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. 2010 Feb 24:9:59.
doi: 10.1186/1475-2875-9-59.

High heterogeneity in Plasmodium falciparum risk illustrates the need for detailed mapping to guide resource allocation: a new malaria risk map of the Lao People's Democratic Republic

Pernille Jorgensen, Simone Nambanya, Deyer Gopinath, Bouasy Hongvanthong, Kongxay Luangphengsouk, David Bell, Samlane Phompida, Rattanaxay Phetsouvanh

High heterogeneity in Plasmodium falciparum risk illustrates the need for detailed mapping to guide resource allocation: a new malaria risk map of the Lao People's Democratic Republic

Pernille Jorgensen et al. Malar J. .

Abstract

Background: Accurate information on the geographical distribution of malaria is important for efficient resource allocation. The Lao People's Democratic Republic has experienced a major decline in malaria morbidity and mortality in the past decade. However, efforts to respond effectively to these changes have been impeded by lack of detailed data on malaria distribution. In 2008, a countrywide survey on Plasmodium falciparum diagnosed in health centres and villages was initiated to develop a detailed P. falciparum risk map with the aim to identify priority areas for malaria control, estimate population at risk, and guide resource allocation in the Lao People's Democratic Republic.

Methods: P. falciparum incidence data were collected from point-referenced villages and health centres for the period 2006-2008 during a country-wide survey between December 2008 and January 2009. Using the highest recorded annual rate, continuous surfaces of P. falciparum incidence were produced by the inverse distance weighted interpolation technique.

Results: Incidence rates were obtained from 3,876 villages and 685 health centres. The risk map shows that P. falciparum is highly heterogeneous in the northern and central regions of the country with large areas of no transmission. In the southern part, transmission is pervasive and the risk of P. falciparum is high. It was estimated that 3.4 million people (60% of the population) live at risk of malaria.

Conclusions: This paper presents the first comprehensive malaria risk map of the Lao People's Democratic Republic based entirely on empirical data. The estimated population at risk is substantially lower than previous estimates, reflecting the presence of vast areas with focal or no malaria transmission as identified in this study. These findings provide important guidance for malaria control interventions in the Lao People's Democratic Republic, and underline the need for detailed data on malaria to accurately predict risk in countries with heterogeneous transmission.

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Figures

Figure 1
Figure 1
Distribution of P. falciparum cases diagnosed by health centres and villages included in the survey. Red dots: Villages or health centres reporting at least one confirmed case of P. falciparum between 2006 and 2008, green dots: Villages or health centres which did not confirm any case of P. falciparum between 2006 and 2008. Grey areas signify unpopulated areas (areas >10 km from a village centre).
Figure 2
Figure 2
Proportion (%) of villages recording at least 1 confirmed case of P. falciparum among all villages with RDTs between 2006 and 2008 by province and region (number of villages = 3,876).
Figure 3
Figure 3
Interpolated highest annual incidence rates of P. falciparum based on data from 3,876 villages and 685 health centres (2006-2008). Black dots show villages not included in the survey for which estimates on incidence were not available. Northern provinces: Phongsaly, Luangnamtha, Luangprabang, Bokeo, and Oudomxay; Central provinces: Huaphan, Xiengkhuang, Vientiane, Vientiane Capital, Xaignabury, and Bolikhamxay; and Southern provinces: Khammuane, Savannakhet, Saravane, Sekong, Champasack, and Attapeu.
Figure 4
Figure 4
Map showing total number of confirmed P. falciparum cases recorded by district hospitals in 2008 in five central provinces of Lao PDR.
Figure 5
Figure 5
Estimated population at risk of P. falciparum in Lao PDR by interpolated incidence rate group (population data from 2005 census).
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