Spatial Epidemiology and Risk Factor Analysis of White Spot Disease in the Shrimp Farming Industry of Sinaloa, Mexico, from 2005 to 2011

White spot disease (WSD), caused by the white spot syndrome virus, is currently one of the primary causes of mortality and economic losses in the shrimp farming industry worldwide. In Mexico, shrimp production is one of the most important primary activities generating an annual income of USD 711 million. However, WSD introduction in 1999 had a devastating impact for the Mexican shrimp industry. The aim of this study was to characterize the WSD spatio-temporal patterns and to identify the primary risk factors contributing to WSD occurrence from 2005 to 2011 in Sinaloa, Mexico. We used data collected by the Comite Estatal de Sanidad Acuicola de Sinaloa' from 2005 to 2011 regarding WSD outbreaks as well as environmental, production and husbandry factors at farm level. The spatio-temporal patterns of WSD were described using space-time scan statistics. The effect of 52 variables on the time to WSD outbreak occurrence was assessed using a multivariable Cox proportional hazards model. Results reveal that WSD risk and survival time were not homogeneously distributed as suggested by the significant clusters obtained using the space-time permutation model and the space-time exponential model, respectively. The Cox model revealed that the first production cycle [hazard ratio (HR)=11.31], changes from 1 to 1.4 degrees C of temperature oscillation caused by El Nino'/'La Nina' events (HR=1.44) and high average daily growths (HR=1.26) were significantly associated with lower survival (i.e. shorter time to WSD outbreak) on farm. Conversely, shrimp weight at the moment of the outbreak (HR=0.159), changes from -0.9 to -0.5 degrees C of temperature oscillation caused by El Nino'/'La Nina' events (HR=0.540), high superficial water temperature during the pound stocking (HR=0.823) and high (>100) number of days of culture (HR=0.830) were factors associated with higher survival. Results are expected to inform the design of risk-based, intervention strategies to minimize the impact of WSD in Mexico.