Burden of disease

Objectives:

To estimate the burden of malaria in Africa by combining empirical data of malaria prevalence and endemicity- related health outcomes with geographical data of population distribution and a malaria distribution model.

 

Methods:

This work is an extension of previous efforts to combine transmission risks, malaria mortality and population data for 1990 (Snow et al., 1999) with a refined effort at disease-risk and population stratification, a wider range of empirical data and a consideration of burdens other than mortality among the 1995 non-pregnant population of Africa.  

Based on the malaria distribution model (Craig et al., 1999) Africa was divided into zones of no risk (recognised potential of rare epidemics), stable and unstable transmission in sub-Saharan and southern Africa respectively (see figure). North African countries (Morocco, Western Sahara, Algeria, Tunisia, Libya and Egypt) were excluded. By overlaying a census- based model of population distribution (Deichmann, 1996) (see figure), the number of people of age groups 0-4, 5-9, 10-14 and 15 and older, living in the different risk zones, were computed. Through an extensive search of relevant empirical published and unpublished data, the average frequency of mortality, morbidity and sequelae under different epidemiological settings was determined. All this information was combined to estimate the burden of malaria in sub-Saharan Africa.

 

Results:

The following estimates were derived respectively for deaths and clinical attacks of malaria in 1995: in stable endemic malaria areas: 987 466 (incl. 765 442 children below five) and 207 million; in unstable transmission zones during an epidemic year: 128 241 and 13.3 million; in unstable zones under non-epidemic conditions: 1 500 and 150 000; in Southern Africa: 2 019 and 213 509. Additionally the risk and numbers of people with cerebral malaria, severe deficit, hemiparesis, visual impairment, epilepsy, hearing impairment, ataxia, speech disorder, severe malaria anaemia, and HIV contracted from blood transfusions for anaemia were computed. Between 200 and 800 disabling long-term events may have occurred among survivors of cerebral malaria in 1995, including only events likely to be life-long, thus the last decade may have witnessed a cohort of between 2000 and 8000 children who have been left with residual effects such as spasticity and epilepsy attributable to a brain insult caused by malaria. Furthermore an estimated 19,000 or more children aged 0-9 years, resident in the stable endemic areas of Africa may have survived blood transfusion for severe malaria anaemia, but would have acquired HIV as a result of receiving contaminated blood.

 

Conclusions:

These estimates of over 1 million deaths and over 200 million clinical events due to malaria in Africa in 1995 are well within those described for the sub-Saharan Africa by Murray and Lopez for the 1990 population and consistent with several previous claims before 1990. However, this approach provides a more rational basis for defining burden, which is transparent in its inputs, assumptions, limitations and caveats and allows for new evidence, empirically derived confidence limits and modelled predictions of change to be incorporated to derive new and better informed estimates in future.

 

Publications:

Snow, R. W., M. H. Craig, U. Deichmann, K. Marsh. 1999. Estimating mortality, morbidity and disability due to malaria among Africa's non-pregnant population. Bulletin of the World Health Organization 77:624-640.

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