Figure 1.

Percent of porcine reproductive and respiratory syndrome virus (PRRSV)-positive submissions reported at the Swine Disease Reporting System (SDRS) project over time and apparent seasonal pattern of detection of PRRSV over time. The seasons are organized by months: winter (Wi) = December, January, and February; spring (Sp) = March, April, and May; summer (Su) = June, July, and August; fall (Fa) = September, October, and November. For the SDRS database, a full 4-season cycle starts December 1 and ends November 30 of the subsequent year.