TABLE 2.

Percentages of samples positive for Salmonella and herd sizes on 18 dairy farms sampled in the summers of 2000 or 2001 and 2009

Farm	2000-2001					2009
	Herd sizea	Prevalence				Herd size	Prevalence, summer visits
		All visits		Summer visits
		% positive	No. positive/total	% positive	No. positive/total		% positive	No. positive/total
101b	78	3.6	19/528	5.4	2/37	60	62.9	22/35
102	113	0.4	3/696	2	1/51	197	0.0	0/36
108	77	0	0/221	0	0/38	145	0.0	0/38
109	318	0	0/302	0	0/60	700	57.4	27/47
111b	108	44.9	118/263	64.2	34/53	116	6.2	5/81
112	74	1	2/194	2.9	1/34	83	0.0	0/38
114b	110	29.3	76/259	23.9	11/46	193	29.8	14/47
118	191	0	0/268	0	0/57	158	0.0	0/46
119	116	0.4	1/250	2.2	1/46	99	0.0	0/35
121b	473	0.7	2/267	1.6	1/63	818	20.0	10/50
122	186	0	0/293	0	0/57	503	8.5	4/47
125b	257	5.2	15/289	25	14/56	511	23.9	11/46
126	305	0.3	1/301	0	0/59	1,067	0.0	0/46
127	84	0.5	1/207	2.5	1/40	90	0.0	0/37
128	151	0.3	1/288	1.9	1/54	170	0.0	0/42
129b	247	6.9	22/319	18	11/61	456	2.2	2/91
131	87	1	2/201	0	0/36	63	3.2	1/31
132	90	0.5	1/212	2.4	1/42	76	2.7	1/37
Total		4.9	264/5,358	8.9	79/890		12.4	97/830

^aApproximate total number of lactating cows.

^bOne of six farms where isolates were selected for additional characterization.