[The Cohort of the Spanish HIV Research Network (CoRIS) and its associated biobank; organizational issues, main findings and losses to follow-up].

INTRODUCTION: This article describes the development of the Cohort of the Spanish Research Network (CoRIS), its methodological and organizational aspects, the demographic and clinical characteristics of the subjects enrolled and quantifies the losses to follow-up and associated factors.
METHODS: Multicentre cohort of HIV-positive naïve subjects recruited in 28 sites of Spain from 2004-onwards. Missing and inconsistent data were submitted to internal quality controls and the datasets were externally audited. Multiple logistic regression models were used.
RESULTS: As of October 2009, 5,514 subjects had been recruited, representing 11,708 person-years with a median follow-up time of 1.81 years. Most are men (78.8%), infected by sexual transmission (46.1% men who have sex with men and 35.2% heterosexual persons) and Spanish (69.7%). During follow-up 64.5% have started Antiretroviral Therapy (ART) and 201 deaths have occurred. New HIV diagnoses accounted for 80.7% of the sample. Some 52% of subjects had at least one baseline sample in the BioBank while naïve to ART. Losses to follow-up (18.9%) were more frequent in younger people, in injecting drug users, in persons of non-Spanish origin, in persons with primary or lower educational level, and in those with a CD4 count over 350 cells/mm(3) at time of recruitment.
CONCLUSIONS: The implementation of CoRIS has been successful; the cohort has wide representation at national level, is actively recruiting new members and blood samples, and has excellent data quality. Losses to follow-up are of similar magnitude to other cohort studies, as are the factors associated with them.