Socio-economic factors and its influence on the association between temperature and dengue incidence in 61 Provinces of the Philippines, 2010–2019

Background: Temperature has a significant impact on dengue incidence, however, changes on the temperature-dengue relationship across axes of socio-economic vulnerability is not well described. This study sought to determine the association between dengue and temperature in multiple locations in the Philippines and explore the effect modification by socio-economic factors. Method: Nationwide dengue cases per province from 2010 to 2019 and data on temperature were obtained from the Philippines’ Department of Health–Epidemiological Bureau and ERA5-land, respectively. A generalized additive mixed model (GAMM) with a distributed lag non-linear model was utilized to examine the association between temperature and dengue incidence. We further implemented an interaction analysis in determining how socio-economic factors modify the association. All analyses were implemented using R programming. Results: Nationwide temperature-dengue risk function was noted to depict an inverted U-shaped pattern. Dengue risk increased linearly alongside increasing mean temperature from 15.8 degrees Celsius and peaking at 27.5 degrees Celsius before declining. However, province-specific analyses revealed significant heterogeneity. Socio-economic factors had varying impact on the temperature-dengue association. Provinces with high population density, less people in urban areas with larger household size, high poverty incidence, higher health spending per capita, and in lower latitudes were noted to exhibit statistically higher dengue risk compared to their counterparts at the upper temperature range. Conclusions: This observational study found that temperature was associated with dengue incidence, and that this association is more apparent in locations with high population density, less people in urban areas with larger household size, high poverty incidence, higher health spending per capita, and in lower latitudes. Differences with socio-economic conditions is linked with dengue risk. This highlights the need to develop interventions tailor-fit to local conditions. Author summary: This study examined the effect of temperature on dengue in the 61 Provinces of the Philippines. We found that as temperature increases, so does the risk of dengue. However, the increase in the risk of dengue plateaus at 27.5 degrees Celsius, and beyond that temperature the risk decreases. The association between temperature and dengue incidence at high temperatures was stronger among provinces with high population density, less people in urban areas with larger household size, high poverty incidence, higher health spending per capita, and in lower latitudes compared to their counterparts. In particular, results showed that people in the rural areas had higher dengue risk than those in urban areas, which is contrary to expectations that dengue is an urban-dwelling related disease. On another hand, we found that high health spending per capita does not equate to better health outcomes. Efficiency of use of resources may come into play in terms of improving the health outcomes and not just the quantity or amount of the difference in the dengue risk by socio-economic factors highlights the need for a tailor-fit dengue response.