Prior to the water filtration, a test was performed to ensure that cell
culture medium (EMEM) containing 2% FBS was able to reproducibly
release virus particles from the electropositive 1 MDS filters. Water
samples were spiked with ISA virus with a TCID50 concentration in a
range of 5.3 × 104 virus mL−1 to 6.6 × 106 virus mL−1 and the virus
recovery after filtration was on average 36.5%. The reading of the
TCID50 dilution series was done by using IFAT (Falk et al., 1998).