Strongyloides stercoralis, the hidden worm. Epidemiological and clinical characteristics of 70 cases diagnosed in the North Metropolitan Area of Barcelona, Spain, 2003–2012

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Abstract
Background The nematode Strongyloides stercoralis has a very particular autoinfection life-cycle which leads to chronic infections remaining undetected for decades. However, hyperinfection can occur in patients receiving immunotherapy resulting in high mortality rates. The main objective of this study was to assess the results of a 10-year multicenter surveillance program performed in an area with dense immigration in Barcelona, Spain. Methods From January 2003 to December 2012, all individuals with Strongyloides stercoralis infection attending the four centers with diagnostic capability in the North Metropolitan area of Barcelona were recorded. Results The annual detection rate was 0.2 new diagnosed cases x10 000 inhabitants/year and 1 case x10 000 immigrants/year. Many patients were immigrants (63; 90.0%), asymptomatic (45; 64.3%) and with a high eosinophil count (63; 90.0%). Immunosuppression was present in 11 (15.7%) patients, among whom two (2.8%) cases of disseminated hyperinfection were recorded. Ivermectin was prescribed in 45 (76.3%) and albendazole in 14 (23.7%). Following treatment seven patients (11.9%) receiving albendazole presented relapse, that is, albendazole failed to clear the parasite in 50% of these drug-treated patients (p < 0.001). Conclusions During the study period, 90% of the cases of Strongyloides stercoralis diagnosed could be considered as imported by immigrants, most being asymptomatic and with eosinophilia. The infection is probably largely underestimated and population-based studies are needed to determine its true prevalence. Meanwhile, diagnosis must be based on active investigation of the helminth (serology and feces culture), especially in immunocompromised patients. The implementation of pre-immunosuppression protocols with the aim of identifying Strongyloides stercoralis is encouraged with empirical treatment with ivermectin being recommended in sites without diagnostic facilities.