Rubella reinfection during pregnancy. A case of mistaken diagnosis of congenital rubella.

A case of subclinical rubella reinfection during pregnancy with serologic findings in the offspring initially led to an erroneous diagnosis of fetal infection. Laboratory diagnosis of congenital rubella infection, based on finding hemagglutination-inhibition (HI) activity in immunoglobulin M (IgM) fractions of newborn's serum after sucrose gradient fractionation, was questioned when apparent IgM-HI activity was to be probably due to nonspecific inhibitors, which resulted from bacterial action on the beta-lipoprotein in the serum. These findings emphasize some pitfalls encountered in arriving at a diagnosis based soley on serologic data. This case also illustrates the importance of keeping serum samples sterile when performing serologic tests.