Active disease finding: sampling and testing for HPAI
Tables 3 and 4 and Figure 5 show the numbers of pooled samples tested for AIV, H5 and H9, as well as their results. Proportionally, most AIV was found in LBMs (45 out of 249 samples tested, 18.1%). Similar quantities were found in collector yards (73 out of 607 samples), nomadic duck flocks (118 out of 904 samples) and backyard poultry (19 out of 146); all prevalences range from 12 to 13%. However, significantly more H5 viruses were found in LBMs and collector yards (13 out of 249 samples, 5.2% and 29 out of 607 samples, 4.8%, respectively). The pattern of H9 was somewhat different, with 19 out of 249 (7.6%) of samples from LBMs testing positive; similar quantities were detected in collector yards and backyard poultry (23 out of 607 samples, 3.8% and 5 out of 146 samples, 3.4%). While the prevalence of AIV was lower in Sector 3 commercial poultry, one sample tested positive for H5. About half of the AIV detected in commercial poultry were H9, the other half being non-H5, non-H9 AIV.
Overall, H9 were identified in 10/41 collector yards (25%), 10/18 LBMs (55%) and 5/31 commercial farms (16%) over the duration of the study. A number of collector yards as well as LBMs repeatedly tested positive. One LBM in particular (M-12) was positive at every sampling. No commercial farm tested positive more than once; however, these farms were only sampled half as frequently. As the sampling no or limited repeat sampling was carried out in backyard and nomadic duck flocks, we were unable to assess this in these sectors.
Table 5 shows the pairwise statistical tests for significant differences between enterprise types of detection of H5. The odds ratio between LBMs and collector yards was about 1 and the difference was not statistically significant. However, the odds between both of these enterprise types and commercial farms was in the order of 25 to 30 (and highly significant); nomadic duck flocks, 3.5 to 4 (and highly significant); and backyard poultry, 3.5 to 4 (and marginally significant). Both nomadic duck flocks and backyard poultry had approximately 7 times higher odds than commercial farms, but the association between backyard poultry and commercial farms was not significant, probably due to the small numbers of detections.