title: Age, Spatial, and Temporal Variations in Hospital Admissions with Malaria in Kilifi County, Kenya: A 25-Year Longitudinal Observational Study.
abstract: BACKGROUND
  Encouraging progress has been seen with reductions in Plasmodium falciparum malaria transmission in some parts of Africa. Reduced transmission might lead to increasing susceptibility to malaria among older children due to lower acquired immunity, and this has implications for ongoing control strategies.
  
  
  RESULTS
  We conducted a longitudinal observational study of children admitted to Kilifi County Hospital in Kenya and linked it to data on residence and insecticide-treated net (ITN) use. This included data from 69,104 children aged from 3 mo to 13 y admitted to Kilifi County Hospital between 1 January 1990 and 31 December 2014. The variation in malaria slide positivity among admissions was examined in logistic regression models using the following predictors: location of the residence, calendar time, the child's age, ITN use, and the enhanced vegetation index (a proxy for soil moisture). The proportion of malaria slide-positive admissions declined from 0.56 (95% confidence interval [CI] 0.54-0.58) in 1998 to 0.07 (95% CI 0.06-0.08) in 2009 but then increased again through to 0.24 (95% CI 0.22-0.25) in 2014. Older children accounted for most of the increase after 2009 (0.035 [95% CI 0.030-0.040] among young children compared to 0.22 [95% CI 0.21-0.23] in older children). There was a nonlinear relationship between malaria risk and prevalence of ITN use within a 2 km radius of an admitted child's residence such that the predicted malaria positive fraction varied from ~0.4 to <0.1 as the prevalence of ITN use varied from 20% to 80%. In this observational analysis, we were unable to determine the cause of the decline in malaria between 1998 and 2009, which pre-dated the dramatic scale-up in ITN distribution and use.
  
  
  CONCLUSIONS
  Following a period of reduced transmission, a cohort of older children emerged who have increased susceptibility to malaria. Further reductions in malaria transmission are needed to mitigate the increasing burden among older children, and universal ITN coverage is a promising strategy to achieve this goal.
authors.affiliation: KEMRI-Wellcome Trust Research Programme, Kilifi, Kenya.
authors.forename: Polycarp
authors.initials: P
authors.lastname: Mogeni
authors.affiliation: KEMRI-Wellcome Trust Research Programme, Kilifi, Kenya.|Imperial College London, London, United Kingdom.
authors.forename: Thomas N
authors.initials: TN
authors.lastname: Williams
authors.affiliation: KEMRI-Wellcome Trust Research Programme, Kilifi, Kenya.|Centre for Tropical Medicine and Global Health, Nuffield Department of Clinical Medicine, University of Oxford, CCVTM, Oxford, United Kingdom.
authors.forename: Gregory
authors.identifier: http://orcid.org/0000-0002-2663-2765
authors.initials: G
authors.lastname: Fegan
authors.affiliation: KEMRI-Wellcome Trust Research Programme, Kilifi, Kenya.
authors.forename: Christopher
authors.initials: C
authors.lastname: Nyundo
authors.affiliation: KEMRI-Wellcome Trust Research Programme, Kilifi, Kenya.
authors.forename: Evasius
authors.initials: E
authors.lastname: Bauni
authors.affiliation: KEMRI-Wellcome Trust Research Programme, Kilifi, Kenya.
authors.forename: Kennedy
authors.identifier: http://orcid.org/0000-0002-7757-7516
authors.initials: K
authors.lastname: Mwai
authors.affiliation: KEMRI-Wellcome Trust Research Programme, Kilifi, Kenya.
authors.forename: Irene
authors.initials: I
authors.lastname: Omedo
authors.affiliation: KEMRI-Wellcome Trust Research Programme, Kilifi, Kenya.
authors.forename: Patricia
authors.initials: P
authors.lastname: Njuguna
authors.affiliation: KEMRI-Wellcome Trust Research Programme, Kilifi, Kenya.|Centre for Tropical Medicine and Global Health, Nuffield Department of Clinical Medicine, University of Oxford, CCVTM, Oxford, United Kingdom.
