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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