This study will be conducted in accordance with the Declaration of Helsinki and with the Colombian legislation as per the Resolution 8430/93 from the Ministry of Health. 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 study was approved by the Research Ethics Committee of the FCV (Act# 075/April 27/2004). The patients' right to confidentiality will be maintained in all the phases of the study.