2.3 Infectivity assay (TCID50)
Samples that potentially contained infectious virus were titrated by
tissue culture infectious dose 50% (TCID50) assay, that
is, eightfold replicates of serial half-log sample dilutions were
incubated with cells for 5-7 days and CPE was assessed microscopically.
Virus concentrations were calculated according to the Poisson
distribution and expressed as viral load (log10[TCID50]).