Research

Space-time variation of malaria incidence in Yunnan province, China

Archie CA Clements^1,2 , Adrian G Barnett³ , Zhang Wei Cheng⁴ , Robert W Snow^5,6 and Hom Ning Zhou⁴

¹  University of Queensland, School of Population Health, Herston, Queensland, Australia

²  Australian Centre for International and Tropical Health, Queensland Institute of Medical Research, Herston, Queensland, Australia

³  Institute of Health and Biomedical Innovation, Queensland University of Technology, Kelvin Grove, Queensland, Australia

⁴  Yunnan Institute of Parasitic Diseases, Pu'er, Yunnan, PR China

⁵  Malaria Public Health and Epidemiology Group, Centre for Geographic Medicine, KEMRI – University of Oxford – Wellcome Trust Collaborative Programme, Nairobi, Kenya

⁶  Centre for Tropical Medicine, Nuffield Department of Clinical Medicine, University of Oxford, CCVTM, Oxford, UK

author email corresponding author email

Malaria Journal 2009, 8:180doi:10.1186/1475-2875-8-180

Published:	31 July 2009

Abstract

Background

Understanding spatio-temporal variation in malaria incidence provides a basis for effective disease control planning and monitoring.

Methods

Monthly surveillance data between 1991 and 2006 for Plasmodium vivax and Plasmodium falciparum malaria across 128 counties were assembled for Yunnan, a province of China with one of the highest burdens of malaria. County-level Bayesian Poisson regression models of incidence were constructed, with effects for rainfall, maximum temperature and temporal trend. The model also allowed for spatial variation in county-level incidence and temporal trend, and dependence between incidence in June–September and the preceding January–February.

Results

Models revealed strong associations between malaria incidence and both rainfall and maximum temperature. There was a significant association between incidence in June–September and the preceding January–February. Raw standardised morbidity ratios showed a high incidence in some counties bordering Myanmar, Laos and Vietnam, and counties in the Red River valley. Clusters of counties in south-western and northern Yunnan were identified that had high incidence not explained by climate. The overall trend in incidence decreased, but there was significant variation between counties.

Conclusion

Dependence between incidence in summer and the preceding January–February suggests a role of intrinsic host-pathogen dynamics. Incidence during the summer peak might be predictable based on incidence in January–February, facilitating malaria control planning, scaled months in advance to the magnitude of the summer malaria burden. Heterogeneities in county-level temporal trends suggest that reductions in the burden of malaria have been unevenly distributed throughout the province.