Table 2.
Rate and Relative Risk (RR), with accompanying 95% confidence interval, of introduction of a Low pathogenic avian influenza virus infection onto poultry farms. Indoor‐layer farms were considered as the reference category
| Poultry type | Rate/month* | RR** | ||||
|---|---|---|---|---|---|---|
| Mean | LCL*** | UCL*** | Mean | LCL | UCL | |
| Broiler breeders | 1·0 × 10−4 | 1·4 × 10−5 | 7·8 × 10−4 | 0·3 | 0·0 | 2·4 |
| Pullets | 2·5 × 10−4 | 3·2 × 10−5 | 1·9 × 10−3 | 0·7 | 0·1 | 5·7 |
| Indoor‐layers | 3·5 × 10−4 | 1·5 × 10−4 | 8·1 × 10−4 | 1·0 | ||
| Outdoor‐layers | 3·9 × 10−3 | 2·1 × 10−3 | 7·4 × 10−3 | 11·1 | 4·9 | 25·2 |
| Turkeys | 2·7 × 10−3 | 7·9 × 10−4 | 9·3 × 10−3 | 7·7 | 2·0 | 29·3 |
| Duck meat | 4·5 × 10−3 | 5·9 × 10−4 | 3·4 × 10−2 | 12·8 | 1·6 | 103·6 |
| Duck breeders | 8·6 × 10−3 | 2·5 × 10−3 | 3·0 × 10−2 | 24·5 | 6·4 | 94·1 |
| Broilers† | 0·0 | 0·0 | 8·1 × 10−4 | 0·0 | ||
*Limits of the confidence interval. Lower confidence limit (LCL) and upper confidence limit (UCL).
**The exponent of the model intercept β0 is the rate of introduction onto Indoor‐layers. This rate for a different PT, say Broiler breeders = exp(β0 + βbreeders) and the variance (var) = exp [var (β0) + var (βbreeders) + 2cov (β0βbreeders)]. Confidence intervals were estimated using the normal approximation = mean ± 1·96*sqrt (var).
***The RR was obtained by exponentiation of the model parameters. E.g. the RR for breeders = exp (βbreeders). Confidence intervals were obtained by the normal approximation using the estimated variance of βbreeders.
†One‐sided 95% confidence interval of the rate of introduction per month were estimated. Here the number of farms (samplings) times the months at risk (3719 farm‐months at risk) in the study period (2007–July 2010) was taken as the denominator.