IMMUNOGLOBULIN-M ANTIBODY-RESPONSE TO MEASLES-VIRUS FOLLOWING NATURALVIRUS-INFECTION, PRIMARY VACCINATION, AND REEXPOSURE TO THE VIRUS

Evaluation of the measles virus ELISA kit (Merck) to detect specific I gM as an indicator of primary measles antibody response was carried ou t. A modification of the manufacturer's cutoff value interpretation wa s introduced to allow for equivocal results in addition to positive an d negative ones. With this modification, the test assayed gave an over all reproducibility of 96.16%. The IgM seropositivity rate for seroneu tralization-confirmed measles cases was 100% far naturally infected me asles subjects and 90% for primary measles vaccinated subjects. Indivi duals with positive neutralizing antimeasles antibodies in close conta ct with a confirmed measles case gave the following measles IgM ELISA results: 54.54% negative, 9.09% positive, and 36.36% equivocal, showin g a booster with IgM antibody response on reexposure to the virus. Pos itive subjects with neutralizing antimeasles antibodies without recent contact with a measles case gave negative IgM results. IgM seropositi vity was strongly associated with IgG seroconversion and clinical meas les (p < 0.0001). The technique assayed performed adequately for the c onfirmation of both measles natural infection and primary vaccination and for the differentiation of primary and secondary antibody response , taking into account the modification in the cutoff value interpretat ion introduced and providing that the serum samples are obtained betwe en days 5 and 30 after onset of rash.