Table 4. Multivariate logistic regression model to identify variables associated with a positive real-time RT-PCR result, Texas mid–Gulf Coast, USA, 2006–07, 2007–08, and 2008–09*.

Variable	Odds ratio (95% CI)	p value
Sex
Drake	1.0†
Hen	1.07 (0.859–1.320)	0.558
Age
Adult	1.0
Juvenile	1.45 (1.17–1.81)	0.001
Species
Other species	1.0
Gadwall	0.407 (0.120–0.825)	0.013
Northern shoveler	1.51 (0.987–2.320)	0.057
Blue-winged teal	2.18 (1.52–3.13)	<0.001
Green-winged teal	1.12 (0.742–1.680)	0.592

*Results for a total of 4,187 samples, collected during September–January for each season. RT-PCR, reverse transcription–PCR; CI, confidence interval. Boldface indicates significant result.
†Reference category.