In a neonate with "classic" symptoms of congenital cytomegalovirus (CMV) infection, which one of the following tests would be most useful in establishing a diagnosis?
A
CMV IgG titre on neonate's serum at bih
B
CMV IgG titre on mother's serum at bih of infant
C
CMV IgM titre on neonate's serum at bih and at 1 month of age