Table 6.
Analyses of relationships between dogs being Rickettsia spp. seropositive and potential risk factors stratified by age during a survey for proposed risk factors for brown dog tick infestation and Rocky Mountain spotted fever in Tijuana, México
| Univariable Predictors | Juvenile Dogs | Adult Dogs | ||||||
|---|---|---|---|---|---|---|---|---|
| No. (%) Testing Seropositive/Total | OR or t-Test | 95% CI | P-Value | No. (%) Testing Seropositive/Total | OR | 95% CI | P-Value | |
| Univariable models | ||||||||
| House variables | ||||||||
| Case/control | ||||||||
| Case | 3/6 (50.0) | 1.94 | 0.20–19.46 | 0.64 | 32/35 (91.4) | 2.81 | 0.68–11.60 | 0.15 |
| Control | 6/18 (33.3) | Reference | – | – | 77/96 (80.2) | Reference | – | – |
| Marginalization | ||||||||
| Medium | 3/7 (42.9) | Reference | – | – | 37/45 (82.2) | Reference | – | – |
| High | 3/13 (23.1) | 0.42 | 0.04–2.55 | 0.61 | 44/56 (78.6) | 0.78 | 0.26–2.34 | 0.65 |
| Very high | 3/4 (75.0) | 3.52 | 0.17–260.91 | 0.55 | 28/30 (93.3) | 3.18 | 0.56–18.03 | 0.19 |
| Debris | ||||||||
| None | 2/5 (40.0) | Reference | – | – | 24/29 (82.8) | Reference | – | – |
| A little | 4/11 (36.4) | 0.87 | 0.06–14.66 | 1 | 53/65 (81.5) | 0.9 | 0.26–3.06 | 0.86 |
| A lot | 2/7 (28.6) | 0.63 | 0.03–13.19 | 1 | 28/31 (90.3) | 1.89 | 0.37–9.62 | 0.44 |
| On a hill | ||||||||
| No | 4/9 (44.4) | Reference | – | – | 51/64 (79.7) | Reference | – | – |
| Yes | 5/15 (33.3) | 0.64 | 0.09–4.78 | 0.68 | 56/65 (86.2) | 1.68 | 0.59–4.78 | 0.33 |
| On a dirt road | ||||||||
| No | 2/7 (28.6) | Reference | – | – | 39/46 (84.8) | Reference | – | – |
| Yes | 7/17 (41.2) | 1.71 | 0.20–22.94 | 0.67 | 70/85 (82.4) | 0.86 | 0.28–2.63 | 0.79 |
| Near a canal | ||||||||
| No | 9/23 (39.1) | Reference | – | – | 92/111 (82.9) | Reference | – | – |
| Yes | 0/1 (0) | 0 | 0–64.94 | 1 | 15/18 (83.3) | 1.05 | 0.22–5.02 | 0.95 |
| Cement | – | t(10) = −1.29 | – | 0.23 | – | 1.01 | 0.99–1.02 | 0.38 |
| Mean ± SD among IFA-pos | 49.00 ± 48.87 | – | – | – | 35.47 ± 42.22 | – | – | – |
| Mean ± SD among IFA-neg | 21.67 ± 40.69 | – | – | – | 26.5 ± 35.02 | – | – | – |
| No. of ticks seen at house | t(6) = −0.92 | – | 0.39 | – | 1.02 | 0.91–1.16 | 0.69 | |
| Mean ± SD among IFA-pos | 4.57 ± 2.33 | – | – | – | 2.37 ± 6.60 | – | – | – |
| Mean ± SD among IFA-neg | 0.67 ± 1.41 | – | – | – | 1.25 ± 3.19 | – | – | – |
| No. of dogs living at house | t(17) = 0.07 | – | 0.95 | – | 1.32 | 0.97–1.78 | 0.07 | |
| Mean ± SD among IFA-pos | 2.56 ± 1.59 | – | – | – | 3.44 ± 2.39 | – | – | – |
| Mean ± SD among IFA-neg | 2.60 ± 1.55 | – | – | – | 2.46 ± 1.47 | – | – | – |
| Total No. of dogs seen | t(12) = 0.41 | – | 0.69 | 1.5 | 1.11–2.02 | 0.008 | ||
| Mean ± SD among IFA-pos | 3.78 ± 2.33 | – | – | – | 4.89 ± 3.11 | – | – | – |
| Mean ± SD among IFA-neg | 4.13 ± 1.41 | – | – | – | 3.09 ± 1.34 | – | – | – |
| Some dogs at the house allowed to go inside | ||||||||
| No | 5/14 (35.7) | Reference | – | – | 51/65 (78.5) | Reference | – | – |
