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Table 2 Predictors of malaria incidence in a fixed cohort of 1,223 children, Liwonde, Malawi April—December 2013

From: The effectiveness of older insecticide-treated bed nets (ITNs) to prevent malaria infection in an area of moderate pyrethroid resistance: results from a cohort study in Malawi

Characteristic

Malaria infections, n

PYs at risk

Univariate

Multivariate

Observed iPPY (95% CI)

Rate ratio (95% CI)

p-value

Adjusted iPPY (95% CI)

Rate ratio (95% CI)

p-value

Age (months)

 6–11

18

19

0.90 (0.52–1.57)

0.70 (0.40–1.22)

0.211

0.63 (0.35–1.12)

0.51 (0.3–0.89)

0.017

 12+

805

620

1.29 (1.16–1.44)

Reference

–

1.22 (0.94–1.59)

Reference

–

Sex

 Female

396

317

1.24 (1.06–1.45)

0.95 (0.76–1.18)

0.626

   

 Male

429

322

1.31 (1.13–1.52)

Reference

–

   

ITN use

 Yes

798

620

1.27 (1.14–1.42)

0.94 (0.60–1.49)

0.801

0.80 (0.59–1.08)

0.83 (0.54–1.27)

0.389

 No

25

19

1.35 (0.86–2.13)

Reference

–

0.96 (0.58–1.6)

Reference

–

Member of first cohort

 Yes

495

344

1.43 (1.24–1.65)

1.29 (1.04–1.61)

0.0192

   

 No

330

296

1.1 (0.94–1.3)

Reference

–

   

Baseline Plasmodium infection

 Positive

375

152

2.44 (2.10–2.85)

2.67 (2.17–3.3)

< 0.001

   

 Negative

450

487

0.91 (0.79–1.06)

Reference

–

   

Inverse distance-weighted malaria prevalence

 Lowest

169

213

0.77 (0.62–0.97)

0.39 (0.30–0.52)

< 0.001

0.58 (0.38–0.89)

0.42 (0.31–0.57)

<0.001

 Middle

241

216

1.11 (0.92–1.34)

0.57 (0.44–0.72)

< 0.001

0.84 (0.56–1.25)

0.61 (0.48–0.78)

<0.001

 Highest

415

210

1.96 (1.68–2.29)

Reference

–

1.37 (0.96–1.97)

Reference

–

Malaria season

 Apr–June (high)

336

147

2.25 (1.99–2.55)

2.28 (1.97–2.65)

< 0.001

1.33 (0.93–1.92)

2.31 (1.98–2.7)

<0.001

 July–Dec (low)

488

493

0.99 (0.86–1.13)

Reference

–

0.58 (0.4–0.83)

Reference

–

Number of ITNs < 300 m

 Lowest

315

208

1.50 (1.26–1.79)

1.99 (1.49–2.65)

< 0.001

1.02 (0.69–1.49)

1.48 (1.1–2)

0.010

 Middle

345

217

1.58 (1.33–1.86)

2.08 (1.57–2.77)

< 0.001

0.97 (0.64–1.45)

1.41 (1.03–1.92)

0.031

 Highest

165

215

0.76 (0.60–0.95)

Reference

–

0.69 (0.46–1.02)

Reference

–

Altitude

 Lowest

251

217

1.14 (0.95–1.36)

1.25 (0.96–1.64)

0.101

0.94 (0.65–1.38)

1.60 (1.21–2.13)

0.001

 Middle

377

207

1.81 (1.52–2.14)

1.99 (1.52–2.59)

< 0.001

1.21 (0.82–1.8)

2.06 (1.57–2.69)

<0.001

Highest

197

216

0.91 (0.74–1.11)

Reference

–

0.59 (0.4–0.88)

Reference

–

Wealth index

 Poorest

285

212

1.34 (1.12–1.6)

1.46 (1.12–1.91)

0.006

0.89 (0.6–1.32)

1.26 (0.97–1.64)

0.085

 Middle

334

210

1.57 (1.31–1.87)

1.71 (1.31–2.23)

< 0.001

1.07 (0.74–1.56)

1.52 (1.18–1.97)

0.001

 Least poor

199

214

0.92 (0.75–1.12)

Reference

–

0.70 (0.47–1.05)

Reference

–

Caregiver completed primary school

 Yes

110

134

0.82 (0.60–1.11)

0.59 (0.42–0.81)

0.001

0.69 (0.44–1.07)

0.62 (0.45–0.85)

0.003

 No

708

503

1.39 (1.24–1.56)

Reference

–

1.12 (0.79–1.57)

Reference

–

  1. ITN insecticide-treated bed net, iPPY infections per person-year
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