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Table 1 Baseline characteristics across risk factors and unadjusted associations between risk factors and vivax infection rates

From: Proximity to vector breeding site and risk of Plasmodium vivax infection: a prospective cohort study in rural Ethiopia

Participant characteristics

No. of individuals (%)

No. with infection

Follow-up (per-years)

Rate/1000 per-years

Rate ratio (RR)

95% conf. interval

P valuec

Household distance to breeding site (n = 8121), m

 > 2700

2460 (30.3)

26

3670.0

7.08

Ref

  

 2400–2700

2527 (31.1)

33

3691.5

8.94

1.26

0.76–2.11

0.37

 2100–2400

1751 (21.6)

38

2472.5

15.37

2.17

1.32–3.57

0.002

 < 2100

1383 (17.0)

49

2044.1

23.97

3.38

2.10–5.44

< 0.001

Age at study entry (n = 8121), years

 ≥ 25

2558 (31.5)

16

4056.8

3.94

Ref

  

 15–24

2321 (28.6)

19

2732.8

6.95

1.76

0.91–3.43

0.09

 5–14

2175 (26.8)

69

3435.4

20.08

5.09

2.96–8.77

< 0.001

 0–4

1067 (13.1)

42

1653.1

25.41

6.44

3.62–11.46

< 0.001

Gender (n = 8121)

 Male

4227 (52.1)

82

6045.4

13.56

Ref

  

 Female

3894 (47.9)

64

5832.7

10.97

0.81

0.58–1.12

0.20

Household wealth (n = 8121)

 1 = wealthiest tertile

2282 (28.1)

45

3177.5

14.16

Ref

  

 2

3079 (37.9)

47

4599.3

10.22

0.72

0.48–1.09

0.12

 3 = poorest tertile

2760 (34.0)

54

4101.3

13.17

0.93

0.63–1.38

0.72

Education head of household (n = 8121)

 Secondary or above

1720 (21.2)

26

2574.8

10.10

Ref

  

 Primary

2050 (25.2)

43

3014.7

14.26

1.41

0.87–2.30

0.16

 No education

4351 (53.6)

77

6288.6

12.24

1.21

0.78–1.89

0.39

Persons living in household (n = 8121)a

 ≤ 7

4445 (54.7)

73

6619.1

11.03

Ref

  

 ≥ 8

3676 (45.3)

73

5259.0

13.88

1.26

0.91–1.74

0.16

Time-period

 Period 1 (week 1–48)

–

76

5797.7

13.11

Ref

  

 Period 2 (week 49–101)

–

70

6080.4

11.51

0.88

0.64–1.22

0.43

ITN use fractionb

 Complete follow-up period (n = 8096) (%)

  > 50

2878 (35.6)

32

4925.0

6.50

Ref

  

  ≤ 50

5218 (64.4)

109

6952.2

15.68

2.41

1.63–3.58

< 0.001

 Period 1 (week 1–48) (n = 7016) (%)

  > 50

1314 (18.7)

16

1167.5

13.70

Ref

  

  ≤ 50

5702 (81.3)

55

4629.3

11.88

0.87

0.50–1.51

0.62

 Period 2 (week 49–101) (n = 6695) (%)

  > 50

4163 (62.2)

34

4029.0

8.44

Ref

  

  ≤ 50

2532 (37.8)

36

2051.4

17.55

2.08

1.30–3.32

0.002

  1. aThe number of persons per household ranged from 1 to 17, with a mean of 5.9 and a median of 7 (used as the cut-off point)
  2. bITN use was recorded weekly (starting from week 5) during the regular follow-up visits to households. Participants were asked if they slept under an ITN the night before the visit. Use fraction was calculated as the number of nights reportedly sleeping under a ITN divided by the total number of nights asked. At week 48, there was a net distribution campaign in the Kebele, thus use fraction is presented both for the complete follow-up period as well as with the follow-up period split in two. For those with P. vivax infection, ITN use fraction was calculated only for weeks prior to infection
  3. cP value from the Mantel–Haenszel test of RR = 1.00
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Malaria Journal

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