Incremental impact upon malaria transmission of supplementing pyrethroid-impregnated long-lasting insecticidal nets with indoor residual spraying using pyrethroids or the organophosphate, pirimiphos methyl

Table 3 Association of Anopheles funestus densities with different IRS insecticides supplementing LLINs upon months before, during and when not spraying

Indoor residual spraying insecticide treatment regimen	Absolute numbers caught	Mean catches^a	Relative biting rates of An. funestus
Indoor residual spraying insecticide treatment regimen	Absolute numbers caught	[95 % Confidence interval (CI)]	(RR)^a [95 % CI]	P value
Deltamethrin WG)
1–3 months since last spray	73	0.112 [0.641, 0.371]	0.99 [0.63, 1.56]	0.897
4–6 months since last spray	1229	0.641 [0.371, 1.109]	3.98 [3.15, 5.04]	<0.001
7–12 months since last spray	134	0.111 [0.062, 0.199]	0.86 [0.64, 1.17]	0.067
>12 months since last spray or never	1186	0.189 [0.113, 0.317]	1 [NA]^b	NA^b
Lambdacyhalothrin CS
1–3 months since last spray	20	0.191 [0.090, 0.405]	1.03 [0.56, 1.88]	0.805
4–6 months since last spray	6	0.055 [0.022, 0.141]	0.17 [0.08, 0.39]	<0.001
7–12 months since last spray	0	NE^c	NE^c	0.972
>12 months since last spray or never	182	0.198 [0.121]	1 [NA]^b	NA^b
Pirimiphosmethyl EC
1–3 months since last spray	478	0.234 [0.131, 0.417]	1.04 [0.83, 1.30]	0.786
4–6 months since last spray	346	0.055 [0.030, 0.098]	0.25 [0.20, 0.33]	<0.001
7–12 months since last spray	160	0.159 [0.086, 0.293]	0.69 [0.50, 0.95]	0.151
>12 months since last spray or never	2823	0.234 [0.131, 0.417]	1 [NA]^b	NA^b
Pirimiphosmethyl CS
1–3 months since last spray	14	0.021 [0.009, 0.047]	0.07 [0.04, 0.13]	<0.001
4–6 months since last spray	70	0.004 [0.002, 0.008]	0.02 [0.01, 0.02]	<0.001
7–12 months since last spray	NE^c	NE^c	NE^c	NE^c
>12 months since last spray or never	2087	0.253 [0.152, 0.422]	1 [NA]^b	NA

NA Not applicable because reference group, NE Not estimable because no spraying of this insecticide regimen was conducted early enough to yield impact data beyond 6 months post-spray but before the following spray round so no data are available for estimation
^aThe effect of different IRS treatment regimens on the mean catches of An. funestus species where estimated by fitting generalized linear mixed models (GLMMs) with An. funestus catches treated as dependent variables. The households where nested within villages which were also nested within the clusters, these together with date were treated as random effects, while the different IRS treatment regimens were categorized as independent variables. A Poisson distribution with no intercept was used to estimate the mean catches while an intercept was included in estimating the RR