Spatial analysis of positive and negative Q fever laboratory results for identifying high- and low-risk areas of infection in the Netherlands

Figures & data

Fig. 1 Incidence (×100,000 population) of Q fever laboratory tests (n =11,035) with locations of all small ruminant farms with ≥50 animals in the south of the Netherlands by four-digit postal code area. Data from patients testing positive in 2009 and 2010, and patients testing negative in 2010 at the laboratories in 's-Hertogenbosch (H) and Veldhoven (V).

Fig. 2 Proportion of positive test results based on the same data as in Fig. 1 with locations of infected goat farms.

Table 1 Characteristics of individuals with a positive or negative laboratory test result

	All	Positive		Negative		p
Variables	N	N	%	N	%
Sex
Male	5,507	2,224	55.4	3,283	46.7	p<0.001*
Female	5,528	1,787	44.6	3,741	53.3
	Mean	Mean	IQR	Mean	IQR
Age (years)	50.1	48.3	38–60	51.1	37–67	p<0.001**
Distance (km)^a	5.7	4.1	2.1–5.4	6.7	3.7–9.3	p<0.001***
All	11,035	4,011	36.4	7,024	63.7

IQR, interquartile range.

^aDistance between patient's home address and nearest infected dairy goat farm.

*Chi-square test, **Student's t-test, ***Mann–Whitney U test.

Table 2 Multivariate logistic regression analysis of risk factors associated with testing positive for Q fever

	All	Positive	Positive
Variables	N	N	%	Odds ratio	95% Confidence interval
Age (years)
0 ≤ 20	1,000	245	24.5	Reference
20 ≤ 60	6,236	2,722	43.7	2.71	2.31–3.19
60 ≤ 100	3,799	1,044	27.5	1.42	1.20–1.69
Sex
Male	5,507	2,224	40.4	1.52	1.40–1.66
Female	5,528	1,787	32.3	Reference
Distance^a (km)
< 1 km	345	229	66.4	21.70	16.28–28.92
1 ≤ 2 km	1,058	682	64.5	19.73	15.90–24.47
2 ≤ 4 km	2,682	1,162	43.3	8.16	6.76–9.86
4 ≤ 6 km	3,346	1,286	38.4	6.62	5.50–7.98
6 ≤ 8 km	1,260	405	32.1	5.14	4.17–6.34
8 ≤ 10 km	633	104	16.4	2.06	1.57–2.71
≥ 10 km	1,711	143	8.4	Reference
Total	11,035	4,011	36.4

^aDistance between patient's home address and nearest infected dairy goat farm.

Fig. 3 Proportion of patients testing positive for Q fever against mean distance from nearest infected dairy goat farm, per four-digit postal code area (n=262 postal codes areas).