RSV A2, BT2a P.3 and BT2a P.14 multistep growth curves. PBEC monolayers from 3 individual donors were infected with RSV A2, BT2a passage 3 and BT2a passage 14 at MOI 0.1 to determine if multiple passages of a clinical isolate in HEp-2 cells influence growth kinetics of the clinical isolates in PBECs. Cells were scraped into the medium and harvested every 24 h post infection. Virus growth kinetics were determined by titrating virus in each sample. The data are presented as mean ± S.E. log10 TCID50/ml.