Identifying an outbreak of a novel swine disease using test requests for porcine reproductive and respiratory syndrome as a syndromic surveillance tool

Table 1 Univariable associations ^a between the weekly probability of PRRSV ELISA positivity at the Animal Health Laboratory from January 1, 2000 to April 30, 2007 and the PCVAD outbreak of the Ontario swine industry, a PRRSV outbreak, season, and year

Variable		n	OR^b	95% CI	P-value
PCVAD outbreak			0.87	0.77 - 0.97	0.02
PRRSV outbreak^c			1.19	1.04 - 1.37	0.01
Season^c	Fall	91	Referent	-	-
Season^c	Spring	101	1.08	0.95 - 1.24	0.25
	Summer	91	1.05	0.91 - 1.21	0.50
	Winter	99	1.05	0.92 - 1.20	0.77
Year	2000	-	Referent	-	-
	2001	52	0.89	0.72 - 1.10	0.28
	2002	52	0.97	0.79 - 1.18	0.75
	2003	52	0.77	0.63 - 0.94	0.01
	2004	52	0.78	0.64 - 0.95	0.01
	2005	52	0.60	0.49 - 0.73	<0.001
	2006	52	0.37	0.31 - 0.45	<0.001
	2007	18	0.25	0.19 - 0.32	<0.001

a. Logistic regression using generalized linear model ML estimation with the logit link, binomial distribution and total number of PRRSV ELISA tests ordered representing the denominator.
b. Odds ratio.
c. Suspected a priori may be a confounding variable.

ISSN: 1746-6148