title: Malaria risk factors in North West Tanzania: the effect of spraying, nets and wealth.
abstract: Malaria prevalence remains high in many African countries despite massive scaling-up of insecticide treated nets (ITN) and indoor residual spraying (IRS). This paper evaluates the protective effect of pyrethroid IRS and ITNs in relation to risk factors for malaria based on a study conducted in North-West Tanzania, where IRS has been conducted since 2007 and universal coverage of ITNs has been carried out recently. In 2011 community-based cross-sectional surveys were conducted in the two main malaria transmission periods that occur after the short and long rainy seasons. These included 5,152 and 4,325 children aged 0.5-14 years, respectively. Data on IRS and ITN coverage, household demographics and socio-economic status were collected using an adapted version of the Malaria Indicator Survey. Children were screened for malaria by rapid diagnostic test. In the second survey, haemoglobin density was measured and filter paper blood spots were collected to determine age-specific sero-prevalence in each community surveyed. Plasmodium falciparum infection prevalence in children 0.5-14 years old was 9.3% (95%CI:5.9-14.5) and 22.8% (95%CI:17.3-29.4) in the two surveys. Risk factors for infection after the short rains included households not being sprayed (OR = 0.39; 95%CI:0.20-0.75); low community net ownership (OR = 0.45; 95%CI:0.21-0.95); and low community SES (least poor vs. poorest tertile: OR = 0.13, 95%CI:0.05-0.34). Risk factors after the long rains included household poverty (per quintile increase: OR = 0.89; 95%CI:0.82-0.97) and community poverty (least poor vs. poorest tertile: OR = 0.26, 95%CI:0.15-0.44); household IRS or high community ITN ownership were not protective. Despite high IRS coverage and equitable LLIN distribution, poverty was an important risk factor for malaria suggesting it could be beneficial to target additional malaria control activities to poor households and communities. High malaria prevalence in some clusters and the limited protection given by pyrethroid IRS and LLINs suggest that it may be necessary to enhance established vector control activities and consider additional interventions.
authors.affiliation: Department of Infectious Disease Epidemiology, London School of Tropical Medicine and Hygiene, London, United Kingdom. philippa.west@lshtm.ac.uk
authors.forename: Philippa A
authors.initials: PA
authors.lastname: West
authors.forename: Natacha
authors.initials: N
authors.lastname: Protopopoff
authors.forename: Mark
authors.initials: M
authors.lastname: Rowland
authors.forename: Emma
authors.initials: E
authors.lastname: Cumming
authors.forename: Alison
authors.initials: A
authors.lastname: Rand
authors.forename: Chris
authors.initials: C
authors.lastname: Drakeley
authors.forename: Alexandra
authors.initials: A
authors.lastname: Wright
authors.forename: Zuhura
authors.initials: Z
authors.lastname: Kivaju
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Kirby
authors.forename: Franklin W
authors.initials: FW
authors.lastname: Mosha
authors.forename: William
authors.initials: W
authors.lastname: Kisinza
authors.forename: Immo
authors.initials: I
authors.lastname: Kleinschmidt
mesh_terms: D000293:Adolescent; D002648:Child; D002675:Child, Preschool; D016000:Cluster Analysis; D005191:Family Characteristics; D005260:Female; D006306:Health Surveys; D006801:Humans; D007223:Infant; D057148:Insecticide-Treated Bednets / Q000706:statistics & numerical data*; D007306:Insecticides / Q000633:toxicity*; D016778:Malaria, Falciparum / Q000191:economics* / Q000453:epidemiology* / Q000469:parasitology; D008297:Male; D009032:Mosquito Control / Q000706:statistics & numerical data; D010963:Plasmodium falciparum / Q000502:physiology; D015995:Prevalence; D012307:Risk Factors; D012959:Socioeconomic Factors; D013636:Tanzania / Q000453:epidemiology
chemical_list: D007306:Insecticides