| Yes | 4/10 (40.0) | 1.19 | 0.16–8.5 | 1 | 58/66 (87.9) | 2.06 | 0.75–5.71 | 0.16 |
| House infested with ticks (self-reported) | ||||||||
| No | 6/15 (40.0) | Reference | – | – | 60/72 (83.3) | Reference | – | – |
| Yes | 3/9 (33.3) | 0.76 | 0.09–5.53 | 1 | 49/59 (83.1) | 0.95 | 0.35–2.6 | 0.93 |
| Frequency of treating house with acaricide | ||||||||
| Rare to never | 5/10 (50.0) | Reference | – | – | 24/30 (80.0) | Reference | – | – |
| Once or twice/year | 3/9 (33.3) | 0.36 | 0.01–6.48 | 0.58 | 52/64 (81.0) | 1.07 | 0.33–3.45 | 0.91 |
| Multiple times/year | 1/4 (25.0) | 0.52 | 0.05–4.43 | 0.65 | 29/33 (88.0) | 1.75 | 0.41–7.49 | 0.45 |
| Frequency of treating dogs with acaricide | ||||||||
| Rare to never | 2/6 (33.3) | Reference | – | – | 18/24 (75.0) | Reference | – | – |
| Once or twice/year | 1/5 (20.0) | 0.53 | 0.01–14.52 | 1 | 42/54 (78.0) | 1.19 | 0.35–4.03 | 0.77 |
| Multiple times/year | 5/10 (50.0) | 1.92 | 0.17–30.82 | 0.63 | 40/44 (91.0) | 3.45 | 0.79–15.04 | 0.10 |
| Dog variables | ||||||||
| Allowed to roam | ||||||||
| No | 4/16 (25.0) | Reference | – | 49/61 (80.3) | Reference | – | – | |
| Yes | 4/7 (57.1) | 3.74 | 0.43–38.72 | 0.18 | 54/59 (91.5) | 2.86 | 0.84–9.67 | 0.09 |
| Body mass (kg) | ||||||||
| <10 | 3/12 (25.0) | Reference | – | – | 47/57 (82.5) | Reference | – | – |
| 10–20 | 3/8 (37.5) | 1.75 | 0.17–18.79 | 0.64 | 36/44 (81.8) | 1.02 | 0.34–3.02 | 0.98 |
| >20 | 3/4 (75.0) | 7.64 | 0.43–521.09 | 0.12 | 25/29 (86.2) | 1.37 | 0.36–5.16 | 0.64 |
| Sex | ||||||||
| Female | 4/12 (33.3) | Reference | – | – | 56/66 (84.9) | Reference | – | – |
| Male | 5/12 (41.7) | 1.41 | 0.20–10.36 | 1 | 52/64 (81.3) | 0.75 | 0.28–1.97 | 0.56 |
| Ticks on dog | ||||||||
| No ticks | 4/10 (40.0) | Reference | – | – | 35/45 (77.8) | Reference | – | – |
| 1–10 ticks | – | – | – | – | 37/47 (78.7) | 1.1 | 0.38–3.17 | 0.86 |
| >10 ticks (any ticks present, juvenile) | 5/13 (38.5) | 0.94 | 0.13–7.06 | 1 | 35/37 (94.6) | 5.48 | 1.04–28.93 | 0.05 |
| Body condition | ||||||||
| Normal (2–3) | 7/21 (33.3) | Reference | – | – | 82/104 (78.9) | – | – | – |
| Unhealthy (<2 or >3) | 2/3 (66.7) | 3.76 | 0.17–251.98 | 0.53 | 24/24 (100) | – | – | – |
| Multivariable Models (adults only) | ||||||||
|---|---|---|---|---|---|---|---|---|
| Multivariable predictors | Predictor | OR | 95% CI | P-Value | – | – | – | – |
| Model 1 | (Intercept) | 0.85 | 0.26–2.70 | 0.78 | – | – | – | – |
| Total No. of dogs seen | 1.50 | 1.10–2.05 | 0.01 | – | – | – | – | |
| Ticks on dog (>10) | 4.52 | 0.90–22.82 | 0.07 | – | – | – | – | |
| Model 2 | (Intercept) | 0.97 | 0.26–3.68 | 0.96 | – | – | – | – |
| Total No. of dogs seen | 1.44 | 1.03–2.01 | 0.03 | – | – | – | – | |
| Ticks on dog (>10) | 2.75 | 0.53–14.43 | 0.23 | – | – | – | – | |
| Dog allowed to roam (yes) | 2.10 | 0.59–7.57 | 0.25 | – | – | – | – | |
IFA-neg = immunofluorescence antibody assay–negative; IFA-pos = immunofluorescence antibody assay–positive; OR = odds ratio.