Toxoplasma gondii IgG seroprevalence in Qatar and the impact of assay variability on epidemiological estimates.

Toxoplasma gondii is a globally prevalent protozoan parasite of major public health importance. Serological detection of IgG antibodies is widely used to estimate population-level exposure; however, reported seroprevalence varies substantially across studies, in part due to differences in assay design and analytical performance. A total of 2002 archived serum samples from the Primary Health Care Corporation (PHCC) were analysed using the Mindray chemiluminescent immunoassay (CLIA) to estimate national T. gondii IgG seroprevalence in Qatar. A randomly selected subset of 400 samples was additionally tested using Architect chemiluminescent microparticle immunoassays (CMIA) system and NovaLisa ELISA. In the absence of a biological reference standard, results were interpreted strictly as measures of agreement rather than diagnostic accuracy. Based on Mindray CLIA testing, the estimated T. gondii IgG seroprevalence was 32.5%. Within the comparative subset, Mindray classified 35.9% of samples as IgG-positive, compared with 26.9% by NovaLisa ELISA and 24.5% by Architect CMIA, corresponding to a 34-47% higher IgG detection rate. Agreement between NovaLisa and Architect was near-perfect (κ = 0.87; OPA = 95.1%), while agreement between Mindray and the other assays was moderate (κ ≈ 0.51; OPA ≈ 78%). NPA values were high (77.7-100%), whereas lower PPA values (55.6-93.5%) indicated discordance driven mainly by IgG-positive classification. Seropositivity across any assay reached 42.8%, while only 19.1% of samples were positive across all platforms. T. gondii IgG seroprevalence in Qatar is strongly influenced by diagnostic platform selection, highlighting the need for local assay validation and cautious cross-platform interpretation.