Abstract
Porcine epidemic diarrhea virus (PEDV) emerged in the United States (U.S.) swine population in 2013, initiating an initial significant epidemic followed by a state of endemicity in the U.S. Despite continued monitoring, the epidemiology of PEDV during its endemic phase remains inadequately researched. Our study aimed to characterize the spatial-temporal distribution of postepidemic PEDV cases in the U.S. breeding herd and identify associated risk factors. Data from 1089 breeding farms in 27 states, reported to the Morrison Swine Health Monitoring Project from July 2014 to June 2021, were analyzed. We stratified the data into six U.S. regions and employed SaTScan for spatiotemporal permutation and cluster analysis. Survival analysis was used to assess risk factors. A notable seasonal clustering of PEDV cases was observed in winter (January-March; p=0.001, relative risk = 2.2) with regional variation. Ten high-rate spatial-temporal clusters (p < 0.05) were identified ranging from 2.5 to 833.7 km(2) and lasting 1-5 months, occurring in four regions between 2015 and 2021. For the study period, a total of 625 cases of PEDV were recorded on 372 farms. The total number of PEDV cases decreased from 95 breeding farms in 32 counties (2014-2015) to 53 farms in 28 counties (2020-2021), indicating an overall reduction in occurrence and spatial extent. Feed mitigants demonstrated a protective effect, significantly reducing the risk of PEDV occurrence (hazard ratio = 0.3, p=0.003), while air filtration systems exhibited marginal benefits (hazard ratio = 0.3, p=0.06). Other important risk factors included county farm density with farms in high-density regions (>31 farms/100 km(2)) being 1.3 times more likely to experience outbreaks than in medium-density regions (13-31 farms/1000 km(2); p < 0.001). Additionally, farms in region E had higher odds of outbreaks compared to region B. The overall decline in PEDV cases and reduced spatial extent reflect industry efforts in postepidemic control and elimination. The protective effects of feed mitigants warrant further investigation. Our findings underscore the opportunity for coordinated efforts to eliminate PEDV in the U.S. and emphasize the need for comprehensive risk profiling associated with industry practices.