Fig. 1

a Farms classified as Positive stable after the first 4 consecutive samplings Positive stable farm throughout the whole study period Positive stable farms achieving second time stability after an instability period. b Farms classified as Positive unstable after the first 4 consecutive samplings Farms never reached PS. a & b Summary of PRRSV RT-PCR results, and breeding herd PRRS status classification between February 2017 and March 2018. Farms are displayed in rows and study weeks in columns. Cell codes: x/5: PCR positive pools/5 tested pools; T: negative PCR test and positive unstable status; T*: negative PCR test and positive stable status; SMV: Sows mass vaccination. Red cells: most recent testing PCR-positive; Green cells: most recent testing PCR-negative