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Open Access Highly Accessed Research

Spatio-temporal malaria transmission patterns in Navrongo demographic surveillance site, northern Ghana

Simon Kasasa123, Victor Asoala4, Laura Gosoniu12, Francis Anto5, Martin Adjuik6, Cletus Tindana4, Thomas Smith12, Seth Owusu-Agyei7 and Penelope Vounatsou12*

Author Affiliations

1 Swiss Tropical and Public Health Institute, Socinstrasse 57, P.O. Box 4002, Basel, Switzerland

2 University of Basel, Basel, Switzerland

3 School of Public Health, Makerere University College of Health Sciences, Kampala, Uganda

4 Navrongo Health Research Centre, Navrongo, Ghana

5 School of Public Health, University of Ghana, Legon, Ghana

6 INDEPTH Network Secretariat, Accra, Ghana

7 Kintampo Health Research Centre, Ghana Health Services, Ministry of Health, Kintampo, Ghana

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Malaria Journal 2013, 12:63  doi:10.1186/1475-2875-12-63

Published: 13 February 2013

Abstract

Background

The relationship between entomological measures of malaria transmission intensity and mortality remains uncertain. This is partly because transmission is heterogeneous even within small geographical areas. Studying this relationship requires high resolution, spatially structured, longitudinal entomological data. Geostatistical models that have been used to analyse the spatio-temporal heterogeneity have not considered the uncertainty in both sporozoite rate (SR) and mosquito density data. This study analysed data from Kassena-Nankana districts in northern Ghana to obtain small area estimates of malaria transmission rates allowing for this uncertainty.

Methods

Independent Bayesian geostatistical models for sporozoite rate and mosquito density were fitted to produce explicit entomological inoculation rate (EIR) estimates for small areas and short time periods, controlling for environmental factors.

Results

Mosquitoes were trapped from 2,803 unique locations for three years using mainly CDC light traps. Anopheles gambiae constituted 52%, the rest were Anopheles funestus. Mean biting rates for An. funestus and An. gambiae were 32 and 33 respectively. Most bites occurred in September, the wettest month. The sporozoite rates were higher in the dry periods of the last two years compared with the wet period. The annual EIR varied from 1,132 to 157 infective bites. Monthly EIR varied between zero and 388 infective bites. Spatial correlation for SR was lower than that of mosquito densities.

Conclusion

This study confirms the presence of spatio-temporal heterogeneity in malaria transmission within a small geographical area. Spatial variance was stronger than temporal especially in the SR. The estimated EIR will be used in mortality analysis for the area.

Keywords:
Entomological inoculation rate; Spatio-temporal; Zero-inflated; Malaria; Malaria Transmission Intensity and Mortality Burden Across Africa (MTIMBA) project