Personalized Medicine in HCV Infection. A Prospective, Multicenter, Epidemiological Study to Evaluate the Prevalence of Hepatitis C Infection in Spain in 2015 (PREVHEP)

Design of the study: Seroepidemiological and virological study of cross-sectional population-based.

Patients and sampling: The study population has been distributed in groups according to age (20-34; 35-49; 50-74 years) and sex. In order to select a representative sample of this overall population, three Spanish regions will be selected on the basis of their different HCV-related hospitalisation rates defined as follows: high, >120 cases/100,000 inhabitants (Madrid); medium, 90-119 cases/100,000 inhabitants (Cantabria); or low, <90 cases/100,000 inhabitants (Valencia).

The participants will be selected through a random, representative sample using our two-stage conglomerate sampling with stratification of the First-Stage Units. These FSUs are made up by the Basic Health Areas (Health Centers). The Second-Stage Units are made up by the individuals. The stratification criteria used in the first stage will be the socioeconomic status-rural/urban environment. The selection of sample elements will be carried out through simple random sampling from the healthcare card database pertaining to the selected Health Centers. A sequence of random, computer-generated numbers will be obtained.

Sample size: In order to achieve an accuracy of 0.4% in the estimate of a percentage through a two-tailed 95% confidence interval, assuming the prevalences indicated by age strata in the general Spanish population (0.6%, 1.9% and 2.7% respectively), a total of 12,263 subjects distributed as follows: 1,456 aged 20-34 years, 4,476 aged 35-49 years and 6,331 aged 50-74 years.

Anticipating an uptake of 9-15%,21 following invitation via telephone, between 81,753 and 136,255 subjects distributed over the three regions needed to be contacted at random.