Background and objectives: Microbiological follow-up is part of quality control of peripheral blood stem cell (PBSC) manipulation.
Design and methods: We prospectively studied microbiological cultures performed in 865 consecutive untreated autologous PBSC harvests from 348 patients. Our aim was to know the rate of microbiological contamination, the optimum moment to evaluate the sample and the clinical significance of the positive findings.
Results: Fifty-nine of the 852 samples (6.9%) yielded a positive culture after PBSC collection (sample 1) and 62 samples also yielded positive results before cryopreservation (7.2%) (sample 2). At the time of the analysis, a total of 520 aphereses had been infused and the number of positive cultures after thawing (sample 3) and after washing (sample 4; 82 aphereses) was 5.4% and 2.3%, respectively. Most of the positive cultures were due to coagulase-negative staphylococci (48 isolates). After thawing 15 coagulase-negative staphylococci and 2 enterococci isolates were recovered. Comparison between samples using a marginal homogeneity test showed no differences in the rate of contamination observed at the different sampling points.
Interpretation and conclusions: Positive microbiological findings in collected PBSC are not due to contamination within the laboratory. Cryopreservation using DMSO does not eradicate bacteria and manipulation does not seem to affect results. To simplify the procedure it would be possible to eliminate the microbiological controls performed immediately before cryopreservation.