Heterogeneity of dengue transmission in an endemic area of Colombia.

Population based serological surveys are the gold-standard to quantify dengue (DENV) transmission. The purpose of this study was to estimate the age-specific seroprevalence and the force of infection of DENV in an endemic area of Colombia. Between July and October 2014, we conducted a household based cross-sectional survey among 1.037 individuals aged 2 to 40 years living in 40 randomly selected locations in urban Piedecuesta, Santander, Colombia. In addition, we also enrolled 246 indviduals living in rural "veredas". Participants were asked to answer a questionnaire that included demographic, socioeconomic and environmental questions and to provide a 5 ml blood sample. Sera were tested using the IgG indirect ELISA (Panbio) kit to determine past DENV infection. The overall DENV seroprevalence was 70% (95% CI = 67%-71%), but was significantly higher in urban (81%, 95% CI = 78%-83%) as compared to rural (21%, 95% CI = 17%-27%) locations. Age was a major predictor of seropositivity, consistent with endemic circulation of the virus. Using catalytic models we estimated that on average, 12% (95%CI = 11%-13%) of susceptible individuals living in the city are infected by DENV each year. Beyond age, the only predictor of seropositivity in urban locations was prior history of dengue diagnosed by a physician (aPR 1.15, 95% CI = 0.98–1.35). Among participants living in rural settings, those that reported traveling outside of their vereda were more likely to be seropositive (aPR 3.60, 95%CI = 1.54–8.42) as well as those who were born outside of Santander department (aPR = 2.77, 95%CI = 1.20–6.37). These results are consistent with long term endemic circulation of DENV in Piedecuesta, with large heterogeneities between urban and rural areas located just a few kilometers apart. Design of DENV control interventions, including vaccination, will need to consider this fine scale spatial heterogeneity. Author summary: Dengue is the most rapidly expanding arbovirus in the world. Counts of reported dengue cases, as usually reported by surveillance systems, are a poor metric of the underlying transmission because most of the infections are asymptomatic. Population based serological surveys, where the prevalence of antibodies to dengue virus are measured in a random sample of the population, are considered the gold-standard to quantify dengue transmission. In this study, the authors conducted a population based serological survey in urban and rural areas of Piedecuesta, Santander, Colombia. Seropositivity was significantly higher in urban as compared to rural locations. Age was a major predictor of seropositivity, consistent with long-term circulation of the virus in this setting. They estimated that, on average, 12% of susceptible individuals living in urban locations get infected by dengue each year. The only predictor of prior dengue infection in urban inhabitants was self-reported history dengue. In rural locations, traveling regularly outside of their "vereda" (neighborhood) and having been born outside of Santander department were associated with seropositivity. These results show that the Piedecuesta municipality is an endemic area of dengue transmission, with large heterogeneities between urban and rural settings. Control interventions, including vaccination should be targeted at fine spatial scales. [ABSTRACT FROM AUTHOR]