A Paired-Marker Framework for Interpreting Anti-Ascaris lumbricoides IgG Serology and Copromicroscopy: A Cross-Sectional Study in Almaty and the Almaty Region, Kazakhstan
Background. Stool microscopy and anti-Ascaris IgG serology assess different, but related biological domains. Joint interpretation can identify immunological exposure and intestinal egg shedding without assuming one or both markers are a measure of current infection independently. Objective. To develop a four-pattern paired-marker framework for anti-A. lumbricoides IgG and copromicroscopy results from adults in Kazakhstan and to assess the qualitative analytical concordance of two IgG enzyme-linked immunosorbent assays (ELISAs). Methods. The cross-sectional field study involved 1000 adult volunteers from Almaty and the region providing matched serum and stool samples. Sera were tested by MVA Group indirect anti-Ascaris IgG ELISA, and stool samples were examined by the Kato–Katz and Fülleborn methods. The binary outcome was classified into four pair patterns. All sera were further tested with a commercial ELISA (DRG), and qualitative concordance was calculated. Results. Anti-Ascaris IgG was found in 331 of the 1000 subjects (33.1%; 95% CI, 30.3–36.1%), while A. lumbricoides eggs were detected in 240 subjects (24.0%; 95% CI, 21.5–26.7%). The paired patterns were IgG-positive/egg-positive in 185 participants (18.5%), IgG-positive/egg-negative in 146 (14.6%), IgG-negative/egg-positive in 55 (5.5%), and IgG-negative/egg-negative in 614 (61.4%). IgG positivity was detected in 77.1% of subjects with detected eggs and 19.2% of subjects without detected eggs (odds ratio, 14.15; 95% CI, 9.96–20.09; p < 0.001). The MVA Group and DRG ELISAs agreed for 990 of 1000 specimens (99.0%; 95% CI, 98.2–99.5%), with positive and negative agreements of 98.2% and 99.4%, respectively (κ = 0.98). Conclusions. Serology and copromicroscopy showed a high association, but they are not interchangeable. The paired-marker paradigm clarified concordant and discordant patterns while retaining IgG as a marker of past or ongoing immune exposure and stool eggs as markers of shedding at the time of sampling. High inter-assay agreement suggests analytical consistency within this serum panel, but does not imply diagnostic accuracy for active ascariasis.