Comparison of serological assays for detecting antibodies in ducks exposed to H5 subtype avian influenza virus

BMC Veterinary Research

Table 1 Number and proportion of serum samples testing H5 antibody positive in three serological tests in ducks experimentally infected with H5N1

Test results	Pre-inoculation	8 dpi	15 dpi	22 dpi	29 dpi	34 dpi	Overall
N HI-CRBC pos	0	4	8	8	7	7	34
Prop HI-CRBC pos	0	0.4	0.8	0.8	0.7	0.7	0.57
(95%-CI)^1,2	(0–0.31)	(0.12-0.74)	(0.44-0.98)	(0.44-0.98)	(0.35-0.93)	(0.35-0.93)	(0.33-0.81)
N HI-HRBC pos	0	7	8	7	7	7	36
Prop HI-HRBC pos	0	0.7	0.8	0.7	0.7	0.7	0.60
(95%-CI)^1,2	(0–0.31)	(0.35-0.93)	(0.44-0.98)	(0.35-0.93)	(0.35-0.93)	(0.35-0.93)	(0.33-0.87)
N VN pos	0	2	8	8	8	9	35
Prop VN pos	0	0.2	0.8	0.8	0.8	0.9	0.58
(95%-CI)^1,2	(0–0.31)	(0.03-0.56)	(0.44-0.98)	(0.44-0.98)	(0.44-0.98)	(0.55-1.00)	(0.40-0.76)

A titre cut-off of ≥ 4 log2 (16) was used to distinguish between positive and negative results. Ten ducks were sampled before inoculation and at 8, 15, 22, 29 and 34 days after virus inoculation. Abbreviations: HI-CRBC (Haemagglutination inhibition test using chicken red blood cells), HI-HRBC (Haemagglutination inhibition test using horse red blood cells), VN (Virus neutralisation test), N (number), Prop (proportion), dpi (day post inoculation), CI (confidence interval).
¹Binominal exact confidence intervals were calculated for the proportion of positives at each sampling period.
²Confidence intervals for the overall proportion of positives were adjusted for a clustering of birds by sampling period (10 clusters).

ISSN: 1746-6148