Relating diarrheal disease to social networks and the geographic configuration of communities in rural Ecuador

Abstract

Social networks and geographic structures of communities are important predictors of infectious disease transmission. To examine their joint effects on diarrheal disease and how these effects might develop, the authors analyzed social network and geographic data from northern coastal Ecuador and examined associations with diarrhea prevalence. Between July 2003 and May 2005, 113 cases of diarrhea were identified in nine communities. Concurrently, sociometric surveys were conducted, and households were mapped with geographic information systems. Spatial distribution metrics of households within communities and of communities with respect to roads were developed that predict social network degree in casual contact ("contact") and food-sharing ("food") networks. The mean degree is 25-40% lower in communities with versus without road access and 66-94% lower in communities with lowest versus highest housing density. Associations with diarrheal disease were found for housing density (comparing dense with dispersed communities: risk ratio = 3.3, 95% confidence interval (CI): 1.1, 10.0) and social connectedness (comparing lowest with highest degree communities: risk ratio = 3.4, 95% CI: 1.1, 10.1 in the contact network and risk ratio = 4.9, 95% CI: 1.1, 21.9 in the food network). Some of these differences may be related to more new residents, lower housing density, and less social connectedness in road communities.

FIGURE 1

Mean spatial index versus mean network degree in the community for contact (filled circles and solid line) and food (unfilled circles and dashed line) networks, Ecuador, 2003-2005. There were nine communities. The mean spatial index is the geometric mean distance of one household to all others in the community, and the mean network degree is the average number of community members nominated by the interviewee. Refer to Materials and Methods for more details. Data points under “Roadless communities” represent those communities without road access; those under “Road communities” represent communities that reside on the road.

FIGURE 2

Decay of probability of a social connection with distance between two houses in the contact (solid line) and food (dashed line) networks, Ecuador, 2003-2005. In communities 1, 2, and 4 (top row), the scale is 0 and 0.8. In the remainder of the communities, the scale is 0 and 0.5. Community 3 had only 84 connections in the contact network between 210 house pairs, while community 9 (not included in figure) had only two connections in the food network and 24 connections in 66 house pairs in the contact network, making the relations between distance and specific social connections difficult to discern.

FIGURE 3

Point estimates of diarrheal incidence as predicted by a multivariate model including both geographic and social factors, Ecuador, 2003-2005. Estimates are shown for the lowest and highest observed spatial indices, contact degrees, and food degrees. Risk ratios (RRs) are ratios between the lowest and the highest as predicted by a log-linear multivariate model. Numbers in parentheses, 95% confidence interval.