Detection of risk factors associated to Blastocystis hominis infection

Introduction: Blastocystis hominis is the most common intestinal parasite isolated in humans. However, a lot of controversies still surround it. Even it has a worldwide distribution, with a higher prevalence in developing countries, its burden is still under-estimated. Nowadays, interest concerning it is increasing due to its potential role as a human pathogen. The aim of the study is to detect the risk factors associated to Blastocystis hominis infection. Materials and Methods: a case-control retrospective study was carried out at Vall d'Hebron University Hospital, a reference Hospital that receives all microbiological tests performed in Barcelona at primary care level. Eligible patients were those adults in whom with three consecutive stool samples that had been examined for parasitic infection diagnosis during 2017. Blagg's technique (merthiolate-iodine-formaldehyde concentration) was used to microscopically examine Blastocystis sp. Medical record review and telephonic interviews were carried out in order to gather clinical and epidemiological information. Results. Overall, 4174 patients were eligible for the study, from whom 1928 (15.4%) had Blastocystis sp. infection. 170 cases (infected) and 170 controls (non-infected) were randomly selected for inclusion. Most of the participants were females (60.6%), with a median age of 46.7 (17-88) years. 126 (37.1%) of them were immigrants, mostly from America (20.3%), and had been living in Spain for 11 years, on average. 171 (50.3%) patients had travelled out of Spain the year before the sampling, mostly to European countries (19.4%). The majority of individuals had jobs with direct contact with other people (health personnel, teachers, caregivers) (85.6%) and 29.4% of individuals were in usual contact with animals (mostly dogs and cats). Regarding clinical information, 68.2% of patients presented digestive symptoms at the time of stool analysis, 3.5% presented an immunosuppressed status and 6.5% were infected by other parasites. When comparing cases with controls in the multivariate analysis, variables associated to Blastocystis sp. infection were: being born in Africa (p=0.012, OR 5.216), having travelled abroad (p=0.004, OR 1.932) and working in direct contact with other people (p=0.004, OR 2.654). However, having an intestinal parasitic co-infection seems to have a protective value (p=0.046, OR 0.37). Conclusions. Significant risk factors detected in the present study include having an African origin, working directly with the public and recent travelling are risk factors for acquiring Blastocystis sp. infection. Our study provides new insights into the epidemiology of Blastocystis sp. infection in industrialized countries, although larger and prospective studies must be performed