Role of health determinants in a measles outbreak in Ecuador: A case-control study with aggregated data

Background: In 2011-2012, an outbreak of measles occurred in Ecuador. This study sought to ascertain which population characteristics were associated. Methods: Case-control study of aggregate data. The unit of analysis was the parish (smallest geographic division). The national communicable disease surveillance database was used to identify 52 case parishes (with at least one confirmed case of measles) and 972 control parishes (no cases of measles). A hierarchical model was used to determine the association of measles with population characteristics and access to health care. Results: Case parishes were mostly urban and had a higher proportion of children under 1 year of age, heads of household with higher educational attainment, larger indigenous population, lower rates of measles immunization, and lower rates of antenatal care visit attendance. On multivariate analysis, associations were found with educational attainment of head of household ≥8 years (OR: 0.29; 95%CI 0.15-0.57) and ≥1.4% indigenous population (OR: 3.29; 95%CI 1.63-6.68). Antenatal care visit attendance had a protective effect against measles (OR: 0.98; 95%CI 0.97-0.99). Measles vaccination was protective of the outbreak (OR: 0.97; 95%CI 0.95-0.98). The magnitude of these associations was modest, but represents the effect of single protective factors, capable of acting at the population level regardless of socioeconomic, biological, and environmental confounding factors. Conclusion: In Ecuador, the parishes with the highest percentage of indigenous populations and those with the lowest vaccination coverage were the most vulnerable during the measles outbreak.