Table 2. Swine and human influenza viruses: HI antigenic characterization of H1 strains.

		HI titer of serum against:
Virus origin	Virus strain	A/Sw/It/114347–1/06 (H1N2)*	A/Sw/It/125746/05 (H1N1)*	A/Brisbane/59/07 (H1N1)*	A/California/7/09 (H1N1)**
Swine	A/Sw/It/114347-1/06, H1N2 ∧	80	<10	<10	<10
Swine	A/Sw/It/125746/05, H1N1	<10	1280	10	80
	A/Sw/It/66732/2/06, H1N1∧	<10	1280	<10	320
	A/Sw/It/87491/06, H1N1∧	<10	1280	<10	160
	A/Sw/It/45894/2/07, H1N1∧	<10	640	<10	160
	A/Sw/It/68030/07, H1N1∧	<10	640	<10	160
	A/Sw/It/232868/07, H1N1∧	<10	1280	<10	320
	A/Sw/It/207871/08, H1N1∧	<10	640	<10	160
	A/Sw/It/44795/08, H1N1 ∧	<10	640	<10	160
Human	A/Brisbane/59/07, H1N1	10	20	1280	<10
	A/California/7/09, H1N1	<10	160	<10	1280

HI, Haemagglutination inhibition.

^*Chicken hyperimmune antiserum.

^**Ferret post-infection antiserum.

Virus strains used to test swine workers’ and controls’ sera are underlined.

^∧SIVs strains isolated from pigs, in the farms under study.