Risk factors and potential preventive measures for nephropatia epidemica in Sweden 2011–2012: a case–control study

Figures & data

Fig. 1.  The NE incidence in Sweden in the study period (June 2011–July 2012).

Fig. 2.  Age and sex distribution of cases and controls, NE study, Sweden 2011–2012.

Table 1 Distribution of cases and controls by reporting county, NE study, Sweden 2011–2012

	Västerbotten	Norrbotten	Västernorrland	Jämtland	Total
Cases reported in SmiNet	59	50	34	28	171
Cases included in analysis	49	30	20	15	114
Controls included in analysis	124	79	47	50	300

Table 2 Matched odds-ratios (mOR) with 95% confidence intervals (95% CIs) and p value through conditional logistic regression for various exposures, Sweden 2011–2012

	Cases		Controls
Exposure	n/N	(%)	n/N	%	mOR (95% CI)	p
Occupational risk factors
Mowing the lawn	43/106	41	57/267	21	5 (2.3–11)	<0.001
Vacuuming a summer house	24/69	35	21/190	11	4.7 (1.8–12)	0.001
Making house repairs	20/110	18	21/296	7	3.6 (1.5–8.6)	0.003
Visiting a summer house	51/113	45	94/299	31	2.2 (1.2–3.8)	0.004
Pulling weeds	29/106	27	51/267	19	2.7 (1.3–5.6)	0.005
Using a chainsaw	17/114	15	18/299	6	2.7 (1.2–5.8)	0.012
Dry-sweeping a summer house	25/62	40	27/157	17	3.6 (1.3–9.6)	0.012
Spending free time in the woods	89/114	78	197/298	66	1.9 (1.03–3.5)	0.037
Carrying wood	77/113	68	177/278	59	1.4 (0.8–2.4)	0.198
Farming	16/109	15	26/291	9	1.6 (0.8–3.5)	0.203
Working in the woods	38/111	34	86/295	29	1.2 (0.7–2.2)	0.435
Cutting wood	38/113	32	87/299	29	1.2 (0.6–2)	0.627
Raking leaves or grass	26/106	25	66/267	25	1.1 (0.6–2)	0.825
Working with hay	13/111	12	22/294	7	1 (0.4–2.6)	0.897
Environmental risk factors
Living in a wooden summer house	28/114	25	22/300	7	4.8 (2.2–10.2)	<0.001
Living in a house with open space beneath	59/102	58	78/276	28	4.4 (2.4–8.1)	<0.001
Living in a house with concrete foundation^a	9/102	9	86/276	31	0.16 (0.07–0.4)	<0.001
Living less than 50 m from a forest	75/112	67	132/293	45	2.4 (1.4–4.1)	0.001
Living in a house made of brick or stone^a	4/114	4	28/300	10	0.14 (0.03–0.65)	0.011
Rodent related risk factors
Noticing rodents	53/114	46	51/298	17	6.7 (3.4–13.4)	<0.001
Noticing rodent droppings	57/114	50	54/298	18	7.6 (3.7–15.4)	<0.001
Cleaning rodent droppings	61/113	54	90/296	30	2.8 (1.6–4.8)	0.000
Using rodent traps	36/114	32	63/295	21	1.6 (0.9–2.9)	0.093
Using rodent poison	10/114	9	21/295	7	1.2 (0.5–2.8)	0.750
Other risk factors
Previous knowledge about NE^a	30/35	85	285/298	96	0.14 (0.03–0.8)	0.027
Owning a cat	27/112	24	95/299	32	0.6 (0.8–1.1)	0.080
Smoking	24/110	22	42/296	14	1.6 (0.8–2.9)	0.172

^aVariable not included in the multivariable model.

n=cases exposed; N=total cases replying to the question.

Table 3 Descriptive data on potential preventive measures, NE case–control study, Sweden 2011–2012

	Always		>50%		<50%		Never
Potential preventive measure	Cases	Controls	Cases	Controls	Cases	Controls	Cases	Controls
Wearing mask when doing repairs (N=34)	3/16 (19%)	1/18 (6%)	2/16 (12%)	2/18 (11%)	1/16 (6%)	3/18 (17%)	10/16 (63%)	12/18 (66%)
Wearing mask when cleaning rodent droppings (N=129)	4/50 (8%)	2/79 (3%)	1/50 (2%)	1/79 (1%)	4/50 (8%)	5/79 (6%)	41/50 (52%)	71/79 (90%)
Wearing mask when mowing the lawn (N=97)	0/42 (0%)	1/55 (2%)	2/42 (5%)	1/55 (2%)	1/42 (2%)	2/55 (4%)	39/42 (93%)	51/55 (92%)
Wearing gloves when doing repairs (N=32)	6/15 (40%)	9/17 (53%)	6/15 (40%)	3/17 (18%)	1/15 (7%)	2/17 (11%)	2/15 (13%)	3/17 (18%)
Wearing gloves when cleaning droppings (N=128)	26/52 (50%)	35/76 (46%)	7/52 (13%)	13/76 (17%)	10/52 (20%)	15/76 (20%)	9/52 (17%)	13/76 (17%)
Wearing gloves when mowing the lawn (N=96)	7/42 (28%)	17/54 (31%)	7/42 (28%)	9/54 (17%)	12/42 (28%)	9/54 (17%)	16/42 (38%)	19/54 (35%)
Washing hands after doing repairs (N=35)	8/16 (50%)	6/19 (31%)	5/16 (31%)	3/19 (16%)	2/16 (13%)	6/19 (31%)	1/16 (6%)	4/19 (22%)
Washing hands after cleaning droppings (N=138)	39/57 (68%)	45/81 (56%)	7/57 (12%)	13/81 (16%)	8/57 (14%)	18/81 (22%)	3/57 (6%)	5/81 (4%)
Washing hands after mowing the lawn (N=97)	6/43 (14%)	19/54 (35%)	11/43 (26%)	16/54 (29%)	22/43 (51%)	14/54 (26%)	4 (9%)	15/54 (10%)

N=number of valid replies from cases and controls.

Table 4 Adjusted mOR with 95% confidence intervals (CIs) and p values, Sweden 2011–2012

Exposure	Adjusted mOR (95% CI)	p
Occupational risk factors
Making house repairs	11 (1.6–73.9)	0.014
Mowing the lawn	3.7 (0.7–20)	0.121
Visiting a summer house	1.6 (0.5–5.0)	0.393
Pulling weeds	1.9 (0.4–9.8)	0.441
Spending free time in the woods	0.7 (0.2–2.2)	0.578
Using a chainsaw	1.4 (0.3–5.7)	0.636
Carrying wood	0.8 (0.3–2.4)	0.749
Environmental risk factors
Living in a house with open space beneath	4.3 (1.4–13.3)	0.012
Living less than 50 m from a forest	2.6 (1.03–6.8)	0.043
Living in wooden summer house	1.8 (0.4–9.3)	0.479
Rodent related risk factors
Noticing rodents	6.8 (1.6–28,4)	0.008
Noticing rodent droppings	2.4 (0.7–8.4)	0.152
Handling mice	0.37 (0.1–2.2)	0.287
Using rodent traps	1.4 (0.5–4.1)	0.514
Cleaning rodent droppings	0.9 (0.3–2.9)	0.894
Other risk factors
Smoking	5.7 (1.4–23.9)	0.017
Owning a cat	0.7 (0.2–2.4)	0.605