Microbial contamination risk in hematopoietic stem cell products: retrospective analysis of 1996–2016 data

An intermittent outbreak of Burkholderia cepacia contaminating hematopoietic stem cells resulting in infusate-related blood stream infections

Microbial contamination of hematopoietic stem cells (HSC), used for autologous and allogenic transplantations, is rare but could cause serious blood stream infection in transplanted patients. These infections occur immediately, or later following the formation of biofilm on the catheter lumen. The present study describes an intermittent B. cepacia HSC contamination associated with nosocomial bacteremia: from October 2011 to April 2015, 17 B. cepacia strains were isolated in HSC bags (n = 14) and blood cultures (n = 3) in patients hospitalized in the National Bone Marrow Transplant Center. Two epidemiologic investigations in the National Blood Transfusion Center, allowing the isolation of three strains in hygiene samples, and four interventions in this institution were done. To identify the source of this contamination, a molecular investigation was done on 23 B. cepacia strains isolated in our center from 2007 to 2015. PFGE analysis revealed five clusters. The major cluster included 18 strains isolated from HSC bags (n = 14), blood culture (n = 1), and water cans and bath (n = 3). The second cluster (B) including only two and the remaining clusters (C, D, and E) contained single strains isolated before the epidemic period. These findings confirmed that the origin of the outbreak was the contaminated water used in the water bath during the thawing step of HSC bags. Based on this result, new sterile water was used for every defrosting, but HSC bags contamination persisted. In May 2015, the water bath was replaced with a dry bath and no B. cepacia strain was isolated from that date to April 2020.

OUP accepted manuscript

Cord blood (CB) collected at birth has become a valuable stem cell source for hematopoietic stem cell transplantation (HSCT). However, the collection of umbilical cord blood always bears a risk of microbiological contamination, both in vaginal birth and in cesarean section. A total of 10 054 umbilical cord stem cell samples were successfully cryopreserved between 2010 and 2020, of which 783 (8%) samples were tested positive for bacterial contamination. Umbilical CB with a volume of less than 60 mL showed a bacterial contamination rate of 12%, and above 60 mL volume a rate of 6% was found demonstrating an inverse relationship between sample volume and contamination rate (correlation coefficient r = −0.9). The contamination rate was associated with the mode of delivery and showed a significantly higher contamination rate of 9.7% when compared with cesarean deliveries (1.4%). The 10-year period consistently shows an average contamination rate between 4% and 6% per year. It is conceivable that the inverse relationship between volume and contamination rate might be related to thinner veins although no scientific evidence has been provided so far. The lower contamination rate in cesarean sections appears to be related to the sterile operating setting. Overall, the rate of bacterial contamination varies and depends on the type of birth, the way of delivery, and probably the experience of the staff.

Effects of cryopreservation on gram-positive bacteria contaminants in umbilical cord blood

OBJECTIVE

To evaluate the effects of cryopreservation in post-thaw umbilical cord blood units for the survivability of Gram-positive bacteria strains.

BACKGROUND

Microbial screening is required for all cord blood units (CBUs). Four gram-positive contaminants were documented to survive cryopreservation poorly and isolation of other contaminants were reported.

METHODS

Forty-eight contaminated CBUs detected with either Staphylococcus epidermidis, Corynebacterium species, Peptostreptococcus or Streptococcus species before cryopreservation were used in this study. CBUs were processed, DMSO-infused and microbial screened before cryopreservation. Post-thaw microbial screening was achieved using 1 and 10 ml inoculants in BACTEC culture bottles. Positive bottles were subjected for microbial identification and results were compared with those from pre-freeze.

RESULTS

A higher rate of microbial contamination was found using the 10 ml inoculant. Screening of 11 CBUs did not detect any contaminants while 30 CBUs screened detected more than one unknown contaminants and majority of contaminants were identified to be gram-negative species.

CONCLUSION

A higher inoculation volume used at post-thaw for microbial screening improves contamination detection but leads to the loss of precious cord blood. Some contaminants did not survive cryopreservation or were not identified due to their low microbial levels. Contrasting contaminants found at post-thaw suggest the improvements made in detection and identification of contaminants over the years.

Improved harmonization of critical characterization assays across cell therapies

The field of cell therapy has blossomed, providing exciting new options for treating a variety of diseases. While few cell therapy products have US FDA approval, there are thousands of cell treatments at various stages of development, pointing to a potential revolutionary shift in patient care. The expanding number and nature of cellular therapies necessitate greater standardization. Several international organizations are collaborating to pursue some level of global standardization, especially concerning cell banking. However, less harmonization surrounds assays used for critical quality characterization including: identity, purity, safety and potency. Frequently, there is divergence regarding the terms describing the characterization assays across regulatory authorities and guidances. This review summarizes the critical quality assays currently used for different categories of cell therapies. Areas of harmonization and an absence of standardization are highlighted. We propose potential solutions to facilitate harmonization of critical quality characterization assays and the language used to describe them.