Distance to public transit predicts spatial distribution of dengue virus incidence in Medellín, Colombia

Abstract

Dengue is a growing global threat in some of the world's most rapidly growing landscapes. Research shows that urbanization and human movement affect the spatial dynamics and magnitude of dengue outbreaks; however, precise effects of urban growth on dengue are not well understood because of a lack of sufficiently fine-scaled data. We analyzed nine years of address-level dengue case data in Medellin, Colombia during a period of public transit expansion. We correlate changes in the spread and magnitude of localized outbreaks to changes in accessibility and usage of public transit. Locations closer to and with a greater utilization of public transit had greater dengue incidence. This relationship was modulated by socioeconomic status; lower socioeconomic status locations experienced stronger effects of public transit accessibility and usage on dengue incidence. Public transit is a vital urban resource, particularly among low socioeconomic populations. These results highlight the importance of public health services concurrent with urban growth.

Figure 1

Maps of the transport zones of Medellín showing (A) mean socioeconomic status per zone, and (B) mean elevation per zone in meters. Blank zones are zones for which there was no data available. Socioeconomic status is measured as Estrato, a scale used for socioeconomic classification by the government of Colombia, measuring from 1 (lowest) to 6 (highest). Figure created in R (version 3.4.1) (R Core Team https://www.R-project.org/).

Figure 2

Maps of Medellin, Colombia 2008–2016. Each panel shows the relative distribution of dengue incidence per zone. Relative dengue incidence is shown using the Getis Ord Local G statistic to enable comparisons across years with large differences in the number of total dengue cases. The public transit lines available in each year are shown as black lines for the Metro, Metroplus, Rutas Alimentadoras, and the Escaleras Electricas. In (A) 2008, (B) 2009, and (C) 2010, two metro lines, Lines (A) and (B), and two arial cable car (Metrocable) lines, Lines J and K were available. In (D) 2011, Metroplus Linea 1 was added. The Metroplus is a bus line with dedicated constructed lanes and stops that connects directly with the metro. In (E) 2012 the Escaleras electricas began operating. The escaleras electricas are a system of public transit escelators. Their inauguration was on December 28, 2011, but they are analyzed here with 2012 data. In (F) 2013, no new lines were added. In (G) 2014 the Metroplus Linea 2 and Rutas Alimentadoras were addded. The Metroplus Linea 2 runs along the same route as the Linea 1 but more than doubles the capacity of the Metroplus system. The Rutas Alimentadoras are bus lines operated by the city that feed into the metro and Metroplus systems and do not run on dedicated lanes. In (H) 2015, no new lines were added. In (I) 2016, a Tranvia line and a Metrocable line, Line (H) were added. The tranvia is a monorail line. Figure created in R (version 3.4.1) (R Core Team https://www.R-project.org/).