• 1

    Snow RW, Omumbo JA, Lowe B, Molyneux CS, Obiero JO, Palmer A, Weber MW, Pinder M, Nahlen B, Obonyo C, New-bold C, Gupta S, Marsh K, 1997. Relation between severe malaria morbidity in children and level of Plasmodium falciparum transmission in Africa. Lancet 349 :1650–1654.

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  • 2

    Trape JF, Quinet MC, Nzingoula S, Senga P, Tchichelle F, Carme B, Candito D, Mayanda H, Zoulani A, 1987. Malaria and urbanization in Central Africa—the example of Brazzaville. 5. Pernicious attacks and mortality. Trans R Soc Trop Med Hyg 81 :34–42.

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  • 3

    Snow RW, Deazevedo IB, Lowe BS, Kabiru EW, Nevill CG, Mwankusye S, Kassiga G, Marsh B, Teuscher T, 1994. Severe childhood malaria in 2 areas of markedly different falciparum transmission in East Africa. Acta Trop 57 :289–300.

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  • 4

    Marsh K, Snow RW, 1999. Malaria transmission and morbidity. Parassitologia 41 :241–246.

  • 5

    Smith T, Killeen G, Lengeler C, Tanner M, 2004. Relationships between the outcome of Plasmodium falciparum infection and the intensity of transmission in Africa. Am J Trop Med Hyg 71 :80–86.

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  • 6

    Smith TA, Leuenberger R, Lengeler C, 2001. Child mortality and malaria transmission intensity in Africa. Trends Parasitol 17 :145–149.

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    Snow RW, Marsh K, 1995. Will reducing Plasmodium falciparum transmission alter malaria mortality among African children? Parasitol Today 11 :188–190.

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  • 8

    Reyburn H, Mbatia R, Drakeley C, Bruce J, Carneiro I, Olomi R, Cox J, Nkya W, Lemnge M, Greenwood BM, Riley EM, 2005. Association of transmission intensity and age with clinical manifestations and case fatality of severe Plasmodium falciparum malaria. JAMA 293 :1461–1470.

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  • 9

    Idro R, Aloyo J, Mayende L, Bitarakwate E, John CC, Kivumbi GW, 2006. Severe malaria in children in areas with low, moderate and high transmission intensity in Uganda. Trop Med Int Health 11 :115–124.

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  • 10

    Modiano D, Sirima BS, Sawadogo A, Sanou I, Pare J, Konate A, Pagnoni F, 1998. Severe malaria in Burkina Faso: influence of age and transmission level on clinical presentation. Am J Trop Med Hyg 59 :539–542.

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    Baird JK, Basri H, Weina P, MaGuire JD, Barcus MJ, Picarema H, Elyazar IR, Ayomi E, Sekartuti, 2003. Adult Javanese migrants to Indonesian Papua at high risk of severe disease caused by malaria. Epidemiol Infect 131 :791–797.

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    Smith T, Charlwood JD, Kitua AY, Masanja H, Mwankusye S, Alonso PL, Tanner M, 1998. Relationships of malaria morbidity with exposure to Plasmodium falciparum in young children in a highly endemic area. Am J Trop Med Hyg 59 :252–257.

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  • 14

    Snow RW, Schellenberg J, Peshu N, Forster D, Newton C, Winstanley PA, Mwangi I, Waruiru C, Warn PA, Newbold C, Marsh K, 1993. Periodicity and space-time clustering of severe childhood malaria on the coast of Kenya. Trans R Soc Trop Med Hyg 87 :386–390.

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  • 15

    Mwangi TW, Ross A, Snow RW, Marsh K, 2005. Case definitions of clinical malaria under different transmission conditions in Kilifi District, Kenya. J Infect Dis 191 :1932–1939.

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  • 16

    Mbogo CNM, Snow RW, Khamala CPM, Kabiru EW, Ouma JH, Githure JI, Marsh K, Beier JC, 1995. Relationships between Plasmodium falciparum transmission by vector populations and the incidence of severe disease at 9 sites on the Kenyan coast. Am J Trop Med Hyg 52 :201–206.

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  • 17

    Mbogo CM, Mwangangi JM, Nzovu J, Gu WD, Yan GY, Gunter JT, Swalm C, Keating J, Regens JL, Shililu JI, Githure JI, Beier JC, 2003. Spatial and temporal heterogeneity of anopheles mosquitoes and Plasmodium falciparum transmission along the Kenyan coast. Am J Trop Med Hyg 68 :734–742.

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  • 18

    Snow RW, Peshu N, Forster D, Mwenesi H, Marsh K, 1992. The role of shops in the treatment and prevention of childhood malaria on the coast of Kenya. Trans R Soc Trop Med Hyg 86 :237–239.

