Microbiological contamination of allogeneic stem cell products

Abstract

Introduction: Regulated by German legal authorities quality control of stem cell products includes product volume, number and viability of CD34+ (PBSC products) or nucleated cells (bone marrow products), number of CD3+ cells (PBSC products), hematocrit and sterility testing. Material and Method: We performed a retrospective analysis of microbiological contamination of allogeneic stem cell products. Over the last seven years we performed 1051 peripheral blood stem cell collections and 300 bone marrow collections. For all products sterility testing was performed using BactAlert device. If result of screening was positive, differentiation of germs was done in a specialized microbiological laboratory. Results: 96 out of 1051 peripheral stem cell products (9,1%) and 1 out of 300 bone marrow products (0,3%) showed positive signal in BactAlert screening test. 14 out of 1051 peripheral stem cell products (1,3%) and 1 out of 300 bone marrow products (0,3%) were contaminated with bacteria. Fungi were not detected. In PBSC products Staphylococcus species, Propionibacteria and Streptococcus species were detected. In BM product Staphylococcus capitis was found. Discussion: Because of higher cell count rate of false positive BactAlert results is nearly 10% in PBSC products. But only 1,3% of all products is really contaminated with bacteria. All detected germs belong to normal skin flora and went into apheresis product via vein puncture. Even if skin disinfection is done properly sometimes not all bacteria are devitalized. You could expect same constellation in bone marrow collection procedure. But surprisingly we found lower contamination rate in BM product. Possibly complete shaving of puncture area contributes to this finding. Nevertheless allogeneic stem cell products extremely seldom cause dangerous bacteremia in patients, because detected bacteria respond to antibiotics, patient are given during cytopenia.