Evaluation of Brucella IgM and IgG ELISA Responses in Relation to Blood Culture Positivity in Pediatric Brucellosis

Abstract

Background Class-specific Brucella IgM and IgG enzyme-linked immunosorbent assay (ELISA) responses according to blood culture status are incompletely characterized in children with confirmed brucellosis. We compared IgM and IgG ELISA findings according to contemporaneous blood culture status among children already classified as having confirmed acute brucellosis; diagnostic accuracy was not assessed. Methods This retrospective, single-center, cross-sectional observational study included 94 children aged 18 years or younger. Rose Bengal testing, standard tube agglutination testing (STAT), Brucella IgM and IgG ELISA, and blood culture were obtained at the same presentation. Serologic findings were compared by culture status, and factors associated with culture positivity were explored using multivariable logistic regression. Results Blood cultures yielded Brucella melitensis in 49/94 children (52.1%). IgM ELISA was positive in 93/94 (98.9%). IgG ELISA was positive in 70/94 (74.5%), equivocal in 4/94 (4.3%), and negative in 20/94 (21.3%). IgM values did not differ significantly between culture-positive and culture-negative groups (41.2 ± 15.8 vs 36.2 ± 12.6 NTU; p=0.096). IgG values were lower in culture-positive children (median 18.5 vs 21.0 NTU; Mann–Whitney U=789; p=0.018; rank-biserial correlation=0.284). After excluding equivocal results, IgG negativity was more frequent in culture-positive than culture-negative children (14/47 [29.8%] vs 6/43 [14.0%]), but not significantly (Fisher exact p=0.082). Fever with arthralgia, elevated C-reactive protein, and elevated aspartate aminotransferase remained associated with culture positivity in the exploratory model. Conclusion Among children with confirmed acute brucellosis, IgM ELISA was positive in nearly all patients, while continuous IgG values were lower in culture-positive children. These findings describe associations with contemporaneous culture status and should not be interpreted as antibody kinetics or diagnostic-performance estimates. ELISA values should not be used alone to predict blood culture positivity or determine whether blood culture should be obtained.