title: Durability of Olyset campaign nets distributed between 2009 and 2011 in eight districts of Tanzania.
abstract: BACKGROUND
  Long-lasting insecticidal nets (LLINs) are the first line choice for malaria vector control in sub-Saharan Africa, with most countries adopting universal coverage campaigns. However, there is only limited information on LLIN durability under user conditions. Therefore, this study aimed to assess the durability of Olyset(®) LLINs distributed during campaigns between 2009 and 2011 in Tanzania.
  
  
  METHODS
  A retrospective field survey was conducted in eight districts in Tanzania mainland to assess the durability of Olyset campaign nets. Household questionnaires were used to assess attrition, i.e. net loss. All nets remaining in households were collected. A sub-sample of 198 Olyset campaign nets was examined for bio-efficacy against Anopheles gambiae s.s. mosquitoes, permethrin content and physical integrity following standard World Health Organization (WHO) methods.
  
  
  RESULTS
  Of 6067 campaign nets reported to have been received between 2009 and 2011, 35% (2145 nets) were no longer present. Most of those nets had been discarded (84%) mainly because they were too torn (94%). Of the 198 sub-sampled Olyset LLINs, 61% were still in serviceable physical condition sufficient to provide personal protection while 39% were in unserviceable physical condition according to WHO proportionate Hole Index (pHI). More than 96% (116/120) of nets in serviceable condition passed WHO bioefficacy criteria while all nets in unserviceable condition passed WHO bioefficacy criteria. Overall mean permethrin content was 16.5 g/kg (95% CI 16.2-16.9) with 78% of the sub-sampled nets retaining recommended permethrin content regardless of their age or physical condition. Nets aged 4 years and above had a mean permethrin content of 14 g/kg (95% CI 12.0-16.0). The only statistically significant predictor of reduced physical net integrity was rats in the house.
  
  
  CONCLUSIONS
  Two-to-four years after a mass campaign, only 39% of distributed nets remain both present and in serviceable physical condition, a functional survival considerably below WHO assumptions of 50% survival of a 'three-year' net. However, the majority of nets still retained substantial levels of permethrin and could still be bio-chemically useful against mosquitoes if their holes were repaired, adding evidence to the value of net care and repair campaigns.
authors.affiliation: Epidemiology and Public Health Department, Swiss Institute of Tropical and Public Health, Soccinstrase 57, 4002, Basel, Switzerland. d.massue@unibas.ch.|University of Basel, Petersplatz 1, 4003, Basel, Switzerland. d.massue@unibas.ch.|National Institute for Medical Research, Amani Research Centre, Muheza, P. O. Box 81, Tanga, Tanzania. d.massue@unibas.ch.
authors.forename: Dennis J
authors.initials: DJ
authors.lastname: Massue
authors.affiliation: University of Basel, Petersplatz 1, 4003, Basel, Switzerland.|National Institute for Medical Research, Amani Research Centre, Muheza, P. O. Box 81, Tanga, Tanzania.|Ifakara Health Institute, Bagamoyo Research and Training Centre, Bagamoyo, P.O. Box 74, Pwani, Tanzania.
authors.forename: Sarah J
authors.initials: SJ
authors.lastname: Moore
authors.affiliation: Ifakara Health Institute, Bagamoyo Research and Training Centre, Bagamoyo, P.O. Box 74, Pwani, Tanzania.|Department of Disease Control, Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, WC1E 7HT, UK.
authors.forename: Zawadi D
authors.initials: ZD
authors.lastname: Mageni
authors.affiliation: Ifakara Health Institute, Bagamoyo Research and Training Centre, Bagamoyo, P.O. Box 74, Pwani, Tanzania.|Department of Disease Control, Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, WC1E 7HT, UK.
authors.forename: Jason D
authors.initials: JD
authors.lastname: Moore
authors.affiliation: MRC Tropical Epidemiology Group, London School of Hygiene and Tropical Medicine, London, WC1E 7HT, UK.
authors.forename: John
authors.initials: J
authors.lastname: Bradley
authors.affiliation: Plant Protection Products and Biocides Physico-chemistry and Residues Unit, Agriculture and Natural Environment Department, Walloon Agricultural Research Centre (CRA-W), Gembloux, Belgium.
authors.forename: Olivier
authors.initials: O
authors.lastname: Pigeon
authors.affiliation: Ifakara Health Institute, Bagamoyo Research and Training Centre, Bagamoyo, P.O. Box 74, Pwani, Tanzania.
authors.forename: Erasto J
authors.initials: EJ
authors.lastname: Maziba
authors.affiliation: National Malaria Control Programme, Dar Es Salaam, Tanzania.
authors.forename: Renata
authors.initials: R
authors.lastname: Mandike
authors.affiliation: University of Basel, Petersplatz 1, 4003, Basel, Switzerland.|National Malaria Control Programme, Dar Es Salaam, Tanzania.
authors.forename: Karen
authors.initials: K
authors.lastname: Kramer
authors.affiliation: Epidemiology and Public Health Department, Swiss Institute of Tropical and Public Health, Soccinstrase 57, 4002, Basel, Switzerland.
authors.forename: William N
authors.initials: WN
authors.lastname: Kisinza
authors.affiliation: Institut de Recherche pour le Développement (IRD), MIVEGEC, Montpellier, France.|Department of Entomology, Kasetsart University, Bangkok, Thailand.|Department of Mathematical Sciences and Technology, Norwegian University of Life Sciences, Ås, Norway.
authors.forename: Hans J
authors.initials: HJ
authors.lastname: Overgaard
authors.affiliation: Ifakara Health Institute, Bagamoyo Research and Training Centre, Bagamoyo, P.O. Box 74, Pwani, Tanzania.|Department of Disease Control, Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, WC1E 7HT, UK.
authors.forename: Lena M
authors.initials: LM
authors.lastname: Lorenz
mesh_terms: D000818:Animals; D000852:Anopheles / Q000187:drug effects; D001681:Biological Assay; D003430:Cross-Sectional Studies; D005191:Family Characteristics; D006801:Humans; D057148:Insecticide-Treated Bednets / Q000706:statistics & numerical data*; D007306:Insecticides / Q000032:analysis / Q000494:pharmacology; D009032:Mosquito Control / Q000379:methods*; D026023:Permethrin / Q000032:analysis / Q000494:pharmacology; D012189:Retrospective Studies; D011795:Surveys and Questionnaires; D013636:Tanzania
chemical_list: D007306:Insecticides; D026023:Permethrin
keywords: Attrition; Bio-efficacy; Chemical content; Durability; LLINs; Olyset; Physical integrity; Tanzania; Universal coverage campaign