Assessment of exposure to influenza A viruses in pigs between weaning and market age

Table 2 Incidence and prevalence in the nursery and finisher phase in Study 1 and frequency table indicating percentage of pigs with a distinct change in the serological status at the end of each production phase

Phase of production and categories		%
Phase of production and categories		H3N2_A^*	H3N2_B^*	H3N2_C^*	H3N2_H^†	H1N2^‡	H1N1_P^¶	H1N1_C^§	H1N1_H^†
Nursery	Incidence^** (%) (95% CI)	96 (0.89, 0.99)	93 (0.78, 0.99)	55 (0.38, 0.70)	95 (0.76, 0.99)	0 –	0 –	4 (0.01, 0.11)	48 (0.32, 0.65)
	Prevalence (%) (95% CI)	97 (0.91, 0.99)	88 (0.79, 0.94)	53 (0.41, 0.64)	79 (0.69, 0.87)	0 –	1 (0.01, 0.06)	3 (0.01, 0.10)	49 (0.37, 0.60)
	Proportion of study animals in strata defined by the serological exposure status at the start and end of study period
	N–N¹	2.4	2.4	22.0	1.2	43.9	78.1	84.2	24.4
	N–P^2*&	75.6	35.4	26.8	24.4	0.0	0.0	3.7	23.2
	P–N³	0.0	8.5	23.2	18.3	52.4	17.1	8.5	24.4
	P–P^4*	18.3	50.0	24.4	52.4	0.0	1.2	0.0	24.4
Finisher	Incidence (%) (95% CI)	–	–	0 –	0 –	1 (0.01, 0.09)	0 –	0 –	0 –
	Prevalence (%) (95% CI)	61 (0.47, 0.74)	91 (0.80, 0.97)	1 (0.01, 0.09)	19 (0.10, 0.31)	1 (0.01, 0.09)	0 –	0 –	0 –
	Proportion of study animals in strata defined by the serological exposure status at the start and end of study period
	N–N	0.0	0.0	32.9	15.9	67.1	67.1	65.9	35.4
	N–P	1.2	9.8	0.0	0.0	1.2	0.0	0.0	0.0
	P–N	26.8	6.1	34.2	37.8	0.0	1.2	2.4	32.9
	P–P	40.2	52.4	1.2	14.6	0 (0)	0.0	0.0	0.0

^*Different H3N2 variants broadly classified into cluster 4 of H3N2 swine influenza A virus and isolated in Ontario in 2012 and used in the hemagglutination inhibition assay.
^†H3N2 and H1N1 viruses detected in the study and used as antigens in the hemagglutination inhibition assay.
^‡H1N2 with hemagglutinin of the 2009 pandemic lineage and neuraminidase of the Cluster 4 H3N2 IAV-S.
^§H1N1 IAV-S broadly classified as the classical swine H1N1 virus used in the hemagglutination inhibition assay.
^¶H1N1 IAV-S of the 2009 H1N1 pandemic lineage used in the hemagglutination inhibition assay.
¹Negative titers in both measurements.
^2*&Negative titers in the measurement at the end of nursery and positive titers at the end of finisher. Used to calculate prevalence ^* and incidence risk^&.
³Positive titers in the measurement at the end of nursery and negative titers at the end of finisher.
^4*Positive titers in the measurement at the end of nursery and positive titers at the end of finisher. Used to calculate prevalence.
^**Incidence was only calculated if more than three pigs were positive.
Total number of pigs at the end of nursery and end of finisher periods were 79 and 56, respectively. Pigs that died during the trial were treated as missing values.

ISSN: 1297-9716