Immune status of health care workers to measles virus: evaluation of protective titers in four measles IgG EIAs

Abstract

BackgroundFollowing the recognition of a measles case in a hospital in The Netherlands, health care workers (HCW) from the premises were screened by a commercial enzyme immunoassay (EIA) for measles IgG to identify persons at risk for measles. At least 10% of the HCW were tested measles IgG-negative. As this was considered an unusually high proportion, we hypothesized suboptimal sensitivity of EIAs, especially in medical personnel that had vaccine-induced immunity rather than antibodies resulting from natural infection. ObjectivesTo determine (vaccine-induced) measles immunity in HCW, using different EIAs compared to the plaque reduction neutralization (PRN) test, the best surrogate marker for vaccine efficacy and immune protection. Study designSera from HCW were tested for measles IgG antibodies in three commercial EIAs, in a bead-based multiplex immunoassay (MIA) and in the PRN test, and evaluated against age and vaccination history of the HCW. ResultsOf the 154 HCW, born between 1960 and 1995, 153 (99.4%) had protective levels of measles antibodies (PRN>120mIU/ml). The three EIAs failed to detect any measles IgG antibodies in approximately 10% of the HCW, while this percentage was approximately 3% for the MIA. Negative IgG results rose to 19% for individuals born between 1975 and 1985, pointing to an age group largely representing vaccinated persons from the first measles vaccination period in The Netherlands. ConclusionThe results show limitations in the usefulness of current EIA assays for determining protective measles antibodies in persons with a vaccination history.