Clinical manifestations of cytomegalovirus (CMV) infection may not be readily apparent at bih. Thus, in a newborn infant with a 1:32 titer of CMV, it is necessary to determine whether the antibodies were passed transplacentally from the mother (these antibodies would be IgG) or produced by the fetus in response to an in utero infection (lgM). A newborn infant who is infected excretes large numbers of virus paicles in the urine and, therefore, places other neonates at risk for contraction CMV disease.