Diagnostic performance of a Strongyloides IgG4 Rapid Test in detecting human Strongyloides stercoralis infection

Soil-transmitted helminths (STH) affect more than 1 billion people worldwide. Due to the morbidity in children caused by the accumulation of infections with these parasites, the World Health Organization (WHO) developed deworming programs to reduce worm burden, providing guidelines for Ascaris lumbricoides, Trichuris trichiura, and hookworms, since they are diagnosed and treated using the same tools. Recently, the WHO has provided guidelines for Strongyloides stercoralis, given it requires specific tools for diagnosis and treatment, with the goal to reduce prevalence and encourage the study of new diagnostic algorithms for deworming campaigns in areas where all STHs are present. Herein, we present an evaluation of the SsRapid, a prototype serological test developed to detect S. stercoralis IgG4.

A cross-sectional study was conducted in indigenous communities of Puerto Iguazú (Misiones) during 2023, an endemic area for STH in Argentina. Stool samples were analyzed using coprological methods (sedimentation and Baermann) for helminth parasite detection. Serum samples were analyzed for S. stercoralis-specific antibodies using a standardized in-house NIE-ELISA and the SsRapid test. Diagnostic performance was assessed through two analytical frameworks: (i) conventional analysis using coprological methods as a reference standard and (ii) latent class analysis (LAC) to account for the imperfect nature of all diagnostic tests and estimate true sensitivity and specificity without assuming a gold standard.

A total of 327 stools and 226 serum samples were collected and processed. The overall copro-parasitological prevalence of all species of STH, including S. stercoralis, was 69.7%. Hookworm was the most prevalent STH detected (59.0%), followed by S. stercoralis (25.7%). The seroprevalence of S. stercoralis using SsRapid and in-house NIE-ELISA was 51.3% (95% CI 44.8-57.8) and 39.4% (95% CI 33.1-45.8), respectively; a statistically significant difference (P = 0.0049) was observed between the assays. Compared to coprological methods, the diagnostic sensitivities of the SsRapid and in-house NIE-ELISA were 86.8% [95% CI 74.6-94.5] and 69.8% [95% CI 55.6-81.6], respectively. LAC, which does not assume a perfect gold standard, estimated a higher true prevalence of 30.7% and identified SsRapid as the most sensitive test (94.3%) and copro-parasitological methods as the most specific (95.9%). The model demonstrated adequate class separation (entropy = 0.68).

Both conventional analysis and latent class modeling consistently demonstrated the superior sensitivity of SsRapid compared to in-house NIE-ELISA and copro-parasitological techniques. The LAC further strengthened these findings by providing unbiased estimates that confirmed SsRapid as the most sensitive test (94.3%) and revealed a higher true disease burden (30.7%) than apparent by coprological methods alone. Therefore, SsRapid is a promising field diagnostic tool for detecting S. stercoralis in deworming programs.