Prevalence, risk factors for infection and subtype distribution of the intestinal parasite Blastocystis sp. from a large-scale multi-center study in France

El Safadi et al. BMC Infectious Diseases (2016) 16:451 DOI 10.1186/s12879-016-1776-8 RESEARCH ARTICLE Open Access Prevalence, risk factors for infection and subtype distribution of the intestinal parasite Blastocystis sp. from a large-scale multi-center study in France Dima El Safadi1†, Amandine Cian1†, Céline Nourrisson2,3, Bruno Pereira4, Christelle Morelle5, Patrick Bastien5, Anne-Pauline Bellanger6, Françoise Botterel7, Ermanno Candolfi8, Guillaume Desoubeaux9, Laurence Lachaud10, Florent Morio11, Christelle Pomares12, Meja Rabodonirina13, Ivan Wawrzyniak3, Frédéric Delbac3, Nausicaa Gantois1, Gabriela Certad1, Laurence Delhaes1,14, Philippe Poirier2,3*† and Eric Viscogliosi1*† Abstract Background: Blastocystis sp. is the most common intestinal parasite of humans. Despite its potential public health impact, epidemiological data regarding the prevalence and molecular subtype distribution of Blastocystis sp. in Europe are rarely reported. Therefore, the first multi-center epidemiological survey performed in Europe was conducted in France to diagnose and subtype Blastocystis sp. and to identify risk factors for infection. Methods: Stool samples from 788 patients were collected either in summer or winter in 11 hospitals throughout France together with patient data. All stool samples were tested for the presence of Blastocystis sp. by quantitative PCR targeting the SSU rDNA gene. Positive samples were sequenced to determine the distribution of the subtypes in our cohort. Statistical analyses were performed to identify potential risk factors for infection. Results: Using quantitative PCR, the overall prevalence of Blastocystis sp. was shown to reach 18.1 %. The prevalence was significantly higher in summer (23.2 %) than in winter (13.7 %). Travellers or subjects infected with other enteric parasites were significantly more infected by Blastocystis sp. than non-travellers or subjects free of other enteric parasites, respectively. Different age-related epidemiological patterns were also highlighted from our data. The prevalence of Blastocystis sp. was not significantly higher in patients with digestive symptoms or diagnosed with chronic bowel diseases. Among symptomatic patients, Blastocystis sp. infection was significantly associated with abdominal pain. Gender, socioeconomic status, and immune status were not identified as potential risk factors associated with infection. Among a total of 141 subtyped isolates, subtype 3 was predominant (43.3 %), followed by subtype 1 and subtype 4 (20 %), subtype 2 (12.8 %), subtype 6 and subtype 7 (2.1 %). No association between ST and clinical symptoms was statistically evidenced. (Continued on next page) * Correspondence: ; † Equal contributors 2 Laboratoire de Parasitologie-Mycologie, CHU Gabriel-Montpied, Clermont-Ferrand, France 1 Université de Lille, CNRS, Inserm, CHU Lille, Institut Pasteur de Lille, U1019 – UMR 8204 – CIIL – Centre d’Infection et d’Immunité de Lille, 1 rue du Professeur Calmette, BP 24559019 Lille cedex, France Full list of author information is available at the end of the article © 2016 The Author(s). Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. El Safadi et al. BMC Infectious Diseases (2016) 16:451 Page 2 of 11 (Continued from previous page) Conclusions: A high prevalence of Blastocystis sp. infection was found in our French patient population. Seasonal impact on the prevalence of Blastocystis sp. was highlighted and recent travels and age were identified as main risk factors for infection. Most cases were caused by subtypes 1 to 4, with a predominance of subtype 3. Large variations in both prevalence and ST distribution between hospitals were also observed, suggesting distinct reservoirs and transmission sources of the parasite. Keywords: Blastocystis sp, Intestinal parasite, Molecular epidemiology, PCR, Subtyping, Risk factors for infection Abbreviations: HIV, Human immunodeficiency virus; IBD, Inflammatory bowel disease; IBS, Irritable bowel syndrome; OR, Odds-ratio; qPCR, Real-time quantitative PCR; ST, Subtype Background Blastocystis sp. is a common protozoan intestinal parasite with worldwide distribution that inhabits the digestive tract of humans and a large variety of animal hosts [1–3]. In numerous epidemiological surveys, this cosmopolitan enteric parasite was frequently identified as the most common unicellular eukaryote found in human fecal samples [1, 2, 4]. Indeed, its prevalence may reach 20 % in industrialized countries, including the European population [5] and 50 % in developing countries [6]. Recently, the prevalence of Blastocystis sp. was shown to be 100 % in a cohort of children living in a rural area in Senegal, highlighting the impact of blastocystosis mainly in developing countries with poor healthcare and hygiene [7]. In this regard, a higher prevalence of this parasite was found among European people with a history of recent travel to tropical countries [5]. At the morphological level, four major forms of Blastocystis sp. have been described, including the infective cyst which is able to survive for a long period in feces and environmental sources and is resilient to standard water chlorination, facilitating waterborne transmission of the parasite [1, 8]. Therefore, the fecal-oral route is considered the main mode of transmission of Blastocystis sp. through the consumption of food or water contaminated by cysts. Blastocystosis is usually diagnosed using direct-light microscopy of fecal smears or possibly short-term xenic in vitro culture of stool samples. However, these methods have a low diagnostic sensitivity compared with molecular tools, i.e. PCR assays, and could greatly underestimate the real prevalence of the parasite [9]. A remarkable genetic diversity has been revealed among Blastocystis sp. isolates from humans and other animals based on the comparison of small subunit (SSU) rRNA gene sequences. Consequently, seventeen lineages of socalled subtypes (ST1 to ST17) (arguably separate species) have been identified among mammalian and avian isolates [10], nine of which (ST1 to ST9) are found in humans with varying prevalence [2, 4]. The other STs (ST10-ST17) are exclusively found in animals [10]. Based on a recent review including all human samples subtyped thus far across various geographic regions worldwide [4], approximately 90 % of human isolates belonged to ST1 to ST4, with a predominance of ST3 (around 60 % of these isolates) (...truncated)