Stable and unstable malaria hotspots in longitudinal cohort studies in Kenya.

<h4>Background</h4>Infectious diseases often demonstrate heterogeneity of transmission among host populations. This heterogeneity reduces the efficacy of control strategies, but also implies that focusing control strategies on "hotspots" of transmission could be highly effectiv...

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Autores principales:	Philip Bejon, Thomas N Williams, Anne Liljander, Abdisalan M Noor, Juliana Wambua, Edna Ogada, Ally Olotu, Faith H A Osier, Simon I Hay, Anna Färnert, Kevin Marsh
Formato:	article
Lenguaje:	EN
Publicado:	Public Library of Science (PLoS) 2010
Materias:	Medicine R
Acceso en línea:	https://doaj.org/article/6784a10e6a1e4030a6dc307c291beb26
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spelling	oai:doaj.org-article:6784a10e6a1e4030a6dc307c291beb262021-12-02T19:56:09ZStable and unstable malaria hotspots in longitudinal cohort studies in Kenya.1549-12771549-167610.1371/journal.pmed.1000304https://doaj.org/article/6784a10e6a1e4030a6dc307c291beb262010-07-01T00:00:00Zhttps://www.ncbi.nlm.nih.gov/pmc/articles/pmid/20625549/?tool=EBIhttps://doaj.org/toc/1549-1277https://doaj.org/toc/1549-1676<h4>Background</h4>Infectious diseases often demonstrate heterogeneity of transmission among host populations. This heterogeneity reduces the efficacy of control strategies, but also implies that focusing control strategies on "hotspots" of transmission could be highly effective.<h4>Methods and findings</h4>In order to identify hotspots of malaria transmission, we analysed longitudinal data on febrile malaria episodes, asymptomatic parasitaemia, and antibody titres over 12 y from 256 homesteads in three study areas in Kilifi District on the Kenyan coast. We examined heterogeneity by homestead, and identified groups of homesteads that formed hotspots using a spatial scan statistic. Two types of statistically significant hotspots were detected; stable hotspots of asymptomatic parasitaemia and unstable hotspots of febrile malaria. The stable hotspots were associated with higher average AMA-1 antibody titres than the unstable clusters (optical density [OD] = 1.24, 95% confidence interval [CI] 1.02-1.47 versus OD = 1.1, 95% CI 0.88-1.33) and lower mean ages of febrile malaria episodes (5.8 y, 95% CI 5.6-6.0 versus 5.91 y, 95% CI 5.7-6.1). A falling gradient of febrile malaria incidence was identified in the penumbrae of both hotspots. Hotspots were associated with AMA-1 titres, but not seroconversion rates. In order to target control measures, homesteads at risk of febrile malaria could be predicted by identifying the 20% of homesteads that experienced an episode of febrile malaria during one month in the dry season. That 20% subsequently experienced 65% of all febrile malaria episodes during the following year. A definition based on remote sensing data was 81% sensitive and 63% specific for the stable hotspots of asymptomatic malaria.<h4>Conclusions</h4>Hotspots of asymptomatic parasitaemia are stable over time, but hotspots of febrile malaria are unstable. This finding may be because immunity offsets the high rate of febrile malaria that might otherwise result in stable hotspots, whereas unstable hotspots necessarily affect a population with less prior exposure to malaria.Philip BejonThomas N WilliamsAnne LiljanderAbdisalan M NoorJuliana WambuaEdna OgadaAlly OlotuFaith H A OsierSimon I HayAnna FärnertKevin MarshPublic Library of Science (PLoS)articleMedicineRENPLoS Medicine, Vol 7, Iss 7, p e1000304 (2010)
institution	DOAJ
collection	DOAJ
language	EN
topic	Medicine R
spellingShingle	Medicine R Philip Bejon Thomas N Williams Anne Liljander Abdisalan M Noor Juliana Wambua Edna Ogada Ally Olotu Faith H A Osier Simon I Hay Anna Färnert Kevin Marsh Stable and unstable malaria hotspots in longitudinal cohort studies in Kenya.
description	<h4>Background</h4>Infectious diseases often demonstrate heterogeneity of transmission among host populations. This heterogeneity reduces the efficacy of control strategies, but also implies that focusing control strategies on "hotspots" of transmission could be highly effective.<h4>Methods and findings</h4>In order to identify hotspots of malaria transmission, we analysed longitudinal data on febrile malaria episodes, asymptomatic parasitaemia, and antibody titres over 12 y from 256 homesteads in three study areas in Kilifi District on the Kenyan coast. We examined heterogeneity by homestead, and identified groups of homesteads that formed hotspots using a spatial scan statistic. Two types of statistically significant hotspots were detected; stable hotspots of asymptomatic parasitaemia and unstable hotspots of febrile malaria. The stable hotspots were associated with higher average AMA-1 antibody titres than the unstable clusters (optical density [OD] = 1.24, 95% confidence interval [CI] 1.02-1.47 versus OD = 1.1, 95% CI 0.88-1.33) and lower mean ages of febrile malaria episodes (5.8 y, 95% CI 5.6-6.0 versus 5.91 y, 95% CI 5.7-6.1). A falling gradient of febrile malaria incidence was identified in the penumbrae of both hotspots. Hotspots were associated with AMA-1 titres, but not seroconversion rates. In order to target control measures, homesteads at risk of febrile malaria could be predicted by identifying the 20% of homesteads that experienced an episode of febrile malaria during one month in the dry season. That 20% subsequently experienced 65% of all febrile malaria episodes during the following year. A definition based on remote sensing data was 81% sensitive and 63% specific for the stable hotspots of asymptomatic malaria.<h4>Conclusions</h4>Hotspots of asymptomatic parasitaemia are stable over time, but hotspots of febrile malaria are unstable. This finding may be because immunity offsets the high rate of febrile malaria that might otherwise result in stable hotspots, whereas unstable hotspots necessarily affect a population with less prior exposure to malaria.
format	article
author	Philip Bejon Thomas N Williams Anne Liljander Abdisalan M Noor Juliana Wambua Edna Ogada Ally Olotu Faith H A Osier Simon I Hay Anna Färnert Kevin Marsh
author_facet	Philip Bejon Thomas N Williams Anne Liljander Abdisalan M Noor Juliana Wambua Edna Ogada Ally Olotu Faith H A Osier Simon I Hay Anna Färnert Kevin Marsh
author_sort	Philip Bejon
title	Stable and unstable malaria hotspots in longitudinal cohort studies in Kenya.
title_short	Stable and unstable malaria hotspots in longitudinal cohort studies in Kenya.
title_full	Stable and unstable malaria hotspots in longitudinal cohort studies in Kenya.
title_fullStr	Stable and unstable malaria hotspots in longitudinal cohort studies in Kenya.
title_full_unstemmed	Stable and unstable malaria hotspots in longitudinal cohort studies in Kenya.
title_sort	stable and unstable malaria hotspots in longitudinal cohort studies in kenya.
publisher	Public Library of Science (PLoS)
publishDate	2010
url	https://doaj.org/article/6784a10e6a1e4030a6dc307c291beb26
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Stable and unstable malaria hotspots in longitudinal cohort studies in Kenya.

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