In Chile, in the contingent public debate about the alarming indicators of the prevalence of infectious diseases (such sexually transmitted ones), two factors stand out as determinants: inefficient or scarce preventive campaigns and the poor level of self-care among immigrants. To develop an analytical perspective, a simplified mathematical model is proposed that quantitatively expresses the impact of these factors. Furthermore, we intend to show how these factors working together act within the epidemic of the disease. Despite the simplicity of the proposed argument, a better understanding may address theoretical recommendations for the control and prevention of the disease.