquid nitrogen for 6-7 years,the viability of bacteria was 86％.The aseptic procedures of cord blood collection in delivery room should be intensified.The bacteria re-culture following thawing of cord blood cells is necessary before clinical transfusion.