Diagnostic accuracy of anti-HlyE and LPS antibodies in typhoid intestinal perforation in Niger

Typhoid intestinal perforation (TIP) is a late complication of Salmonella enterica serovar Typhi infection, and blood cultures, if available, are often negative at this stage, making etiologic confirmation challenging. In areas without access to blood culture diagnostics, TIP incidence can serve as a proxy for enteric fever burden. Antibodies against hemolysin E (HlyE) and S. Typhi lipopolysaccharide (LPS) are promising serologic markers for typhoid, but their diagnostic utility for TIP remains unclear. In this study, we assessed the diagnostic accuracy of anti-HlyE and anti-LPS IgG and IgA antibodies measured by kinetic enzyme immunoassay in children undergoing emergency laparotomy for acute abdomen in Niger. Dried blood spots (DBS) were collected pre-operatively (baseline) and within 30 days post-hospital discharge (convalescence). Patients classified intraoperatively as TIP (n = 341) or as confirmed non-typhoid-related alternative etiology (i.e., controls, n = 48) were included in this serologic analysis. The primary analyses were conducted in a longitudinal sub-cohort of 122 TIP cases and 33 controls in whom all four anti-HlyE and anti-LPS IgA and IgG responses were measured at baseline and at convalescence. Anti-HlyE IgA and anti-LPS IgA were additionally measured at baseline in the full analytic cohort. In the primary analysis, all antigen-antibody isotype combinations distinguished TIP cases from controls with high accuracy: anti-HlyE IgA (AUC 0.94), anti-HlyE IgG (AUC 0.94), anti-LPS IgA (AUC 0.96), and anti-LPS IgG (AUC 0.96). Anti-HlyE IgA and anti-LPS IgA performed similarly in the full cohort (AUC 0.93 and 0.93, respectively), supporting the representativeness of the sub-cohort. Anti-LPS IgG showed the best overall performance (99% sensitivity, 94% specificity), exceeding that of all other individual markers, and combining markers did not improve diagnostic accuracy. Diagnostic performance at convalescence was similar to or lower than that observed at presentation. Overall, anti-HlyE and anti-LPS antibodies showed high diagnostic accuracy for TIP at presentation, extending the potential utility of these serologic markers for supporting the diagnosis of typhoid-associated intestinal perforation and improving surveillance of severe typhoid disease when patients present with late-stage complications. Our findings show that serologic testing could improve case detection and burden estimation of enteric fever and its complications in resource-limited settings.