Lack of access to water reveals dengue hotspots in megacities

In highly urban areas, lack of access to tap water is a strong predictor for dengue infection, particularly in the most socially disadvantaged communities, according to a recent study.

“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 socioeconomically disadvantaged areas,” the researchers said.

Focusing on Delhi City, India, the researchers combined epidemiological and entomological approaches: surveillance case mapping, prospective serological monitoring, socioeconomic and Knowledge Attitudes and Practices (KAP) surveys, and year-round mosquito surveillance. Overall, 2,107 individuals across 18 city colonies—administrative units—were sampled, all of whom were within the vicinity of an index dengue case.

A total of 160 participants were found to be positive for dengue immunoglobulin (Ig) M or the nonstructural protein 1 (NS1) antigen, suggesting that 7.6 percent of participants had probable recent or current infection, respectively. [PLoS Negl Trop Dis 2021;15:e0009024]

Dividing Delhi into clusters according to socioeconomic status (SES), the researchers found that deprived, high-density (HD) saw a significantly greater risk of recent dengue infection than communities that were also deprived, but not highly dense (adjusted odds ratio [aOR] for deprived vs deprived HD, 0.32, 95 percent confidence interval [CI], 0.10–0.98; p=0.047).

Similarly, those in intermediary units saw a significantly lower risk of recent dengue infection as compared to their deprived HD counterparts (aOR, 0,32, 95 percent CI, 0.14–0.73; p=0.007). Notably, such a risk did not differ between the deprived HD and wealthy communities (adjusted OR, 0.93, 95 percent CI, 0.44–1.97; p=0.844).

The definition of SES was based on a property tax scale, calculated via 10 criteria including access to urban physical and social infrastructures and rent values. Deprived communities were those that scored <40 points on the scale; intermediary units scored between 40–65 and wealthy areas scored >65 points.

Robust access to tap water emerged as a better predictor of dengue risk. Compared to communities with >98-percent access, all other categories, representing lower levels of access, saw significant and increasing risks of dengue.

For instance, those with 93–98 percent tap water access had an aOR of 2.29 (95 percent CI, 1.14–4.59; p=0.043), which jumped to 4.69 (95 percent CI, 2.06–10.7; p<0.001) in colonies with only 24–60 percent access.

It is worth noting that very low levels of access to tap water only occurred in deprived HD neighbourhoods. Moreover, in poorer HD areas, average temperatures were also higher, such that there were detectable cases of dengue even during winter.

“The spread of disease recognizes no socioeconomic boundaries and eliminating sources of infection must be a priority, not only for the socially disadvantaged population, but for the urban community as a whole,” the researchers said. “In conclusion, there is an important need to put health at the centre of urban planning and not least provide access to tap water.”