A Spatial Analytic Approach to Examine Community-Wide Shigella Transmission

William Pan, Johns Hopkins Bloomberg School of Public Health
Margaret Kosek, Johns Hopkins Bloomberg School of Public Health
Pablo Penataro Yori, Asociación Benéfica PRISMA (AB PRISMA)
Maribel Paredes Olortegui, Asociación Benéfica PRISMA (AB PRISMA)
Robert Gilman, Johns Hopkins Bloomberg School of Public Health and Asociación Benéfica PRISMA (AB PRISMA)

Diarrheal diseases are one of the leading causes of death worldwide among children under five. Among the enteric pathogens that cause diarrhea, shigella is particularly problematic due to its low infectious dose, potentially easing transmission. While person-to-person transmission is considered to occur through fecally contaminated hands, mechanical vectors -- predominantly houseflies -- are also considered a primary cause of transmission. This research draws upon a prospective longitudinal case-control surveillance study of children under five in the community of Santa Clara, Peru to examine factors associated with the transmission of shigella. Focusing on the hypothesis of fly-related shigella transmission, a model of fly density is developed using two-month time intervals over a three-year period, community-wide fly capture data, and daily rainfall data aggregated to the appropriate time interval. Spatial predictions are made to estimate fly densities throughout the community and a space-time model of shigella is developed to test the importance of fly density on shigella transmission.