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

Table 2 Univariable associations ^a between the weekly probability of PRRSV PCR 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			1.08	1.02 - 1.14	0.01
PRRSV outbreak^c			2.41	2.22 - 2.62	<0.001
Season^c	Fall	91	Referent	-	-
Season^c	Spring	101	1.12	1.04 - 1.22	0.005
	Summer	91	0.76	0.69 - 0.84	<0.001
	Winter	99	1.05	0.97 - 1.14	0.22
Year	2000	52	Referent	-	-
	2001	52	0.79	0.63 - 0.99	0.04
	2002	52	1.05	0.84 - 1.31	0.68
	2003	52	0.99	0.81 - 1.22	0.93
	2004	52	1.79	1.50 - 2.15	<0.001
	2005	52	1.14	0.97 - 1.35	0.11
	2006	52	0.57	0.48 - 0.67	<0.001
	2007	18	0.88	0.73 - 1.05	0.14

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

ISSN: 1746-6148