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Indoor residual spraying for preventing malaria in communities using insecticide-treated nets.

Pryce, Joseph, Medley, Nancy and Choi, Leslie (2022) 'Indoor residual spraying for preventing malaria in communities using insecticide-treated nets.'. Cochrane Database of Systematic Reviews, Vol 1, CD012688.

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Insecticide‐treated nets (ITNs) and indoor residual spraying (IRS) are used to prevent malaria transmission. Both interventions use insecticides to kill mosquitoes that bite and rest indoors. Adding IRS to ITNs may improve malaria control simply because two interventions can be better than one. Furthermore, IRS may improve malaria control where ITNs are failing due to insecticide resistance. Pyrethroid insecticides are the predominant class of insecticide used for ITNs, as they are more safe than other insecticide classes when in prolonged contact with human skin. While many mosquito populations have developed some resistance to pyrethroid insecticides, a wider range of insecticides can be used for IRS. This review is an update of the previous Cochrane 2019 edition.


To summarize the effect on malaria of additionally implementing IRS, using non‐pyrethroid‐like or pyrethroid‐like insecticides, in communities currently using ITNs.

Search methods

We searched the Cochrane Infectious Diseases Group Specialized Register; CENTRAL; MEDLINE; and five other databases for records from 1 January 2000 to 8 November 2021, on the basis that ITN programmes did not begin to be implemented as policy before the year 2000.

Selection criteria

We included cluster‐randomized controlled trials (cRCTs), interrupted time series (ITS), or controlled before‐after studies (CBAs) comparing IRS plus ITNs with ITNs alone. We included studies with at least 50% ITN ownership (defined as the proportion of households owning one or more ITN) in both study arms.

Data collection and analysis

Two review authors independently assessed studies for eligibility, analyzed risk of bias, and extracted data. We used risk ratio (RR) and 95% confidence intervals (CI). We stratified by type of insecticide, 'pyrethroid‐like' and 'non‐pyrethroid‐like'; the latter could improve malaria control better than adding IRS insecticides that have the same way of working as the insecticide on ITNs ('pyrethroid‐like'). We used subgroup analysis of ITN usage in the studies to explore heterogeneity. We assessed the certainty of evidence using the GRADE approach.

Main results

Eight cRCTs (10 comparisons), one CBA, and one ITS study, all conducted since 2008 in sub‐Saharan Africa, met our inclusion criteria. The primary vectors in all sites were mosquitoes belonging to the Anopheles gambiae s.l. complex species; five studies in Benin, Mozambique, Ghana, Sudan, and Tanzania also reported the vector Anopheles funestus. Five cRCTs and both quasi‐experimental design studies used insecticides with targets different to pyrethroids (two used bendiocarb, three used pirimiphos‐methyl, and one used propoxur. Each of these studies were conducted in areas where the vectors were described as resistant or highly resistant to pyrethroids. Two cRCTs used dichloro‐diphenyl‐trichlorethane (DDT), an insecticide with the same target as pyrethroids. The remaining cRCT used both types of insecticide (pyrethroid deltamethrin in the first year, switching to bendiocarb for the second year).

Indoor residual spraying using 'non‐pyrethroid‐like' insecticides

Six studies were included (four cRCTs, one CBA, and one ITS). Our main analysis for prevalence excluded a study at high risk of bias due to repeated sampling of the same population. This risk did not apply to other outcomes. Overall, the addition of IRS reduced malaria parasite prevalence (RR 0.61, 95% CI 0.42 to 0.88; 4 cRCTs, 16,394 participants; high‐certainty evidence). IRS may also reduce malaria incidence on average (rate ratio 0.86, 95% CI 0.61 to 1.23; 4 cRCTs, 323,631 child‐years; low‐certainty evidence) but the effect was absent in two studies. Subgroup analyses did not explain the qualitative heterogeneity between studies. One cRCT reported no effect on malaria incidence or parasite prevalence in the first year, when a pyrethroid‐like insecticide was used for IRS, but showed an effect on both outcomes in the second year, when a non‐pyrethroid‐like IRS was used.

The addition of IRS may also reduce anaemia prevalence (RR 0.71, 95% CI 0.38 to 1.31; 3 cRCTs, 4288 participants; low‐certainty evidence). Four cRCTs reported the impact of IRS on entomological inoculation rate (EIR), with variable results; overall, we do not know if IRS had any effect on the EIR in communities using ITNs (very low‐certainty evidence). Studies also reported the adult mosquito density and the sporozoite rate, but we could not summarize or pool these entomological outcomes due to differences in the reported data. Three studies measured the prevalence of pyrethroid resistance before and after IRS being introduced: there was no difference detected, but these data are limited.

Indoor residual spraying using 'pyrethroid‐like' insecticides

Adding IRS using a pyrethroid‐like insecticide did not appear to markedly alter malaria incidence (rate ratio 1.07, 95% CI 0.80 to 1.43; 2 cRCTs, 15,717 child‐years; moderate‐certainty evidence), parasite prevalence (RR 1.11, 95% CI 0.86 to 1.44; 3 cRCTs, 10,820 participants; moderate‐certainty evidence), or anaemia prevalence (RR 1.12, 95% CI 0.89 to 1.40; 1 cRCT, 4186 participants; low‐certainty evidence). Data on EIR were limited so no conclusion was made (very low‐certainty evidence).

Authors' conclusions

in communities using ITNs, the addition of IRS with 'non‐pyrethroid‐like' insecticides was associated with reduced malaria prevalence. Malaria incidence may also be reduced on average, but there was unexplained qualitative heterogeneity, and the effect may therefore not be observed in all settings.

When using 'pyrethroid‐like' insecticides, there was no detectable additional benefit of IRS in communities using ITNs.

Item Type: Article
Additional Information: This is an update review. Earlier versions can be viewed here and here
Subjects: WA Public Health > Preventive Medicine > WA 110 Prevention and control of communicable diseases. Transmission of infectious diseases
WA Public Health > Preventive Medicine > WA 240 Disinfection. Disinfestation. Pesticides (including diseases caused by)
WC Communicable Diseases > Tropical and Parasitic Diseases > WC 750 Malaria
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Item titleItem URI
Indoor residual spraying for preventing malaria in communities using insecticide-treated nets
The combination of indoor residual spraying with insecticide-treated nets versus insecticide-treated nets alone for preventing malaria (Protocol)
Faculty: Department: Biological Sciences > Vector Biology Department
Clinical Sciences & International Health > Clinical Sciences Department
Digital Object Identifer (DOI):
SWORD Depositor: JISC Pubrouter
Depositing User: JISC Pubrouter
Date Deposited: 31 Jan 2022 12:05
Last Modified: 31 Jan 2022 12:10


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