Table 3. Univariable mixed effects logistic regression analysis of risk factors associated with Rift Valley fever seropositivity in domestic ruminants (herd was included as random effect variable).
| Variable | No. tested | No. seropositive (%) | OR | 95% CI | z value | p value | * Pearson Chi square | *DF | *p value |
|---|---|---|---|---|---|---|---|---|---|
| Rift Valley ecosystem | |||||||||
| Study villages in the western Rift Valley ecosystem | 691 | 136 | 1.0 | Ref. | Ref. | Ref. | Ref. | ||
| Study villages in the eastern Rift Valley ecosystem | 744 | 234 | 1.88 | 1.41, 2.51 | 4.29 | < 0.001 | 18.42 | 1 | <0.0001 |
| Village | |||||||||
| Bukirilo | 233 | 36 (15.5) | 1.00 | Ref. | Ref. | Ref. | |||
| Chamae | 244 | 92 (37.7) | 3.32 | 2.13, 5.17 | 5.29 | < 0.001 | |||
| Malambo | 243 | 92 (37.9) | 3.33 | 2.15, 5.19 | 5.31 | < 0.001 | |||
| Kajunjumele | 225 | 58 (25.8) | 1.9 | 1.19, 3.04 | 2.69 | 0.007 | |||
| Ninchoka | 257 | 50 (19.5) | 1.32 | 0.83, 2.13 | 1.15 | 0.249 | |||
| Nyakasimbi | 233 | 42 (18.0) | 1.2 | 0.74, 1.96 | 0.73 | 0.463 | 58.83 | 5 | < 0.001 |
| Rainfall pattern in the study areas | |||||||||
| Unimodal | 702 | 186 (26.5) | 1.00 | Ref. | Ref. | Ref. | |||
| Bimodal | 733 | 184 (25.1) | 0.91 | 0.67–1.24 | -0.60 | 0.551 | 0.36 | 1 | 0.551 |
| Average total annual rainfall (mm) in the study areas | |||||||||
| ≤712 | 487 | 184 (37.7) | 1.00 | Ref. | Ref. | Ref. | |||
| >712–966 | 490 | 92 (18.8) | 0.38 | 0.28, 0.51 | -6.26 | <0.001 | |||
| >966 | 458 | 94 (20.5) | 0.43 | 0.31, 0.58 | -5.53 | <0.001 | 49.97 | 2 | <0.001 |
| Average monthly rainfall (mm) in the study areas | |||||||||
| ≤47 | 487 | 184 (37.8) | 1.00 | Ref. | Ref. | Ref. | |||
| >47–74 | 490 | 87 (17.6) | 0.35 | 0.26, 0.47 | -6.76 | < 0.001 | |||
| >74 | 458 | 100 (21.8) | 0.46 | 0.34, 0.62 | -5.15 | < 0.001 | 52.87 | 2 | < 0.001 |
| Water holding capacity of soils in the study areas | |||||||||
| Poor | 466 | 78 (16.7) | 1.00 | Ref. | Ref. | Ref. | |||
| Good | 969 | 292 (30.1) | 2.18 | 1.58, 3.02 | 4.73 | < 0.001 | 22.36 | 1 | < 0.001 |
| Species | |||||||||
| Caprine | 531 | 116 (21.9) | 1.00 | Ref. | Ref. | Ref. | |||
| Ovine | 148 | 44 (29.7) | 1.51 | 0.96, 2.38 | 1.78 | 0.075 | |||
| Bovine | 756 | 210 (27.8) | 1.39 | 1.01, 1.91 | 2.02 | 0.044 | 5.32 | 2 | 0.071 |
| Sex | |||||||||
| Male | 299 | 64 (21.4) | 1.00 | Ref. | Ref. | Ref. | |||
| Female | 1136 | 306 (26.9) | 1.44 | 1.04, 1.99 | 2.22 | 0.026 | 4.93 | 1 | 0.026 |
| Breed | |||||||||
