===== Spatio-Temporal Modelling of Climate-Sensitive Disease Risk: Towards an Early Warning System for Dengue in Brazil =====


  The transmission of many infectious diseases is affected by weather and climate variations, particularly 
  for diseases spread by arthropod vectors such as malaria and dengue. In recent years, epidemiological
  studies have demonstrated statistically significant associations between infectious disease incidence 
  and climate variability. Such research has highlighted the potential for developing climate-based 
  epidemic early warning systems. This presentation proposes a framework to model spatio-temporal variation 
  in disease risk using both climate and non-climate information. The framework is developed in the context 
  of dengue fever in Brazil. Dengue is currently one of the most important emerging tropical diseases and 
  dengue epidemics impact heavily on Brazilian public health services.

  A negative binomial generalised linear mixed model (GLMM) is adopted which makes allowances for unobserved 
  confounding factors by including spatially structured and unstructured random effects. The model
  successfully accounts for the large amount of overdispersion found in disease counts. The parameters 
  in this spatio-temporal Bayesian hierarchical model are estimated using Markov Chain Monte Carlo (MCMC).
  This allows posterior predictive distributions for disease risk to be derived for each spatial location 
  and time period (month/season). Given decision and epidemic thresholds, probabilistic forecasts can be issued,
  which are useful for developing epidemic early warning systems. The potential to provide useful early warnings 
  of future increased and geographically specific dengue risk is investigated. The predictive validity of the 
  model is evaluated by fitting the GLMM to data from 2001-2007 and comparing probabilistic predictions to 
  the most recent out-of-sample data in 2008-2009. For a probability decision threshold of 30% and the pre-defined 
  epidemic threshold of 300 cases per 100,000 inhabitants, successful epidemic alerts would have been issued for 
  94% of the 54 microregions that experienced high dengue incidence rates in South East Brazil, during 
  February - April 2008.