Journal Article > Short ReportFull Text
Science. 2011 December 9; Volume 334 (Issue 6061); DOI:10.1126/science.1210554
Bharti N, Tatem AJ, Ferrari MJ, Grais RF, Djibo A, et al.
Science. 2011 December 9; Volume 334 (Issue 6061); DOI:10.1126/science.1210554
Measles epidemics in West Africa cause a significant proportion of vaccine-preventable childhood mortality. Epidemics are strongly seasonal, but the drivers of these fluctuations are poorly understood, which limits the predictability of outbreaks and the dynamic response to immunization. We show that measles seasonality can be explained by spatiotemporal changes in population density, which we measure by quantifying anthropogenic light from satellite imagery. We find that measles transmission and population density are highly correlated for three cities in Niger. With dynamic epidemic models, we demonstrate that measures of population density are essential for predicting epidemic progression at the city level and improving intervention strategies. In addition to epidemiological applications, the ability to measure fine-scale changes in population density has implications for public health, crisis management, and economic development.
Journal Article > ResearchFull Text
Epidemiol Infect. 2011 October 5; Volume 140 (Issue 8); 1356-1365.; DOI:10.1017/S0950268811002032
Bharti N, Broutin H, Grais RF, Ferrari MJ, Djibo A, et al.
Epidemiol Infect. 2011 October 5; Volume 140 (Issue 8); 1356-1365.; DOI:10.1017/S0950268811002032
Throughout the African meningitis belt, meningococcal meningitis outbreaks occur only during the dry season. Measles in Niger exhibits similar seasonality, where increased population density during the dry season probably escalates measles transmission. Because meningococcal meningitis and measles are both directly transmitted, we propose that host aggregation also impacts the transmission of meningococcal meningitis. Although climate affects broad meningococcal meningitis seasonality, we focus on the less examined role of human density at a finer spatial scale. By analysing spatial patterns of suspected cases of meningococcal meningitis, we show fewer absences of suspected cases in districts along primary roads, similar to measles fadeouts in the same Nigerien metapopulation. We further show that, following periods during no suspected cases, districts with high reappearance rates of meningococcal meningitis also have high measles reintroduction rates. Despite many biological and epidemiological differences, similar seasonal and spatial patterns emerge from the dynamics of both diseases. This analysis enhances our understanding of spatial patterns and disease transmission and suggests hotspots for infection and potential target areas for meningococcal meningitis surveillance and intervention.
Journal Article > ResearchAbstract
Epidemiol Infect. 2010 September 1; Volume 138 (Issue 9); DOI:10.1017/S0950268809991385
Bharti N, Djibo A, Tatem AJ, McCabe CA, Bjørnstad ON, et al.
Epidemiol Infect. 2010 September 1; Volume 138 (Issue 9); DOI:10.1017/S0950268809991385
Though largely controlled in developed countries, measles remains a major global public health issue. Regional and local transmission patterns are rooted in human mixing behaviour across spatial scales. Identifying spatial interactions that contribute to recurring epidemics helps define and predict outbreak patterns. Using spatially explicit reported cases from measles outbreaks in Niger, we explored how regional variations in movement and contact patterns relate to patterns of measles incidence. Because we expected to see lower rates of re-introductions in small, compared to large, populations, we measured the population-size corrected proportion of weeks with zero cases across districts to understand relative rates of measles re-introductions. We found that critical elements of spatial disease dynamics in Niger are agricultural seasonality, transnational contact clusters, and roads networks that facilitate host movement and connectivity. These results highlight the need to understand local patterns of seasonality, demographic characteristics, and spatial heterogeneities to inform vaccination policy.