title: The Effect of Indoor Residual Spraying on the Prevalence of Malaria Parasite Infection, Clinical Malaria and Anemia in an Area of Perennial Transmission and Moderate Coverage of Insecticide Treated Nets in Western Kenya.
abstract: BACKGROUND
  Insecticide treated nets (ITNs) and indoor residual spraying (IRS) have been scaled up for malaria prevention in sub-Saharan Africa. However, there are few studies on the benefit of implementing IRS in areas with moderate to high coverage of ITNs. We evaluated the impact of an IRS program on malaria related outcomes in western Kenya, an area of intense perennial malaria transmission and moderate ITN coverage (55-65% use of any net the previous night).
  
  
  METHODS
  The Kenya Division of Malaria Control, with support from the US President's Malaria Initiative, conducted IRS in one lowland endemic district with moderate coverage of ITNs. Surveys were conducted in the IRS district and a neighboring district before IRS, after one round of IRS in July-Sept 2008 and after a second round of IRS in April-May 2009. IRS was conducted with pyrethroid insecticides. At each survey, 30 clusters were selected for sampling and within each cluster, 12 compounds were randomly selected. The primary outcomes measured in all residents of selected compounds included malaria parasitemia, clinical malaria (P. falciparum infection plus history of fever) and anemia (Hb<8) of all residents in randomly selected compounds. At each survey round, individuals from the IRS district were matched to those from the non-IRS district using propensity scores and multivariate logistic regression models were constructed based on the matched dataset.
  
  
  RESULTS
  At baseline and after one round of IRS, there were no differences between the two districts in the prevalence of malaria parasitemia, clinical malaria or anemia. After two rounds of IRS, the prevalence of malaria parasitemia was 6.4% in the IRS district compared to 16.7% in the comparison district (OR = 0.36, 95% CI = 0.22-0.59, p<0.001). The prevalence of clinical malaria was also lower in the IRS district (1.8% vs. 4.9%, OR = 0.37, 95% CI = 0.20-0.68, p = 0.001). The prevalence of anemia was lower in the IRS district but only in children under 5 years of age (2.8% vs. 9.3%, OR = 0.30, 95% CI = 0.13-0.71, p = 0.006). Multivariate models incorporating both IRS and ITNs indicated that both had an impact on malaria parasitemia and clinical malaria but the independent effect of ITNs was reduced in the district that had received two rounds of IRS. There was no statistically significant independent effect of ITNs on the prevalence of anemia in any age group.
  
  
  CONCLUSIONS
  Both IRS and ITNs are effective tools for reducing malaria burden and when implemented in an area of moderate to high transmission with moderate ITN coverage, there may be an added benefit of IRS. The value of adding ITNs to IRS is less clear as their benefits may be masked by IRS. Additional monitoring of malaria control programs that implement ITNs and IRS concurrently is encouraged to better understand how to maximize the benefits of both interventions, particularly in the context of increasing pyrethroid resistance.
authors.affiliation: Division of Parasitic Diseases and Malaria, Center for Global Health, Centers for Disease Control and Prevention, Atlanta, Georgia, United States of America.
authors.forename: John E
authors.initials: JE
authors.lastname: Gimnig
authors.affiliation: Centre for Global Health Research, Kenya Medical Research Institute, Kisumu, Kenya.
authors.forename: Peter
authors.initials: P
authors.lastname: Otieno
authors.affiliation: Centre for Global Health Research, Kenya Medical Research Institute, Kisumu, Kenya.
authors.forename: Vincent
authors.initials: V
authors.lastname: Were
authors.affiliation: Centre for Global Health Research, Kenya Medical Research Institute, Kisumu, Kenya.
authors.forename: Doris
authors.initials: D
authors.lastname: Marwanga
authors.affiliation: Centre for Global Health Research, Kenya Medical Research Institute, Kisumu, Kenya.
authors.forename: Daisy
authors.initials: D
authors.lastname: Abong'o
authors.affiliation: Division of Parasitic Diseases and Malaria, Center for Global Health, Centers for Disease Control and Prevention, Atlanta, Georgia, United States of America.
authors.forename: Ryan
authors.initials: R
authors.lastname: Wiegand
authors.affiliation: Division of Parasitic Diseases and Malaria, Center for Global Health, Centers for Disease Control and Prevention, Atlanta, Georgia, United States of America.
authors.forename: John
authors.initials: J
authors.lastname: Williamson
authors.affiliation: Division of Parasitic Diseases and Malaria, Center for Global Health, Centers for Disease Control and Prevention, Atlanta, Georgia, United States of America.
authors.forename: Adam
authors.initials: A
authors.lastname: Wolkon
authors.affiliation: Eck Institute for Global Health, Department of Biological Sciences, University of Notre Dame, Notre Dame, Indiana, United States of America.
authors.forename: Ying
authors.initials: Y
authors.lastname: Zhou
authors.affiliation: Centre for Global Health Research, Kenya Medical Research Institute, Kisumu, Kenya.
authors.forename: M Nabie
authors.initials: MN
authors.lastname: Bayoh
authors.affiliation: Eck Institute for Global Health, Department of Biological Sciences, University of Notre Dame, Notre Dame, Indiana, United States of America.
authors.forename: Neil F
authors.initials: NF
authors.lastname: Lobo
authors.affiliation: Division of Parasitic Diseases and Malaria, Center for Global Health, Centers for Disease Control and Prevention, Atlanta, Georgia, United States of America.
authors.forename: Kayla
authors.initials: K
authors.lastname: Laserson
authors.affiliation: Centre for Global Health Research, Kenya Medical Research Institute, Kisumu, Kenya.
authors.forename: Simon
authors.initials: S
authors.lastname: Kariuki
authors.affiliation: Division of Parasitic Diseases and Malaria, Center for Global Health, Centers for Disease Control and Prevention, Atlanta, Georgia, United States of America.
authors.forename: Mary J
authors.initials: MJ
authors.lastname: Hamel
mesh_terms: D000293:Adolescent; D000328:Adult; D000336:Aerosols; D000740:Anemia / Q000453:epidemiology / Q000517:prevention & control*; D002648:Child; D003430:Cross-Sectional Studies; D005260:Female; D005843:Geography; D006790:Host-Parasite Interactions / Q000187:drug effects; D006798:Housing; D006801:Humans; D057148:Insecticide-Treated Bednets / Q000706:statistics & numerical data*; D007306:Insecticides / Q000008:administration & dosage / Q000494:pharmacology*; D007630:Kenya / Q000453:epidemiology; D016015:Logistic Models; D016778:Malaria, Falciparum / Q000453:epidemiology / Q000469:parasitology / Q000517:prevention & control*; D008297:Male; D015999:Multivariate Analysis; D017063:Outcome Assessment, Health Care / Q000379:methods / Q000706:statistics & numerical data; D010963:Plasmodium falciparum / Q000187:drug effects* / Q000502:physiology; D015995:Prevalence; D011722:Pyrethrins / Q000008:administration & dosage / Q000494:pharmacology*; D013997:Time Factors; D055815:Young Adult
chemical_list: D000336:Aerosols; D007306:Insecticides; D011722:Pyrethrins