Community screening campaign for Strongyloides stercoralis among Latin American immigrants in Spain

Strongyloides stercoralis is a soil-transmitted nematode that is highly prevalent in Latin America, sub-Saharan Africa and South East Asia where it is estimated that, ∼100 million people are infected by S. stercoralis. Strongyloides stercoralis has several peculiarities: it has the capacity to reproduce within a human host producing endogenous autoinfection, which can cause long persistent infections; it can cause systemic infection, mainly in immunosuppressed individuals, generating a hyperinfection syndrome that can be potentially fatal [].

Immigrants coming from countries where S. stercoralis is endemic have been described as having high prevalence rates of chronic S. stercoralis infections that in most cases show up as asymptomatic and that can persist for many years after arriving at the host country []. Therefore, screening among those immigrants at risk could be an effective measure.

We performed two community screening campaigns for Chagas disease and strongyloidiasis in 2016 in Spain: one in Alicante organized by the University Hospital of Alicante in collaboration with Mundo Sano Foundation (MSF) and another in Madrid by the National Referral Unit for Tropical Diseases of the Ramón y Cajal University Hospital in collaboration with MSF (http://www.mundosano.org/) and the non-governmental organization ‘Salud entre Culturas’ (http://www.saludentreculturas.es). Salud entre Culturas and MSF were in charge of promoting the event within the Latin American community a few weeks before the event with the help of Bolivian community health workers specialized in Chagas disease at non-governmental organizations and migrants' associations; by distributing printed material and placement of posters; through social networks and by radio and newspapers aimed at the Latin American population. The community screening campaign was approved by the Ethics Committee of the Ramon y Cajal Hospital and participants signed a written informed consent (CEIC 138/16). Diagnosis of strongyloidiasis was carried out at the National Microbiology Centre ISCIII using a Strongyloides IgG IVD-ELISA kit (DRG Instruments GmbH, Marburg, Germany) and the ELISA test was considered positive if the index (Optical Density of sample/Cut Off) was >1.1. The result was considered indeterminate if the index was between 1.0 and 1.1.

A total of 789 individuals were screened for S. stercoralis: 129 in Alicante and 660 in Madrid. Thirty-seven who were children born in Spain, were removed from the statistical analysis, so a total of 752 participants were analysed, reporting a 10.1% (76/752) prevalence of S. stercoralis infection. Characteristics of the screening campaign and the comparison between those with positive and negative S. stercoralis serology are displayed in Table S1 (see Supplementary Material). Those participants with an indeterminate result on the serology (n = 3) were not included in the comparison.

Ideally, the criteria that a disease should fulfil to justify its screening should be the following.

• •
  It must be a prevalent disease. Studies performed among immigrants and refugees using serological enzyme immuno-assays have reported prevalence rates of S. stercoralis between 9% and 77% among those coming from South East Asia and Africa and prevalence between 5% and 26.8% among those coming from Latin America [

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  ]. Prevalence observed in these screening campaigns among Latin American immigrants has been as high as a 10%.
• •
  It can persist asymptomatically. Strongyloides stercoralis is a parasitic infection that can persist for years or decades, asymptomatic in most infected individuals [

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  ]. In our screening campaigns, diagnosis was made a long time after arriving in Spain (mean time of 11 years).
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  It must have a high-sensitivity diagnosis test. Diagnosis for these screening campaigns was performed by serology, which is the most sensitive diagnostic test. It has been estimated that enzyme immunoassays for S. stercoralis have 100% sensitivity and 88% specificity. Another diagnosis option is the stool larvae examination. However, testing of three samples can result in <60% sensitivity [

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  The diagnosis must be followed by a therapeutic option. In this campaign, all with a positive or indeterminate result for S. stercoralis were given an appointment at the National Referral Unit for Tropical Diseases of the Ramón y Cajal University Hospital and the University Hospital of Alicante for treatment and follow up. Ivermectine is currently the first drug chosen for acute, chronic and hyper-infections or disseminated strongyloidiasis [

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  ]. A 2-day course of ivermectin (200 μg/Kg/day taken orally once a day and repeat 10 days after) was administered to those participants of the screening campaign with a positive result for S. stercoralis.
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  Early diagnosis and treatment should improve the prognosis of the disease. The objective of the treatment of S. stercoralis is to eradicate the infection, and hence reduce morbidity and mortality, preventing hyperinfection among immunosuppressed individuals (those receiving treatment with corticosteroids, those with human immunodeficiency virus infection, organ transplantation, human T-lymphotropic virus infection, alcoholism or malnutrition) [

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  ]. Screening and treating S. stercoralis among immigrants may also have a public health impact. Cases of S. stercoralis infection in solid organ transplant recipients where transmission was through an infected donor have been described [

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  ]. In Spain, data from the National Organization of Transplantation reported that in 2006, 9.25% of organ donors were born abroad (http://www.ont.es/prensa/NotasDePrensa/Porcentaje%20donacion%20inmigrante.pdf).

This paper reflects how a community screening campaign can be an effective measure for S. stercoralis diagnosis among asymptomatic immigrants coming from countries of high endemicity in Latin America such as Bolivia. This may be because of the intense and targeted recruitment campaign performed with the help of the community health workers, because the screening was performed in a non-clinical setting, avoiding administrative barriers, and because the screening was performed on a Sunday (outside working hours), which allowed many migrants with a precarious and irregular employment status to assist.