Ethical aspects This study will be conducted in accordance with the Declaration of Helsinki and the Colombian legislation, following the Ministry Of Health resolution No. 8430/93. Prior to the admission of the patients in the study, the objectives and the methodology will be explained and a written informed consent obtained. The present study has been approved by the Research Ethics Committee of the FCV (Act # 197/June 19/2009). The patients' right to confidentiality will be kept in all the phases of the study.