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University Park, PA 16802
My work examines the underlying mechanisms for spatial heterogeneities in host disease burden and risk across spatial scales, from regional dynamics to seasonal outbreaks in cities, rural villages, and across borders by assessing regional variations in movement and contact patterns relating to outbreaks and access to health care.
Changes in local population density and patterns of human movement are critical elements of disease dynamics that are often overlooked in both theoretical analyses and field studies because they can be extremely difficult to measure, particularly at epidemiologically relevant spatial and temporal scales.
While classical sociological and anthropological methods can characterize social determinants of epidemiological patterns, they can be ill suited for epidemiological studies and public health policy-making due to infrequent data collection and small sample sizes. To address this gap, my work synthesizes ideas from anthropology, biology, and geography to develop methods for identifying routes of movement and measuring rapid changes in population density. These represent key social and biological determinants of the spread and persistence of infectious diseases that weigh heavily on the efficacy of public health interventions but remain understudied.
Changes in the characteristics of human settlements can be seen either as determinants of health outcomes or as reactions to disruptive events. In the former scenario, human movement affects the risk of disease exposure and patterns of transmission as well as access to vaccination and health care services; in the latter, disease outbreaks, natural disasters, or political instability trigger human movement, displacement, or health care seeking behavior. Understanding both of these important aspects of human movement can aid in the development and refinement of predictive and reactive tools for public health interventions. Working with ministries of health, locally operating NGOs, and community leaders, I use satellite imagery and mobile phone usage data to measure large-scale movement and its impacts on health measures and surveys to ground-truth these findings.
Active study sites: Kaokoveld, Namibia; Niamey, Niger; Detroit, Michigan
Human movement measured from satellite imagery, mobile phone usage, and surverys; access to health care; and transmissible pathogens that impact humans including measles, meningitis, Herpes Simples I and II, microbiota, and others.
Bharti, N., Djibo, A., Grais, R., Tatem, A., Grenfell, B., Ferrari, M. (2016) Measuring populations to improve vaccination coverage. Scientific Reports 6:34541, DOI: 10.1038/srep34541
Bharti, N., Lu, X., Bengtsson, L., Wetter, E., Tatem, A. Remotely measuring populations during a crisis by overlaying two data sources. (2015) International Health 7(2):90-98. doi: 10.1093/inthealth/ihv003
Halloran, M.E, Vespignani, A., Bharti, N., Feldstein LR, Alexander KA, Ferrari MJ, Shaman J, Drake JM, Porco T, Eisenberg JNS, Del Valle SY, Lofgren E, Scarpino SV, Eisenberg MC, Gao D, Hyman JM, Eubank S, Longini RM. (2014) Ebola: Mobility data. Science 346(6208):433
Bharti, N. (2014) The importance of movement in environmental change and infectious disease. Institute of Medicine's Forum on Microbial Threats workshop summary on The Influence of Global Environmental Change on Infectious Disease Dynamics.
Lu, X., Wetter, E., Bharti, N., Tatem, A., Bengtsson, L. (2013) Approaching the limits of predictability in human mobility. Nature, Scientific Reports. 3(2923):1-9. doi:10.1038/srep02923
Tatem, A., Adamo, S., Bharti, N., Burgert, C., Castro, M., Dorelien, A., Fink, G., Linard, C., Mendelsohn J., Montana, L., Montgomery, M., Nelson, A., Noor, A., Pindolia, D., Yetman G., and Balk, D. (2012) Mapping populations at risk: improving spatial demographic data for infectious disease modeling and metric derivation. Population Health Metrics 10(8):1-14 doi:10.1186/1478-7954-10-8 Review Article
Bharti, N., Tatem A., Ferrari, M., Grais, R., Djibo, A., Grenfell, B. (2011) Explaining seasonal fluctuations of measles in Niger using nighttime lights imagery. Science 334(6061):1424-1427. doi: 10.1126/science.1210554
Bharti, N., Broutin, H., Ferrari, M., Grais, R., Djibo, A., Tatem, A., Grenfell, B. (2011) Spatial dynamics of meningitis in Niger: observed patterns in comparison with measles. Epidemiology and Infection doi:10.1017/S0950268811002032
Metcalf, C.J.E., Bjornstad, O.N., Ferrari, M.J., Klepac, P., Bharti, N., Lopez-Gatall, H., Grenfell, B.T. (2010) The epidemiology of rubella in Mexico: seasonality, stochasticity, and regional variation. Epidemiology and Infection 139:1029-1038.
Ferrari, M., Djibo, A., Grais, R.F., Bharti, N., Grenfell, B.T., Bjornstad, O.N. (2010) Rural-urban gradient in seasonal forcing of measles transmission in Niger. Proc Biol Sci 277(1695):2775-82.
Bharti, N., Djibo, A., Ferrari, M., Grais, R., Tatem, A., McCabe, C., Bjornstad, O., Grenfell, B. (2010) Measles hotspots and epidemiological connectivity in Niger. Epidemiology and Infection, 38(9):1308-16. doi: 10.1017/S0950268809991385
Bharti, N., Xia, Y., Bjornstand, O., Grenfell, B. (2008) Measles on the edge: coastal heterogeneities and disease modeling. PloS ONE 3(4): e1941. doi:10.1371/journal.pone.0001941
Ferrari, M., Grais, R., Bharti, N., Conlan, A., Bjornstand, O., Wolfson, L., Guerin., P., Djibo, A., Grenfell, B. (2008) The dynamics of measles in sub-Saharan Africa. Nature 451, 679-684. doi:10.1038/nature06509
Finkelman, B., Viboud, C., Koelle, K., Ferrari, M., Bharti, N., Grenfell, B. (2007) Global patterns in seasonal activity of influenza A/H3N2, A/H1N1, and B from 1997 to 2005: Viral coexistence and latitudinal gradients. PloS ONE 2(12): e1296. doi:10:1371/journal.pone.0001296