Avidity of IgG for rubella: an evaluation of the need for implementation at the Materno-Infantil Presidente Vargas Hospital in Porto Alegre, Rio Grande do Sul, Brazil

Rubella serum assays performed in the laboratory of the Materno-Infantil Presidente Vargas Hospital (HMIPV) from 1998 to 2002 were reviewed to determine if IgG avidity assays should be implemented. IgG was determined using the Enzyme Linked Fluorescent Assay, ELFA, VIDAS system, bioMerieux or the Microparticle Enzyme Immunoassay, MEIA, Axsym system, Abbott, and IgM was determined using the ELFA, VIDAS system, bioMerieux, a capture format assay. Specific IgG was assayed in 2,863 samples, with positive results for 84% of the patients, for the most part with high levels of antibodies. IgM was assayed in 2,851 samples, being positive in 14 (0.49%) and inconclusive in 25 (0.88%). Serology for toxoplasmosis was also positive or inconclusive in 5 patients. After a cost-effectiveness analysis, it was decided not to implement avidity assays, considering that the HMIPV is a public institution, with limited funding. Difficulties concerning the integration of the Clinical Pathology Service with the Clinical Staff of the institution were also considered.