Epidemiological surveillance and economic impact analysis of different porcine reproductive and respiratory syndrome virus infection statuses in 23 breeding pig farms in Hubei, China

Table 8 The modified classification system of different PRRSV infection status in pig farms

Farm type	Monthly monitoring result of PRRSV antigen and antibody	PRRSV infection status
Not using PRRSV vaccine	PRRSV antigen positivity (at least one positive sample) or an antibody positive rate > 50%	PRRSV-positive unstable
	The PRRSV antigen is negative and the antibody positive rate is between 0 and 50%	PRRSV-positive stable
	The PRRSV antigen and antibody results are both negative for three consecutive months or more,	PRRSV provisional negative
Using PRRSV vaccine	PRRSV antigen positivity (at least one positive sample)	PRRSV-positive unstable
Using PRRSV vaccine	PRRSV antigen negativity	PRRSV-positive stable