Individual and environmental factors associated with the seroprevalence of Borrelia burgdorferi in Belgian farmers and veterinarians

Figures & data

Table 1 Summary statistics of environmental covariables

	Descriptive statistics
Variables	Mean	Standard deviation	Range
Landscape composition variables
Proportion of artificial lands (%)	15.2	8.9	4.7–45.3
Proportion of forest and semi-natural habitats (%)	25.0	18.9	0.2–77.3
Proportion of wetland (%)	0.3	1.5	0–9.7
Proportion of grassland (%)	31.8	15.2	9.4–74.5
Proportion of arable lands (%)	25.4	21.1	0.5–72.5
Proportion of permanent crops (%)	0.7	1.2	0–8.6
Proportion of fallow lands (%)	0.5	0.4	0.1–3.4
Landscape configuration variables
Area-weighted mean shape index (−)	1.9	0.20	1.4–2.7
Area-weighted mean patch fractal dimension (−)	1.3	0.03	1.3–1.4
Edge density (m/ha)	54.6	33.8	1.7–147.9
Patch density number (#/ha)	9.4	5.3	0.60–25.7
Edge proportion grassland – artificial land (%)	46.3	9.8	17.3–70.5
Edge proportion grassland – arable land (%)	24.4	11.4	2.0–47.2
Edge proportion grassland – agricultural building (%)	3.3	1.7	0.5–7.9
Edge proportion grassland – fallow land (%)	0.9	0.4	0.3–2.4
Edge proportion grassland – water surfaces (%)	7.2	2.6	2.5–17.7
Wildlife variables
Boars density per municipality (n/km^2)	0.8	1.2	0–7.3
Roe deer density per municipality (n/km^2)	1.4	1.8	0–7.6
Deer density per municipality (n/km^2)	0.4	0.5	0–2.3
Boars density shot per municipality (n/km^2)	0.7	1.0	0–4.8
Roe deer density shot per municipality (n/km^2)	0.7	0.8	0–3.3
Deer density shot per municipality (n/km^2)	0.2	0.2	0–1.0

Table 2 Stratified seroprevalence of Borrelia burgdorferi antibodies in veterinarians and farmers

Characteristic	No. of positive/total	Seroprevalence (%) (95% CI based on Poisson model)	OR (95% CI)
Sex
Male	7/109	6.42 (2.58–13.23)
Female	0/18	0 (0–20.5)
Occupation
Farmers	3/31	9.68 (2.00–28.29)	2.46 (0.52–11.67)
Veterinarians	4/96	4.17 (1.13–10.67)	1
Age group (years)
25–39	0/31	0 (0–11.90)
40–49	1/30	3.33 (0.08–18.57)	1
50–59	4/45	8.88 (2.42–22.75)	2.83 (0.30–26.64)
60–72	2/20	10.0 (1.21–36.1)	3.22 (0.27–38.15)
Residence municipality
Walloon Brabant	0/5	0 (0–73.8)	–
Hainaut	3/26	11.54 (2.38–33.73)	3.26 (0.32–33.61)
Liege	3/37	8.11 (1.67–23.70)	2.21 (0.22–22.47)
Luxemburg	1/26	3.85 (0.97–21.42)	1
Namur	0/33	0 (0–11.18)	–

Fig. 1 Location of participants and serological results for Borrelia burgdorferi infections.

Table 3 Multivariate logistic regression

Presence or absence of Borrelia infection	Coefficient in univariate regression	Coefficient (±SE) in multivariate regression ()
Main standardized variables
ZAGE	0.87	1.44±0.73
ZPFS: Proportion of forest and semi-natural habitats (%)	0.47	−2.04±1.35
ZPW Proportion of wetland (%)	0.34	3.93±2.25
ZEPGA edge proportion grassland–arable land (%)	−0.67	−1.23±0.76
Interactions terms
ZPFS-ZPW	–	−7.74±4.50
ZPFS-ZEPGA	–	−1.42±0.56**
Intercept	–	−4.01±0.85

Significant variables are highlighted in bold; **p<0.01.

Fig. 2 Total effects of the proportion of forest and semi-natural habitats, the proportion of wetland, and the edge proportion grassland–arable land on the presence or absence of Borrelia infection (without mediation) (a) and the impact of the proportion of forest and semi-natural habitats on the presence or absence of Borrelia infection (b).

Fig. 3 Boxplots of logit risk scores derived from the estimated equation in all participants, regardless of professions (a), in farmers (b), and in veterinarians (c).

Fig. 4 ROC curve.

Fig. 5 Borrelia serology results of the 11 participants notifying a history of Lyme disease.