Background: The purpose of this study was to investigate the persistence of viable Ehrlichia chaffeensis in ADSOL-treated RBCs stored at 4 to 6 degrees C.
Study design and methods: The continuous monocytic cell lines THP-1 and DH82 were infected with E. chaffeensis (St. Vincent isolate). Packed RBC units were inoculated in separate experiments with E. chaffeensis-infected cells as final concentrations of 8.02 x 10(4) (DH82) and 1.43 x 10(4) (THP-1) infected cells per mL. Aliquots were stored at 4 to 6 degrees C for 1 to 42 days. At selected intervals, nucleated cells from the RBC aliquots were obtained by using a ficoll-isopaque separation procedure. Uninfected DH82 cell cultures were inoculated with the harvested nucleated cells or supernatant. The cell cultures were evaluated for infection by weekly examination of Wright's (Diff-Quik) stained cytocentrifuged slides. PCR amplification was also used to test the harvested nucleated cells or supernatant for the presence of E. chaffeensis DNA.
Results: In both types of infected cell lines, E. chaffeensis was reisolated in DH82 cells for as long as 11 days from the cellular fraction and for up to 5 days from the supernatant fraction. PCR results were positive throughout the 42-day testing period.
Conclusion: Cell-associated E. chaffeensis remains viable in ADSOL-treated RBCs stored at 4 to 6 degrees C for at least 11 days. These data suggest that transfusion-acquired infection is possible. Successful reisolation was achieved from the supernatant fraction, which suggests that RBC products treated with a WBC-reduction procedure may still present a risk for transfusion transmission. No correlation between PCR positivity and viability of bacteria was noted.