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  • 19

    Nevill CG, Some ES, Mungala VO, Mutemi W, New L, Marsh K, Lengeler C, Snow RW, 1996. Insecticide-treated bednets reduce mortality and severe morbidity from malaria among children on the Kenyan coast. Trop Med Int Health 1 :139–146.

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  • 20

    Snow RW, McCabe E, Mbogo CNM, Molyneux CS, Some ES, Mung’ala V, Nevill CG, 1999. The effect of delivery mechanisms on the uptake of bed net re-impregnation in Kilifi District, Kenya. Health Policy Plan 14 :18–25.

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  • 21

    Mwangi TW, Ross A, Marsh K, Snow RW, 2003. The effects of untreated bednets on malaria infection and morbidity on the Kenyan coast. Trans R Soc Trop Med Hyg 97 :369–372.

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  • 22

    Noor AM, Amin AA, Akhwale WS, Snow RW, 2007. Increasing coverage and decreasing inequity in insecticide-treated bed net use among rural Kenyan children. Plos Medicine 4 :1341–1348.

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  • 23

    Okiro EA, Hay SI, Gikandi PW, Sharif SK, Noor AM, Peshu N, Marsh K, Snow RW, 2007. The decline in paediatric malaria admissions on the coast of Kenya. Malar J 6 :151.

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  • 24

    Shretta R, Omumbo J, Rapuoda B, Snow RW, 2000. Using evidence to change antimalarial drug policy in Kenya. Trop Med Int Health 5 :755–764.

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  • 25

    Marsh VM, Mutemi WM, Willetts A, Bayah K, Were S, Ross A, Marsh K, 2004. Improving malaria home treatment by training drug retailers in rural Kenya. Trop Med Int Health 9 :451–460.

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  • 26

    Amin AA, Zurovac D, Kangwana BB, Greenfield J, Otieno DN, Akhwale WS, Snow RW, 2007. The challenges of changing national malaria drug policy to artemisinin-based combinations in Kenya. Malar J 6 :72.

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  • 27

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  • 28

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  • 29

    Bejon P, Berkley JA, Mwangi T, Ogada E, Mwangi I, Maitland K, Williams T, Scott JA, English M, Lowe BS, Peshu N, Newton CR, Marsh K, 2007. Defining childhood severe falciparum malaria for intervention studies. PLoS Med 4 :e251.

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  • 30

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    Snow RW, Molyneux CS, Warn PA, Omumbo J, Nevill CG, Gupta S, Marsh K, 1996. Infant parasite rates and immunoglobulin in seroprevalence as a measure of exposure to Plasmodium falciparum during a randomized controlled trial of insecticide-treated bed nets on the Kenyan coast. Am J Trop Med Hyg 55 :144–149.

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  • 32

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  • 33

    Mbogo CNM, Snow RW, Kabiru EW, Ouma JH, Githure JI, Marsh K, Beier JC, 1993. Low-level Plasmodium falciparum transmssion and the incidence of severe malaria infections on the Kenyan coast. Am J Trop Med Hyg 49 :245–253.

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  • 34

    Rogier C, Tall A, Diagne N, Fontenille D, Spiegel A, Trape JF, 1999. Plasmodium falciparum clinical malaria: lessons from longitudinal studies in Senegal. Parassitologia 41 :255–259.

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  • 35

    Schellenberg D, Menendez C, Aponte J, Guinovart C, Mshinda H, Tanner M, Alonso P, 2004. The changing epidemiology of malaria in Ifakara Town, southern Tanzania. Trop Med Int Health 9 :68–76.

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Relationship Between Exposure, Clinical Malaria, and Age in an Area of Changing Transmission Intensity

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  • 1 Fogarty International Center, National Institutes of Health, Bethesda, Maryland; Kenya Medical Research Institute, CGMRC/Wellcome Trust Collaborative Programme, Kilifi, Kenya; KEMRI/Wellcome Trust Collaborative Programme, Nairobi, Kenya; Centre of Tropical Medicine, Nuffield Department of Clinical Medicine, University of Oxford, John Radcliffe Hospital, Headington, Oxford, United Kingdom
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The relationship between malaria transmission intensity and clinical disease is important for predicting the outcome of control measures that reduce transmission. Comparisons of hospital data between areas of differing transmission intensity suggest that the mean age of hospitalized clinical malaria is higher under relatively lower transmission, but the total number of episodes is similar until transmission drops below a threshold, where the risks of hospitalized malaria decline. These observations have rarely been examined longitudinally in a single community where transmission declines over time. We reconstructed 16 years (1991–2006) of pediatric hospital surveillance data and infection prevalence surveys from a circumscribed geographic area on the Kenyan coast. The incidence of clinical malaria remained high, despite sustained reductions in exposure to infection. However, the age group experiencing the clinical attacks of malaria increased steadily as exposure declined and may precede changes in the number of episodes in an area with declining transmission.

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