Persistence of specific IgM after natural infection with rubella virus.

Levels of specific IgM antibody in thirteen cases of rubella were determined at intervals during the year after the illness. Persistence of IgM varied; in one patient it was no longer detectable at 23 days, but in two it was still detectable more than 10 months after the acute infection. Thus the mere finding of rubella-specific IgMin the blood does not indicate the timing of the acute episode any more accurately than some time within the previous 10-12 months.