Table 3.

Seroprevalence in farms according to the herd size

Herd size	Seroprevalence (95% IC)	OR (95% IC)	P
<1000	51.2% (45.8–56.8)	1.1 (0.8–1.4)	0.70
1000–4000	40.7% (37.4–44.1)	0.4 (0.3–0.5)	<0.0001
>4000	75.1% (70.2–80)	3.9 (2.9–5.2)	<0.0001