Dengue outlook for the World Cup in Brazil: an early warning model framework driven by real-time seasonal climate forecasts

Background With more than a million spectators expected to travel among 12 different cities in Brazil during the football World Cup, June 12-July 13,2014, the risk of the mosquito-transmitted disease dengue fever is a concern. We addressed the potential for a dengue epidemic during the tournament, using a probabilistic forecast of dengue risk for the 553 microregions of Brazil, with risk level warnings for the 12 cities where matches will be played. Methods We obtained real-time seasonal climate forecasts from several international sources (European Centre for Medium-Range Weather Forecasts [ECMWF], Met Office, Meteo-France and Centro de Previsao de Tempo e Estudos Climaticos [CPTEC]) and the observed dengue epidemiological situation in Brazil at the forecast issue date as provided by the Ministry of Health. Using this information we devised a spatiotemporal hierarchical Bayesian modelling framework that enabled dengue warnings to be made 3 months ahead. By assessing the past performance of the forecasting system using observed dengue incidence rates for June, 2000-2013, we identified optimum trigger alert thresholds for scenarios of medium-risk and high-risk of dengue. Findings Our forecasts for June, 2014, showed that dengue risk was likely to be low in the host cities Brasilia, Cuiaba, Curitiba, Porto Alegre, and Sao Paulo. The risk was medium in Rio de Janeiro, Belo Horizonte, Salvador, and Manaus. High-risk alerts were triggered for the northeastern cities of Recife (P-high=19%), Fortaleza(P-high=46%), and Natal (P-high=48%). For these high-risk areas, particularly Natal, the forecasting system did well for previous years (in June, 2000-13). Interpretation This timely dengue early warning permits the Ministry of Health and local authorities to implement appropriate, city-specific mitigation and control actions ahead of the World Cup.