The Accuracy of Serologic Diagnosis of Helicobacter pylori Infection in School‐aged Children of Mixed Ethnicity

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Abstract
The present study evaluated two non‐invasive diagnostic methods for H. pylori infection in children, i.e. an in‐house ELISA using sonicated Campylobacter jejuni antigen for absorption of cross‐reacting antibodies and an immunoblot kit (Helico Blot 2.0, Genelabs, Singapore). 13C ‐Urea breath test (13C‐UBT) was used as reference method. Sera and questionnaires were collected from 695/858 (81%) Swedish school children with mixed ethnic backgrounds within a cross‐sectional, community‐based study. Of 133 children with an ELISA OD value of ≥ 0.1, all were screened with immunoblot and 107 made a 13C‐UBT. The negative controls were 34/37 children from three school classes with an ELISA OD value of < 0.1 and volunteering for a 13C‐UBT. An adjusted cut‐off level for the ELISA of OD value 0.22 resulted in a sensitivity of 97.8%, a specificity of 95.8% and a concordance index of 97.2%. The Helico Blot 2.0 had a sensitivity of 97.8%, a specificity of 93.8% and a concordance index of 96.5%. The best concordance was seen for the 26.5 kDa (98.6%), 30 kDa (95.7%) and 19.5 kDa (91.5%) antigens. The corresponding concordance index for CagA was 78%, for VacA 73.8% and for the 35kDa antigen 68.8%. A significant difference in the distribution of the 19.5 and 26.5 kDa bands but not of CagA/VacA was noted by ethnic background. With an adjusted cut‐off level for the enzyme‐linked immunosorbent assay (ELISA), both non‐invasive methods were found to have an adequate performance in a pediatric population. The differences in antibody response patterns by ethnic background represent a caveat in the interpretation of serological studies.