Models for short term malaria prediction in Sri Lanka

Olivier JT Briët¹^,2 , Penelope Vounatsou² , Dissanayake M Gunawardena³ , Gawrie NL Galappaththy⁴ and Priyanie H Amerasinghe⁵

¹International Water Management Institute, P.O. Box 2075, Colombo, Sri Lanka

²Swiss Tropical Institute, Socinstrasse 57, P.O. Box CH-4002, Basel, Switzerland

³US Agency for International Development, P.O. Box 7856, Kampala, Uganda

⁴Anti Malaria Campaign, Head Office Colombo, Sri Lanka

⁵International Water Management Institute Sub Regional Office for South Asia, c/o ICRISAT, Patancheru, AP 502 324, Andhra Pradesh, India

author email corresponding author email

Malaria Journal 2008, 7:76doi:10.1186/1475-2875-7-76


Published:	6 May 2008

Abstract

Background

Malaria in Sri Lanka is unstable and fluctuates in intensity both spatially and temporally. Although the case counts are dwindling at present, given the past history of resurgence of outbreaks despite effective control measures, the control programmes have to stay prepared. The availability of long time series of monitored/diagnosed malaria cases allows for the study of forecasting models, with an aim to developing a forecasting system which could assist in the efficient allocation of resources for malaria control.

Methods

Exponentially weighted moving average models, autoregressive integrated moving average (ARIMA) models with seasonal components, and seasonal multiplicative autoregressive integrated moving average (SARIMA) models were compared on monthly time series of district malaria cases for their ability to predict the number of malaria cases one to four months ahead. The addition of covariates such as the number of malaria cases in neighbouring districts or rainfall were assessed for their ability to improve prediction of selected (seasonal) ARIMA models.

Results

The best model for forecasting and the forecasting error varied strongly among the districts. The addition of rainfall as a covariate improved prediction of selected (seasonal) ARIMA models modestly in some districts but worsened prediction in other districts. Improvement by adding rainfall was more frequent at larger forecasting horizons.

Conclusion

Heterogeneity of patterns of malaria in Sri Lanka requires regionally specific prediction models. Prediction error was large at a minimum of 22% (for one of the districts) for one month ahead predictions. The modest improvement made in short term prediction by adding rainfall as a covariate to these prediction models may not be sufficient to merit investing in a forecasting system for which rainfall data are routinely processed.