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Table 3 The association a between the weekly probability of PRRSV ELISA positivity and the PCVAD outbreak of the Ontario swine industry after controlling for a PRRSV outbreak, season and year using data from the Animal Health Laboratory from January 2000 and April 2007

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

Variable n ORb 95% CI P-value
PCVAD outbreak   1.33 0.97 - 1.83 0.08
PRRSV outbreakc   0.83 0.56 - 1.24 0.36
Seasonc Fall 91 Referent - -
Spring 101 0.86 0.56 - 1.28 0.43
  Summer 91 1.01 0.66 - 1.54 0.98
Winter 99 1.12 0.73 - 1.72 0.62
Year 2000 52 Referent - -
2001 52 0.92 0.61 - 1.38 0.68
2002 52 1.06 0.72 - 1.57 0.76
2003 52 0.66 0.44 - 0.99 0.047
2004 52 0.86 0.49 - 1.50 0.59
2005 52 0.36 0.22 - 0.59 <0.001
2006 52 0.22 0.15 - 0.34 <0.001
2007 18 0.22 0.15 - 0.34 <0.001
Year*Season interactiond 2001*spring 0.84 1.15 0.64 - 2.07 0.64
2001*summer 0.88 0.58 0.46 - 1.54 0.58
2001*winter 1.10 0.66 0.49 - 1.58 0.66
2002*spring 0.89 0.73 0.63 - 1.92 0.73
2002*summer 0.69 0.69 0.51 - 1.57 0.69
2002*winter 1.17 0.19 0.39 - 1.21 0.19
2003*spring 1.13 0.58 0.67 - 2.05 0.58
2003*summer 1.32 0.68 0.63 - 2.04 0.68
2003*winter 1.65 0.33 0.75 - 2.33 0.33
2004*spring 0.88 0.08 0.95 - 2.87 0.08
2004*summer 0.76 0.65 0.50 - 1.55 0.65
2004*winter 1.70 0.41 0.40 - 1.45 0.41
2005*spring 1.09 0.05 0.99 - 2.90 0.05
2005*summer 1.46 0.75 0.63 - 1.90 0.75
2005*winter 2.24 0.23 0.79 - 2.72 0.23
2006*spring 1.50 0.007 1.25 - 4.00 0.007
2006*summer 1.25 0.16 0.86 - 2.63 0.16
2006*winter 1.26 0.47 0.69 - 2.26 0.47
  2007*spring 0.84 0.42 0.69 - 2.31 0.42
  1. 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.
  2. b. Odds ratio.
  3. c. Suspected a priori may be a confounding variable.
  4. d. Interaction term.
  5. bold text – significant variables.
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