Table 1.
Baseline characteristics across risk factors and unadjusted associations between risk factors and vivax infection rates
| 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 |
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)
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
cP value from the Mantel–Haenszel test of RR = 1.00