| Indigenous | 1374 | 342 (24.9) | 1.00 | Ref. | Ref. | Ref. | |||
| Cross breed | 61 | 28 (45.9) | 2.67 | 1.51, 4.70 | 3.39 | 0.001 | 11.49 | 1 | 0.0007 |
| Age (years) | |||||||||
| 1–2 | 599 | 85 (14.2) | 1.00 | Ref. | Ref. | Ref. | |||
| 3 | 578 | 198 (34.3) | 3.4 | 2.49, 4.64 | 7.73 | < 0.001 | |||
| 4–5 | 258 | 87 (33.7) | 3.31 | 2.27, 4.82 | 6.25 | < 0.001 | 65.91 | 2 | < 0.001 |
| Animals with history of abortion | |||||||||
| No | 870 | 226 (26.0) | 1.00 | Ref. | Ref. | Ref. | |||
| Yes | 12 | 7 (58.3) | 4.13 | 1.19, 14.41 | 2.23 | 0.026 | 4.96 | 1 | 0.026 |
| Animal source | |||||||||
| Born within herd | 1383 | 339 (24.5) | 1.00 | Ref. | Ref. | Ref. | |||
| Introduced into the herd | 52 | 31 (59.6) | 5.08 | 2.74, 9.44 | 5.15 | < 0.001 | 26.51 | 1 | < 0.001 |
| Animal sampled from district with history of RVF outbreaks | |||||||||
| No | 691 | 136 (19.7) | 1.00 | Ref. | Ref. | Ref. | |||
| Yes | 744 | 234 (31.5) | 1.88 | 1.41, 2.51 | 4.29 | < 0.001 | 18.42 | 1 | < 0.001 |
| Animal with diarrhoea | |||||||||
| No | 1372 | 353 (25.7) | 1.00 | Ref. | Ref. | Ref. | |||
| Yes | 63 | 17 (27.0) | 0.94 | 0.45–1.96 | -0.15 | 0.878 | 0.02 | 1 | 0.878 |
| Animal with nasal discharge | |||||||||
| No | 1418 | 366 (25.8) | 1.00 | Ref. | Ref. | Ref. | |||
| Yes | 17 | 4 (23.5) | 1.12 | 0.35–3.66 | 0.19 | 0.846 | 0.04 | 1 | 0.846 |
| Cattle density (heads per square km) | |||||||||
| ≤19 | 691 | 126 (19.7) | 1.00 | Ref. | Ref. | Ref. | |||
| >19–30 | 500 | 142 (28.4) | 1.61 | 1.18–2.21 | 2.96 | 0.003 | |||
| >30 | 244 | 92 (37.7) | 2.52 | 1.72–3.68 | 4.77 | < 0.001 | 24.31 | 2 | < 0.001 |
| Goats density (heads per square km) | |||||||||
| ≤14 | 715 | 144 (20.1) | 1.00 | Ref. | Ref. | Ref. | |||
| >14–25 | 477 | 134 (28.1) | 1.54 | 1.13–2.11 | 2.72 | 0.007 | |||
| >25 | 243 | 92 (38.9) | 2.36 | 1.63–3.42 | 4.53 | < 0.001 | 21.83 | 2 | < 0.001 |
| Sheep density (heads per square km) | |||||||||
| ≤2 | 691 | 136 (19.7) | 1.00 | Ref. | Ref. | Ref. | |||
| >2–8 | 501 | 142 (28.3) | 1.64 | 1.20–2.23 | 3.10 | 0.002 | |||
| >8 | 243 | 92 (37.9) | 2.44 | 1.68–3.55 | 4.69 | < 0.001 | 24.05 | 2 | < 0.001 |
| Feeding practices | |||||||||
| grazing only | 1210 | 312 (25.8) | 1.00 | Ref. | Ref. | Ref. | |||
| stall-feeding combined with grazing | 225 | 58 (25.8) | 1.04 | 0.68–1.57 | 0.17 | 0.865 | 0.03 | 1 | 0.865 |
OR, odds ratio; CI, confidence interval; Ref, reference group; SE, Standard error; DE, Degrees of freedom
* The effect of potential risk factors in the univariable mixed-effects logistic regression model