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Table 4 The association a between the weekly probability of PRRSV PCR 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   0.66 0.58 - 0 .75 0.01
PRRSV outbreak c   2.53 2.14 - 2.97 <0.001
Seasonc Fall 91 Referent -  
Spring 101 0.92 0.60 - 1.43 0.72
  Summer 91 0.57 0.35 - 0.93 0.02
Winter 99 0.85 0.55 - 1.33 0.49
Year 2000 52 Referent - -
2001 52 0.81 0.51 - 1.30 0.38
2002 52 0.95 0.60 - 1.52 0.84
2003 52 0.90 0.60 - 1.35 0.61
2004 52 0.66 0.44 - 0.99 0.04
2005 52 1.04 0.71 - 1.50 0.85
2006 52 0.49 0.35 - 0.70 <0.001
  2007 18 0.85 0.62 - 1.17 0.32
Year*Season interactiond 2001*spring   0.58 0.30 - 1.12 0.11
2001*summer   2.98 1.51 - 5.86 0.002
2001*winter   0.66 0.35 - 1.25 0.20
2002*spring   0.95 0.51 - 1.76 0.86
2002*summer   0.97 0.46 - 2.01 0.93
2002*winter   1.34 0.72 - 2.49 0.35
2003*spring   0.77 0.44 - 1.36 0.37
2003*summer   0.66 0.34 - 1.31 0.23
2003*winter   2.06 1.18 - 3.06 0.01
2004*spring   0.85 0.51 - 1.40 0.52
2004*summer   1.22 0.69 - 2.17 0.49
2004*winter   2.24 1.34 - 3.74 0.002
2005*spring   2.19 1.39 - 3.47 0.001
2005*summer   2.06 1.23 - 3.48 0.006
2005*winter   0.98 0.61 - 1.59 0.94
2006*spring   1.61 1.01 - 2.57 0.045
2006*summer   1.09 0.65 - 1.85 0.74
2006*winter   1.57 0.97 - 2.54 0.07
  2007*spring   0.93 0.59 - 1.45 0.74
  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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