Understanding the early dynamics of the 2014 porcine epidemic diarrhea virus (PEDV) outbreak in Ontario using the incidence decay and exponential adjustment (IDEA) model

Greer, Amy L.; Spence, Kelsey; Gardner, Emma

Lastly, it has been proposed that the publically reported data available through OMAFRA may in fact be under-reported by virtue of the fact that for some producers, the laboratory confirmed status documented in the dataset represents only the initial or index farm case within individual production systems (with some production systems being comprised of many individual farms or premises). For instance, a farrow-to-wean farm may test positive for PEDV and some of those infected pigs may move to other farms within the production system causing downstream infections at receiving facilities (e.g. finisher herds etc.). These subsequent downstream farms that become infected may not appear in the OMAFRA dataset as the movement of pigs and subsequent clinical disease in other farms within the same production system occur within a system that is already aware of the PEDV status of the index farm within the production system. The treatment of downstream pigs and enhanced biosecurity would likely be addressed without the submission of additional samples to the laboratory. To address the possibility of under-reporting in the dataset, we examined the potential impact of 25% and 50% under-reporting and found that even if the data represent only a subset of infected farms within Ontario, the model parameter estimates for R 0 and d remain relatively stable (Table 1 ) suggesting that the model is not overly sensitive to mild to moderate levels of under-reporting.