Linking malaria in Limpopo province, South Africa to climate using self-organizing maps

Abstract

Introduction-Global malaria cases have drastically dropped in recent years, however there is still high incidence in sub-Saharan African countries. South Africa is mostly malaria-free, but northeastern provinces still have seasonal transmission of malaria. Past studies have reported various relationships between malaria and climatic factors. The aim of this study is to investigate patterns in malaria incidence in Limpopo and explore the association to climate conditions. Methods-Self-organizing maps were used to find patterns in malaria incidence based on case data. Composite analysis showed different climate patterns that associated to high and low incidence events. Classification methods were used to predict future malaria incidence. Results-Strong association of high malaria incidence to climate were found at varying lags. Interestingly significant association was seen with the rainfall of neighboring Mozambique at 2- to 4-months lag, as well as strong easterly winds over Mozambique Channel at 2-month lag, and drier conditions in Limpopo at 0- and 1-month lag. These provided optimal conditions for malaria incidence to reach higher rates during spring and lasting for consecutive seasons. Composite maps of sea surface temperature showed La Nina patterns in the tropical Pacific, which cause higher than normal rainfall over southern Africa. In contrast, seasons with low incidence were associated with considerably drier conditions at 2-month lag, and more westerly winds over southern Africa. Classification methods predicted events of high and low malaria incidence several months in advance. Conclusion-Links of malaria incidence to lagged climate patterns of temperatures in Limpopo, rainfall in Mozambique, zonal winds over the Mozambique Channel, and La Nina events suggest the importance of local climate as well as that of neighboring countries. This implies that there is a need for strengthening cross-border malaria control management to minimize the spread of malaria.