A cohort study of the effectiveness of insecticide-treated bed nets to prevent malaria in an area of moderate pyrethroid resistance, Malawi

Lindblade, Kim A; Mwandama, Dyson; Mzilahowa, Themba; Steinhardt, Laura; Gimnig, John; Shah, Monica; Bauleni, Andy; Wong, Jacklyn; Wiegand, Ryan; Howell, Paul; Zoya, John; Chiphwanya, John; Mathanga, Don P

doi:10.1186/s12936-015-0554-1

Table 3 Predictors of malaria incidence in a fixed cohort of 1,199 children age six to 59 months at baseline, Liwonde, Malawi 2012- 2013 ^a

From: A cohort study of the effectiveness of insecticide-treated bed nets to prevent malaria in an area of moderate pyrethroid resistance, Malawi

				Univariate			Multivariate
Characteristic		Malaria infections (n)	Person-years at risk	Observed incidence PPY	Rate ratio (95% CI)	P value	Adjusted incidence ^b PPY (95% CI)	Rate ratio (95% CI)	P value
Age (months)	6-11	64	17	3.7 (2.7-5.0)	2.2 (1.6-3.0)	<0.0001	2.1 (1.5-2.9)	1.0 (0.8-1.4)	0.84
	12+	1845	891	1.7 (1.6-1.8)	1.0		2.0 (1.8-2.3)	1.0
Sex	Female	905	433	1.7 (1.6-1.9)	1.0 (0.9-1.1)	0.96
	Male	1004	471	1.7 (1.6-1.9)	1.0
Baseline Plasmodium infection	Positive	948	329	2.4 (2.2-2.7)	1.7 (1.5-2.0)	<0.0001	2.7 (2.2-3.3)	1.7 (1.5-1.9)	<0.0001
Baseline Plasmodium infection	Negative	960	573	1.4 (1.3-1.5)	1.0		1.6 (1.3-2.0)	1.0
Bed net use	ITN	1710	864	1.6 (1.5-1.7)	0.4 (0.3-0.5)	<0.0001	1.7 (1.5-2.1)	0.7 (0.5-0.8)	<0.0001
	UTN	92	17	4.9 (4.1-5.9)	1.1 (0.8-1.5)	0.53	2.0 (1.6-2.6)	0.8 (0.6-1.0)	0.06
	No bed net	86	15	4.4 (3.5-5.7)	1.0		2.6 (2.0-3.3)	1.0
Wealth index	Poorest	725	290	2.1 (1.9-2.3)	1.5 (1.3-1.8)	<0.0001	2.3 (1.9-2.8)	1.3 (1.1-1.5)	0.0008
	Middle	647	296	1.8 (1.6-2.0)	1.3 (1.1-1.6)	0.001	2.2 (1.8-2.7)	1.2 (1.1-1.5)	0.01
	Least poor	495	309	1.4 (1.2-1.6)	1.0		1.8 (1.4-2.2)	1.0
Caregiver completed primary	Yes	239	164	1.2 (0.9-1.4)	0.6 (0.5-0.8)	<0.0001	1.9 (1.5-2.4)	0.8 (0.7-1.0)	0.02
Caregiver completed primary	No	1628	730	1.9 (1.7-2.0)	1.0		2.3 (1.9-2.8)	1.0
Altitude	Lowest	680	300	1.9 (1.7-2.1)	1.4 (1.2-1.7)	0.0001	2.4 (1.9-2.9)	1.5 (1.3-1.8)	<0.0001
	Middle	727	294	2.1 (1.9-2.4)	1.6 (1.3-1.9)	<0.0001	2.4 (2.0-2.9)	1.5 (1.3-1.8)	<0.0001
	Highest	497	307	1.3 (1.2-1.5)	1.0		1. (1.3-2.0)	1.0
Number of ITNs <300 m	Lowest	586	249	2.0 (1.8-2.3)	1.7 (1.4-2.1)	<0.0001	2.1 (1.7-2.6)	1.1 (0.9-1.4)	0.39
Number of ITNs <300 m	Middle	737	313	2.1 (1.9-2.3)	1.7 (1.5-2.1)	<0.0001	2.2 (1.8-2.7)	1.2 (0.9-1.4)	0.17
	Highest	389	272	1.2 (1.0-1.4)	1.0		1.9 (1.5-2.4)	1.0
IDW malaria prevalence	Lowest	474	294	1.3 (1.1-1.5)	0.6 (0.5-0.7)	<0.0001	1.7 (1.3-2.1)	0.7 (0.5-0.8)	0.0002
IDW malaria prevalence	Middle	610	304	1.7 (1.5-1.9)	0.8 (0.6-0.9)	0.0003	2.2 (1.7-2.7)	0.9 (0.7-1.0)	0.04
	Highest	820	302	2.3 (2.1-2.5)	1.0		2.5 (2.1-3.1)	1.0
Season	Apr-June	844	178	4.1 (3.8-4.4)	2.3 (2.0-2.7)	<0.0001	4.6 (3.9-5.5)	2.3 (2.0-2.6)	<0.0001
	July-Dec	556	486	0.9 (0.8-1.0)	0.5 (0.4-0.6)	<0.0001	1.0 (0.8-1.2)	0.5 (0.4-0.6)	<0.0001
	Jan-Mar	509	241	1.8 (1.6-2.0)	1.0		2.0 (1.6-2.5)	1.0

^a PPY = per person year; IDW = inverse distance-weighted; ITN = insecticide-treated bed net; UTN = untreated bed net; CI = confidence interval.
^b Incidence is model-adjusted for all other variables in the column.

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