title: Multilevel Analysis of Trachomatous Trichiasis and Corneal Opacity in Nigeria: The Role of Environmental and Climatic Risk Factors on the Distribution of Disease.
abstract: The distribution of trachoma in Nigeria is spatially heterogeneous, with large-scale trends observed across the country and more local variation within areas. Relative contributions of individual and cluster-level risk factors to the geographic distribution of disease remain largely unknown. The primary aim of this analysis is to assess the relationship between climatic factors and trachomatous trichiasis (TT) and/or corneal opacity (CO) due to trachoma in Nigeria, while accounting for the effects of individual risk factors and spatial correlation. In addition, we explore the relative importance of variation in the risk of trichiasis and/or corneal opacity (TT/CO) at different levels. Data from the 2007 National Blindness and Visual Impairment Survey were used for this analysis, which included a nationally representative sample of adults aged 40 years and above. Complete data were available from 304 clusters selected using a multi-stage stratified cluster-random sampling strategy. All participants (13,543 individuals) were interviewed and examined by an ophthalmologist for the presence or absence of TT and CO. In addition to field-collected data, remotely sensed climatic data were extracted for each cluster and used to fit Bayesian hierarchical logistic models to disease outcome. The risk of TT/CO was associated with factors at both the individual and cluster levels, with approximately 14% of the total variation attributed to the cluster level. Beyond established individual risk factors (age, gender and occupation), there was strong evidence that environmental/climatic factors at the cluster-level (lower precipitation, higher land surface temperature, higher mean annual temperature and rural classification) were also associated with a greater risk of TT/CO. This study establishes the importance of large-scale risk factors in the geographical distribution of TT/CO in Nigeria, supporting anecdotal evidence that environmental conditions are associated with increased risk in this context and highlighting their potential use in improving estimates of disease burden at large scales.
authors.affiliation: Department of Disease Control, Faculty of Infectious and Tropical Diseases, London School of Hygiene & Tropical Medicine, London, United Kingdom; Global Health Group, University of California San Francisco, San Francisco, California, United States of America.
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Smith
authors.affiliation: Medical Statistics Team, Division of Applied Health Sciences, University of Aberdeen, United Kingdom.
authors.forename: Selvaraj
authors.initials: S
authors.lastname: Sivasubramaniam
authors.affiliation: Prevention of Blindness Union, Riyadh, Saudi Arabia.
authors.forename: Mansur M
authors.initials: MM
authors.lastname: Rabiu
authors.affiliation: Department of Clinical Research, Faculty of Infectious and Tropical Diseases, London School of Hygiene & Tropical Medicine, London, United Kingdom; College of Health Sciences of University of Abuja, Abuja, Nigeria.
authors.forename: Fatima
authors.initials: F
authors.lastname: Kyari
authors.affiliation: Department of Clinical Research, Faculty of Infectious and Tropical Diseases, London School of Hygiene & Tropical Medicine, London, United Kingdom.
authors.forename: Anthony W
authors.initials: AW
authors.lastname: Solomon
authors.affiliation: Department of Clinical Research, Faculty of Infectious and Tropical Diseases, London School of Hygiene & Tropical Medicine, London, United Kingdom.
authors.forename: Clare
authors.initials: C
authors.lastname: Gilbert
mesh_terms: D000328:Adult; D017677:Age Distribution; D000368:Aged; D000369:Aged, 80 and over; D004777:Environment; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D055361:Multilevel Analysis; D009549:Nigeria / Q000453:epidemiology; D015995:Prevalence; D012307:Risk Factors; D012424:Rural Population / Q000706:statistics & numerical data; D014141:Trachoma / Q000453:epidemiology*; D058457:Trichiasis / Q000453:epidemiology* / Q000382:microbiology