Strongyloidiasis Beyond the Tropics: Updated Epidemiological Evidence from a Historically Endemic Region in Spain

Strongyloidiasis is traditionally regarded as a tropical disease; however, in the Valencian Community (Spain), it has historically been linked to localized endemic foci considered of declining relevance. This was a multicenter regional case series study across three hospitals including patients ≥16 years with strongyloidiasis defined by positive serology and/or parasitological confirmation diagnosed from 2015 to 2024. A total of 301 patients were included (median age 53 years (quartile 1–quartile 3, 40–72); 135 (44.9%) female). Most cases were autochthonous (176/299, 58.9%), while 123/299 (41.1%) occurred in migrants, predominantly from Latin America. Symptoms were present in 165/296 (55.7%), most frequently cutaneous (68/296, 23.0%) and gastrointestinal (62/296, 20.9%). Eosinophilia (>500 cells/µL) was observed in 144/298 (48.3%) and severe infection (hyperinfection syndrome) in 7/294 (2.4%). Annual diagnoses increased over time, with a significant temporal trend by case origin (p < 0.001), reflecting an increasing contribution of imported infections, whereas trends by sex (p = 0.068) and immune status (p = 0.926) were not significant. Stool-based methods demonstrated a low diagnostic yield (microscopy 7/157, 4.5%; culture 21/136, 15.4%; rtPCR 2/27, 7.4%). These findings document the sustained detection of cases classified as autochthonous beyond historically recognized foci and an increasing proportion of imported diagnoses in a temperate European setting.