title: Spatially aggregated clusters and scattered smaller loci of elevated malaria vector density and human infection prevalence in urban Dar es Salaam, Tanzania.
abstract: BACKGROUND
  Malaria transmission, primarily mediated by Anopheles gambiae, persists in Dar es Salaam (DSM) despite high coverage with bed nets, mosquito-proofed housing and larviciding. New or improved vector control strategies are required to eliminate malaria from DSM, but these will only succeed if they are delivered to the minority of locations where residual transmission actually persists. Hotspots of spatially clustered locations with elevated malaria infection prevalence or vector densities were, therefore, mapped across the city in an attempt to provide a basis for targeting supplementary interventions.
  
  
  METHODS
  Two phases of a city-wide population-weighted random sample of cross-sectional household surveys of malaria infections were complemented by two matching phases of geographically overlapping, high-resolution, longitudinal vector density surveys; spanning 2010-2013. Spatial autocorrelations were explored using Moran's I and hotspots were detected using flexible spatial scan statistics.
  
  
  RESULTS
  Seven hotspots of spatially clustered elevated vector density and eight of malaria infection prevalence were detected over both phases. Only a third of vectors were collected in hotspots in phase 1 (30 %) and phase 2 (33 %). Malaria prevalence hotspots accounted for only half of malaria infections detected in phase 1 (55 %) and phase 2 (47 %). Three quarters (76 % in phase 1 and 74 % in phase 2) of survey locations with detectable vector populations were outside of hotspots. Similarly, more than half of locations with higher infection prevalence (>10 %) occurred outside of hotspots (51 % in phase 1 and 54 % in phase 2). Vector proliferation hazard (exposure to An. gambiae) and malaria infection risk were only very loosely associated with each other (Odds ratio (OR) [95 % Confidence Interval (CI)] = 1.56 [0.89, 1.78], P = 0.52)).
  
  
  CONCLUSIONS
  Many small, scattered loci of local malaria transmission were haphazardly scattered across the city, so interventions targeting only currently identifiable spatially aggregated hotspots will have limited impact. Routine, spatially comprehensive, longitudinal entomological and parasitological surveillance systems, with sufficient sensitivity and spatial resolution to detect these scattered loci, are required to eliminate transmission from this typical African city. Intervention packages targeted to both loci and hotspots of transmission will need to suppress local vector proliferation, treat infected residents and provide vulnerable residents with supplementary protective measures against exposure.
authors.affiliation: School of Public Health, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa. vmwakalinga@ihi.or.tz.|Department of Housing and Infrastructure Planning, School of Urban and Regional Planning, Ardhi University, P.O. Box 35176, Dar es Salaam, United Republic of Tanzania. vmwakalinga@ihi.or.tz.|Environmental Health and Ecological Sciences Thematic Group, Ifakara Health Institute, Coordination Office, Kiko Avenue, Mikocheni, P.O. Box 78373, Dar es Salaam, United Republic of Tanzania. vmwakalinga@ihi.or.tz.
authors.forename: Victoria M
authors.initials: VM
authors.lastname: Mwakalinga
authors.affiliation: Discipline of Public Health Medicine, School of Nursing and Public Health, University of KwaZulu-Natal, Durban, South Africa. Sartorius@ukzn.ac.za.
authors.forename: Benn K D
authors.initials: BK
authors.lastname: Sartorius
authors.affiliation: Environmental Health and Ecological Sciences Thematic Group, Ifakara Health Institute, Coordination Office, Kiko Avenue, Mikocheni, P.O. Box 78373, Dar es Salaam, United Republic of Tanzania. ymlacha@ihi.or.tz.
authors.forename: Yeromin P
authors.initials: YP
authors.lastname: Mlacha
authors.affiliation: Environmental Health and Ecological Sciences Thematic Group, Ifakara Health Institute, Coordination Office, Kiko Avenue, Mikocheni, P.O. Box 78373, Dar es Salaam, United Republic of Tanzania. dmsellemu@ihi.or.tz.
authors.forename: Daniel F
authors.initials: DF
authors.lastname: Msellemu
authors.affiliation: Environmental Health and Ecological Sciences Thematic Group, Ifakara Health Institute, Coordination Office, Kiko Avenue, Mikocheni, P.O. Box 78373, Dar es Salaam, United Republic of Tanzania. alimwagu@ihi.or.tz.
authors.forename: Alex J
authors.initials: AJ
authors.lastname: Limwagu
authors.affiliation: Environmental Health and Ecological Sciences Thematic Group, Ifakara Health Institute, Coordination Office, Kiko Avenue, Mikocheni, P.O. Box 78373, Dar es Salaam, United Republic of Tanzania. zmageni@ihi.or.tz.
authors.forename: Zawadi D
authors.initials: ZD
authors.lastname: Mageni
authors.affiliation: Environmental Health and Ecological Sciences Thematic Group, Ifakara Health Institute, Coordination Office, Kiko Avenue, Mikocheni, P.O. Box 78373, Dar es Salaam, United Republic of Tanzania. jpaliga@ihi.or.tz.
authors.forename: John M
authors.initials: JM
authors.lastname: Paliga
authors.affiliation: Environmental Health and Ecological Sciences Thematic Group, Ifakara Health Institute, Coordination Office, Kiko Avenue, Mikocheni, P.O. Box 78373, Dar es Salaam, United Republic of Tanzania. govella@ihi.or.tz.
authors.forename: Nicodem J
authors.initials: NJ
authors.lastname: Govella
authors.affiliation: Wits Research Institute for Malaria, School of Pathology, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa. Maureen.Coetzee@wits.ac.za.
authors.forename: Maureen
authors.initials: M
authors.lastname: Coetzee
authors.affiliation: Environmental Health and Ecological Sciences Thematic Group, Ifakara Health Institute, Coordination Office, Kiko Avenue, Mikocheni, P.O. Box 78373, Dar es Salaam, United Republic of Tanzania. Gerry.Killeen@lstmed.ac.uk.|Vector Biology Department, Liverpool School of Tropical Medicine, Pembroke Place, Liverpool, L3 5QA, UK. Gerry.Killeen@lstmed.ac.uk.
authors.forename: Gerry F
authors.initials: GF
authors.lastname: Killeen
authors.affiliation: Environmental Health and Ecological Sciences Thematic Group, Ifakara Health Institute, Coordination Office, Kiko Avenue, Mikocheni, P.O. Box 78373, Dar es Salaam, United Republic of Tanzania. stefan.dongus@unibas.ch.|Vector Biology Department, Liverpool School of Tropical Medicine, Pembroke Place, Liverpool, L3 5QA, UK. stefan.dongus@unibas.ch.|Department of Epidemiology and Public Health, Swiss Tropical and Public Health Institute, P.O. Box, 4002, Basel, Switzerland. stefan.dongus@unibas.ch.|University of Basel, 4001, Basel, Switzerland. stefan.dongus@unibas.ch.
authors.forename: Stefan
authors.initials: S
authors.lastname: Dongus
mesh_terms: D000818:Animals; D000852:Anopheles / Q000502:physiology*; D016000:Cluster Analysis; D003430:Cross-Sectional Studies; D006801:Humans; D007303:Insect Vectors / Q000502:physiology*; D016778:Malaria, Falciparum / Q000453:epidemiology* / Q000635:transmission*; D010963:Plasmodium falciparum; D015995:Prevalence; D013636:Tanzania / Q000453:epidemiology