Social and environmental risk factors for dengue in Delhi city: A retrospective study

Abstract

Global urbanization is leading to an inexorable spread of several major diseases that need to be stemmed. Dengue is one of these major diseases spreading in cities today, with its principal mosquito vector superbly adapted to the urban environment. Current mosquito control strategies are proving inadequate, especially in the face of such urbanisation and novel, evidence-based targeted approaches are needed. Through combined epidemiological and entomological approaches, we aimed to identify a novel sanitation strategy to alleviate the burden of dengue through how the dengue virus spreads through the community. We combined surveillance case mapping, prospective serological studies, year-round mosquito surveys, socio-economic and Knowledge Attitudes and Practices surveys across Delhi. We identified lack of access to tap water (≤98%) as an important risk factor for dengue virus IgG sero-positivity (adjusted Odds Ratio 4.69, 95% C.I. 2.06–10.67) and not poverty per se. Wealthier districts had a higher dengue burden despite lower mosquito densities than the Intermediary income communities (adjusted Odds Ratio 2.92, 95% C.I. 1.26–6.72). This probably reflects dengue being introduced by people travelling from poorer areas to work in wealthier houses. These poorer, high density areas, where temperatures are also warmer, also had dengue cases during the winter. Control strategies based on improved access to a reliable supply of tap water plus focal intervention in intra-urban heat islands prior to the dengue season could not only lead to a reduction in mosquito abundance but also eliminate the reservoir of dengue virus clearly circulating at low levels in winter in socio-economically disadvantaged areas.

Challenges to Mitigating the Urban Health Burden of Mosquito-Borne Diseases in the Face of Climate Change

“…[ 29 , 30 ]. Whilst generally considered at the city vs. neighboring rural environment scale, the effects of urban geometry, both with the shading effect in daytime and with the reduction of radiative cooling and increasing thermal storage at night, can generate differences in UHI intensity at a very local scale [ 31 , 32 ].…”

“…Managing water resources is predicted to become a serious problem, especially in the urban setting and inadequate permanent access to water leads to water storage practices that enables proliferation of mosquito populations and increased disease [ 32 ]. Lack of piped water has been shown to be a risk factor for dengue and is likely also to be the case for urban malaria [ 32 ]. In this case, strategies to improve water supplies could lead to sectorial co-benefits.…”

The Challenge of Controlling Urban Mosquito-Borne Diseases in a Changing Urban Climate

“…All these features will affect evaporative cooling and convection efficiency transferring heat to the lower atmosphere [67]. Whilst generally considered at the city vs. neighbouring rural environment scale, even at small intra-urban scales, the effects of urban geometry, both with the shading effect in daytime and with the reduction of radiative cooling and increasing thermal storage at night, can generate differences in UHI intensity at a very local scale [32,68]. During the daytime, the UHI intensity is largely influenced by convection efficiency associated with surface roughness and changes in the partitioning of latent or sensible heat fluxes associated with local climate-vegetation characteristics [69,70].…”

“…Managing water resources is predicted to become a serious problem, especially in the urban setting and inadequate permanent access to water leads to water storage practices that enables proliferation of mosquito populations and increased disease [68]. In this case, strategies to improve water supplies could lead to sectorial co-benefits.…”

“…Whilst other new control methods are showing promise [91], mitigating against urban vector-borne diseases could use the leverage of other sectors impacted upon by climate change -notably water, environmental/ecosystem hygiene and urban geometry. Lack of piped water has been shown to be a risk factor for dengue and is likely also to be the case for urban malaria [68]. It is also a clear concern for drinking water quality generally.…”