Spatial analysis of dengue transmission in an endemic city in Brazil reveals high spatial structuring on local dengue transmission dynamics

Abstract

In the last decades, dengue has become one of the most widespread mosquito-borne arboviruses in the world, with an increasing incidence in tropical and temperate regions. The mosquito Aedes aegypti is the dengue primary vector and is more abundant in highly urbanized areas. Traditional vector control methods have showing limited efficacy in sustaining mosquito population at low levels to prevent dengue virus outbreaks. Considering disease transmission is not evenly distributed in the territory, one perspective to enhance vector control efficacy relies on identifying the areas that concentrate arbovirus transmission within an endemic city, i.e., the hotspots. Herein, we used a 13-month timescale during the SARS-Cov-2 pandemic and its forced reduction in human mobility and social isolation to investigate the spatiotemporal association between dengue transmission in children and entomological indexes based on adult Ae. aegypti trapping. Dengue cases and the indexes Trap Positive Index (TPI) and Adult Density Index (ADI) varied seasonally, as expected: more than 51% of cases were notified on the first 2 months of the study, and higher infestation was observed in warmer months. The Moran's Eigenvector Maps (MEM) and Generalized Linear Models (GLM) revealed a strong large-scale spatial structuring in the positive dengue cases, with an unexpected negative correlation between dengue transmission and ADI. Overall, the global model and the purely spatial model presented a better fit to data. Our results show high spatial structure and low correlation between entomological and epidemiological data in Foz do Iguaçu dengue transmission dynamics, suggesting the role of human mobility might be overestimated and that other factors not evaluated herein could be playing a significant role in governing dengue transmission.

Figure 1

Daily number of dengue cases reported in children with less than 10 years in the city of Foz do Iguaçu between March 2020 to March 2021. This period comprises the SARS-CoV-2 pandemic when children have limited mobility due to social restrictions. Each color represents 2 months of epidemiological data associated with the entomological surveys, except for March 2021, when mobility limitations were relaxed.

Figure 2

Map of Foz do Iguaçu showing the spatial distribution of dengue cases. Colors in the pie chart are associated with the bimonthly larval surveys, using the same colors as in Fig. 1.

Figure 3

Entomological indexes based on adult Aedes aegypti sampling in the city of Foz do Iguaçu between March 2020 to March 2021. (A) Trap Positive Index, TPI; (B) Adult Density Index, ADI. Each dot represents the index value in one of the 73 study areas, whereas the red dot represents the mean value of each survey.

Figure 4

Number of dengue cases reported in children with less than 10 years in the city of Foz do Iguaçu between March 2020 to March 2021. (A) Notification; (B) Notification_4wk; (C) Notification + Confirmation; (D) Notification + Confirmation_4wk. Figure was constructed using a Kernel smoothing with quartic function and width of 1000 m. i.e., the influence of a point decreases as the distance from the point increases.