authors.forename: Charles R
authors.initials: CR
authors.lastname: Newton
authors.affiliation: KEMRI-Wellcome Trust Research Programme, Kilifi, Kenya.
authors.forename: Faith
authors.initials: F
authors.lastname: Osier
authors.affiliation: KEMRI-Wellcome Trust Research Programme, Kilifi, Kenya.|Centre for Tropical Medicine and Global Health, Nuffield Department of Clinical Medicine, University of Oxford, CCVTM, Oxford, United Kingdom.
authors.forename: James A
authors.initials: JA
authors.lastname: Berkley
authors.affiliation: KEMRI-Wellcome Trust Research Programme, Kilifi, Kenya.|Johns Hopkins Bloomberg School of Public Health, Department of International Health, Baltimore, Maryland, United States of America.
authors.forename: Laura L
authors.initials: LL
authors.lastname: Hammitt
authors.affiliation: KEMRI-Wellcome Trust Research Programme, Kilifi, Kenya.
authors.forename: Brett
authors.identifier: http://orcid.org/0000-0002-4422-8627
authors.initials: B
authors.lastname: Lowe
authors.affiliation: KEMRI-Wellcome Trust Research Programme, Kilifi, Kenya.
authors.forename: Gabriel
authors.identifier: http://orcid.org/0000-0002-9276-8759
authors.initials: G
authors.lastname: Mwambingu
authors.affiliation: KEMRI-Wellcome Trust Research Programme, Kilifi, Kenya.
authors.forename: Ken
authors.initials: K
authors.lastname: Awuondo
authors.affiliation: KEMRI-Wellcome Trust Research Programme, Kilifi, Kenya.
authors.forename: Neema
authors.initials: N
authors.lastname: Mturi
authors.affiliation: KEMRI-Wellcome Trust Research Programme, Kilifi, Kenya.
authors.forename: Norbert
authors.identifier: http://orcid.org/0000-0002-8038-3894
authors.initials: N
authors.lastname: Peshu
authors.affiliation: Centre for Tropical Medicine and Global Health, Nuffield Department of Clinical Medicine, University of Oxford, CCVTM, Oxford, United Kingdom.|Spatial Health Metrics Group, Kenya Medical Research Institute/Wellcome Trust Research Programme, Nairobi, Kenya.
authors.forename: Robert W
authors.initials: RW
authors.lastname: Snow
authors.affiliation: Centre for Tropical Medicine and Global Health, Nuffield Department of Clinical Medicine, University of Oxford, CCVTM, Oxford, United Kingdom.|Spatial Health Metrics Group, Kenya Medical Research Institute/Wellcome Trust Research Programme, Nairobi, Kenya.
authors.forename: Abdisalan
authors.initials: A
authors.lastname: Noor
authors.affiliation: KEMRI-Wellcome Trust Research Programme, Kilifi, Kenya.|Centre for Tropical Medicine and Global Health, Nuffield Department of Clinical Medicine, University of Oxford, CCVTM, Oxford, United Kingdom.
authors.forename: Kevin
authors.initials: K
authors.lastname: Marsh
authors.affiliation: KEMRI-Wellcome Trust Research Programme, Kilifi, Kenya.|Centre for Tropical Medicine and Global Health, Nuffield Department of Clinical Medicine, University of Oxford, CCVTM, Oxford, United Kingdom.
authors.forename: Philip
authors.initials: P
authors.lastname: Bejon
mesh_terms: D000293:Adolescent; D002648:Child; D002675:Child, Preschool; D005260:Female; D006760:Hospitalization / Q000706:statistics & numerical data* / Q000639:trends; D006801:Humans; D007223:Infant; D057148:Insecticide-Treated Bednets / Q000706:statistics & numerical data*; D007630:Kenya / Q000453:epidemiology; D008137:Longitudinal Studies; D008288:Malaria / Q000453:epidemiology* / Q000469:parasitology; D008297:Male; D009032:Mosquito Control / Q000706:statistics & numerical data; D015995:Prevalence; D012306:Risk