A comparation of anti - LPS IgG as measured by the 2ME test or by ELISA in Human. Brucellosis

JORGE WALLACH; CARLOS A. FOSSATI; M. VICTORIA DELPINO; PABLO C. BALDI

España

Congreso; Brucellosis 2003 International Research Conference.; 2003

Abstract Among traditional serological tests for human brucellosis, the value of tube agglutination in the presence of 2-mercaptoethanol (2ME) has remained controversial. While the 0.005M 2-mercaptoethanol used in the test is assumed to destroy only IgM, the extent to which IgG is affected has never been addressed. We conducted a comparison between 2ME titers and levels of IgG to Brucella smooth lipopolysaccharide (LPS) measured by ELISA in 158 serum samples referred to our laboratory. These samples were from people with confirmed recent or past brucellosis (patients), individuals with positive slide agglutination in blood bank or pre-laboral tests, and persons with symptoms compatible with brucellosis that were referred for serological confirmation of the disease (suspected brucellosis). Anti-LPS IgG levels were expressed as a positivity index (PI), calculated as the optical density yielded by each sample divided by the cut-off of the assay. Anti-LPS IgG was considered negative when the PI was £ 1, weakly positive for PI between 1 and 2, and strongly positive when the PI was higher than 2. Sixty-four samples were negative by 2ME, 20 were positive with a titer of 25, 28 yielded a titer of 50, and 46 had a titer of 100 or higher. Anti-LPS IgG was strongly positive for 52 (81%), 19 (95%), 26 (93%), and 46 (100%) of these samples, respectively. A separate analysis was performed for the samples that showed the most discordant results (negative or 25 by 2ME, strongly positive by ELISA). The standard tube agglutination (STA) had yielded significant titers (³ 100) in 13 (25%) of the 52 samples with negative 2ME and in 8 (42%) of the 19 samples with a 2ME titer of 25. Among the 52 subjects with negative 2ME and high levels of IgG, 32 had documented recent or past brucellosis, including 25 (48%) with current clinical manifestation; other 18 individuals had compatible symptoms but lacked bacteriological confirmation of the disease. Among subjects with a 2ME titer of 25, 14 (74%) had documented brucellosis with current clinical manifestation. These results suggest that a significant proportion of patients with active brucellosis are missed by the 2ME test, but can be correctly diagnosed if anti-LPS IgG is measured by ELISA.