TY - JOUR T1 - Real-time Zika risk assessment in the United States JF - bioRxiv DO - 10.1101/056648 SP - 056648 AU - Lauren A Castro AU - Spencer J Fox AU - Xi Chen AU - Kai Liu AU - Steve Bellan AU - Nedialko B Dimitrov AU - Alison P Galvani AU - Lauren Ancel Meyers Y1 - 2016/01/01 UR - http://biorxiv.org/content/early/2016/09/07/056648.abstract N2 - Recent Zika Virus (ZIKV) outbreaks in southern Florida have heightened public health concern across the southern United States. As autochthonous (locally-acquired) cases accumulate within the US, policymakers seek early and accurate indicators of self-sustaining transmission to inform intervention efforts in high risk areas. However, given ZIKV’s low reporting rates and the geographic variability in both importations and transmission potential, a small cluster of reported cases may reflect diverse scenarios, ranging from multiple self-limiting but independent introductions to a self-sustaining local epidemic. We developed a stochastic model that captures variation and uncertainty in ZIKV case reporting, importations, and transmission, and applied it to assess county-level epidemic risk throughout the state of Texas. For each of the 254 counties, we estimated the future epidemic risk as a function of reported autochthonous cases and evaluated a national recommendation to trigger interventions immediately following the first two reported cases of locally-transmitted ZIKV. Our analysis suggests that the regions of greatest risk for sustained ZIKV transmission include 21 Texas counties along the Texas-Mexico border, in the Houston Metro Area, and throughout the I-35 Corridor from San Antonio to Waco. Variation in vector habitat suitability and importation risk drives epidemic risk variation. Upon detection of two locally transmitted cases in a spatiotemporal cluster, the threat of epidemic expansion depends critically on local vulnerability. For high risk Texas counties, we estimate this likelihood to be 64%, assuming an August 2016 risk projection and a 20% reporting rate. With reliable estimates of key epidemiological parameters, including reporting rates and vector abundance, this framework can help optimize the timing and spatial allocation of public health resources to fight ZIKV in the US.Author Summary Given the growing threat of Zika Virus (ZIKV) in the southern US and the critical importance of early intervention, public health decision makers seek early and accurate indicators of local transmission. However, given ZIKV’s low reporting rates and the geographic variability in both importations and transmission potential, a small cluster of reported cases may reflect diverse scenarios, ranging from multiple self-limiting but independent introductions to a self-sustaining local epidemic. To support realtime risk assessment of emerging ZIKV outbreaks at a county level, we developed a quantitative framework that estimates current ZIKV burden and future epidemic threat based on recent reported cases and the underlying risks of ZIKV importation and transmission. We assessed ZIKV risk in Texas and found that 21 of the 254 counties are potentially vulnerable to locally-transmitted ZIKV outbreaks. The high risk region includes much of the Texas-Mexico border, the Houston Metro Area, and patches along the I-35 Corridor from San Antonio to Waco. If two locally transmitted and epidemiologically linked cases are detected in one of these counties, we estimate a 64% risk of imminent epidemic expansion. ER -