Table 1.

Univariate associations of potential risk factors with seropositivity to Rift Valley fever virus in cattle, sheep and goats in central South Africa, 2015–2016.

Variable and level	Number of animals sampled	Number testing positive	% seropositive	P-value†
District*				<0.001
(19 districts)	3,049	622	20.4
Year sampled*				0.019
2015	2773	550	19.8
2016	276	72	26.1
Species*				<0.001
Cattle	977	311	31.8
Sheep	1549	255	16.5
Goats	523	56	10.7
Breed*				<0.001
Indigenous	1132	153	13.5
Exotic	1043	258	24.7
Cross	585	163	27.9
Age*				<0.001
<2y	929	40	4.3
2–4y	811	97	12.0
>4y	1294	484	37.4
Sex*				<0.001
Female	2704	590	21.8
Male	343	32	9.3
Animal born on farm*				0.142
No	464	104	22.4
Yes	2262	438	19.4
Animal vaccinated against RVF*				<0.001
No	1892	278	14.7
Yes	626	226	36.1
Unknown	531	118	22.2
Type of farm*				0.001
Communal	308	17	5.5
Private	2729	604	22.1
Production system*				<0.001
Commercial	1790	436	24.4
Semi-commercial	733	115	15.7
Feedlot	202	53	26.2
Communal	308	17	5.5
Main industry*				0.001
Meat	1711	361	21.1
Wool	663	147	22.2
Dairy	62	28	45.2
Other	289	68	23.5
Animals mix with other domestic ruminants				0.279
No	1647	349	21.2
Yes	1389	274	19.6
Animals mix with wildlife*				0.001
No	1592	290	18.2
Yes	1444	331	22.9
Animals kraaled at night*				<0.001
No	2232	511	22.9
Yes	751	97	12.9
Contact with animals on another farm				0.699
No	2402	495	20.6
Yes	635	126	19.8
Animals have access to perennial spring, lake or pond				0.263
No	1836	363	19.8
Yes	1150	247	21.5
Animals have access to perennial river or stream*				0.011
No	1992	380	19.1
Yes	994	230	23.1
Animals have access to seasonal pan*				<0.001
No	1923	338	17.6
Yes	1063	272	25.6
Animals have access to manmade water source (dam)				0.405
No	761	147	19.3
Yes	2225	463	20.8
New cattle brought onto farm in past 12 months*				<0.001
No	1956	362	18.5
Yes	1074	259	24.1
New goats brought onto farm in past 12 months*				0.040
No	2688	565	21.0
Yes	345	56	16.2
New sheep brought onto farm in past 12 months				0.272
No	2026	403	19.9
Yes	1007	218	21.6
Quarantine practiced when introducing animals*				0.014
No	2276	442	19.4
Yes	757	179	23.6
Vehicles cleaned and disinfected before and after transporting animals*				<0.001
No	1637	290	17.7
Yes	1396	331	23.7
Mosquito or fly control practised*				0.103
No	1353	259	19.1
Yes	1680	362	21.5
Animals slaughtered on farm*				0.071
No	825	201	24.4
Yes	1900	403	21.2
Year of last RVF vaccination on farm*				0.003
Never	2018	387	19.2
2009–2011	442	90	20.4
2012–2013	263	51	19.4
2014–2016	308	90	29.2
Unknown	18	4	22.2
Farm size				0.331
<400 ha	565	108	19.1
400–1000 ha	665	133	20.0
1001–3000 ha	1021	232	22.7
>3000 ha	714	148	20.7
Total number of animals on farm*				0.001
1–100	689	103	14.9
101–300	690	145	21.0
301–1000	741	165	22.3
>1000	929	209	22.5
Any animals aborted in past 3 months**				0.001
No	2290	438	19.1
Yes	743	183	24.6
RVF ever confirmed on farm**				0.027
No	1844	386	20.9
Yes	881	218	24.7

^†P-value for Fisher’s exact test.

*Variable selected for inclusion into multiple logistic regression model (P < 0.20).

**Variable considered a consequence rather than a potential risk factor, therefore not considered for multivariable model.