Mortality rates in sub-Saharan Africa (SSA) remain very high, especially when compared to other regions of the world 12. While mortality in many parts of the world has declined markedly in the last century, in SSA reductions have been less, although marked differences in trends between urban and rural areas are still observed with trends declining faster in urban areas 1345. A recent report from the World Health Organization estimates that each year there are about ten million deaths worldwide in children below five years of age 1. The leading causes of death among children in this age-group are pneumonia, diarrhoea, malaria, and perinatal causes.

Approximately 90% of all malaria deaths in the world occur in Africa 16. Major factors that contribute to this high mortality from malaria in Africa include poor access to health services, low quality of health services, and the increased resistance of malaria parasites to affordable first-line drugs such as chloroquine and sulphadoxine-pyrimethamine 78. There is some evidence for a positive correlation between Plasmodium falciparum transmission intensity and malaria mortality but there are few data on this point and also such analysis is hampered by the difficulties in assessing causes of death 91011. Moreover, in regions where malaria is endemic, an association between observed all-cause mortality rates and malaria-specific mortality rates, especially among the children below five years of age would be expected. However, it is difficult to substantiate this association due to the scarcity of quality data from Africa on all-cause and in particular cause-specific mortality. Many surveys and a few censuses have been conducted in Africa since the early 1950s and these provide information on all-cause mortality rate but not on cause-specific mortality 12. To address this gap, several demographic surveillance systems (DSS) have been established in developing countries where overall mortality, cause-specific mortality determined using the post-mortem questionnaire technique, morbidity, socio-economic status and migration can be studied 13.

In this study, data from surveys and censuses, as well as DSS data obtained from The Gambia and Burkina Faso were used to systematically compare all-cause and cause-specific mortality rates from under five children. Burkina Faso has four DSS sites located in Nouna, Ouagadougou, Oubritenga and Sapone, while Gambia has one in Farafenni 14. The climate of both countries is similar with a short and intense rainy season occurring between June and October. Malaria transmission intensity is generally more marked in Burkina Faso15, than in The Gambia 16.

A literature search was done on papers containing information on mortality and malaria among children below five years of age from each country for the years since 1950. The online search was done in Medline, Embase, and Popline, using key words: "Africa, child deaths, The Gambia, Burkina Faso, malaria, Plasmodium falciparum, mortality, child survival and morbidity". Subsequent literature searches were accomplished by reviewing the literature cited in each of the publications obtained. In addition, research groups and experts with publications related to studies conducted in these countries were contacted for further information. Each of the papers obtained was indexed and thoroughly reviewed to extract all relevant information. The following information was obtained: study period for the data presented (the year the study started and ended), duration of the study, number of children less than five years included, overall number of deaths during the study, number of deaths due to malaria, person-years of follow-up, all-cause mortality, and malaria-specific mortality. The information in the papers was cross-checked twice to ensure that the information extracted was consistent with the information in the original paper.

The literature review identified thirty nine longitudinal (clinical, epidemiological, cohort) studies from The Gambia in which malaria had been studied among children below five years of age. Twenty-one of the 39 studies had information on mortality (seventeen of these studies contained cause-specific mortality information). In addition, ten surveys and censuses were identified for which only all-cause mortality information was available.

Similarly, eighteen longitudinal studies on malaria where identified for Burkina Faso, with eight studies containing mortality information. Three of these studies contained cause-specific mortality information. In addition, fifteen surveys and censuses were identified for which all-cause mortality information was available.

In six studies (four from The Gambia, two from Burkina Faso) 212223242526, a separate rate estimation for the control arm was performed.

This study has reviewed, summarized and compared all-cause and malaria-specific mortality rates for The Gambia and Burkina Faso. Many studies have been conducted in The Gambia to investigate different aspects of malaria (1960–2000) in contrast to Burkina Faso where only a few studies have been conducted since the late 1980s to early 2000s. Findings based on censuses, surveys and longitudinal studies show that child mortality in the Gambia has declined significantly. Reasons for this decline are likely to include socio-economic development, improved health services including the establishment of primary health care and immunisation programmes and specific intervention projects 25293435. However, since 1990, this decline in mortality has slowed down. In parts of Africa where HIV/AIDS is a major problem, mother-to-child transmission has been a major explanation for this rebound in child mortality 36. However, The Gambia and Burkina Faso have not been severely affected by the African HIV/AIDS epidemic and seroprevalence rates in adults remain less than 4% in both countries 37.

Estimates of mortality rates from nationally representative surveys conducted from 1960 to 2003 show that child mortality has also declined in Burkina Faso. However, this trend is not clearly discernable in the few studies for which mortality was estimated from DSS longitudinal studies because of coverage of only a few years. Nevertheless, results from DSS studies from the two countries during the period 1992 to 1999 yield very comparable estimates for under-five mortality rates, although results from surveys and censuses for under-five mortality rates are slightly different for the later years. This observation suggests the need for caution in generalising results from DSS longitudinal studies to represent national figures. Differences in observed mortality rates from nationally representative surveys could be a reflection of differences in national health policies and programmes in the two countries whereas the comparable rates obtained from the DSS based studies could be due to the effects of interventions (such as insecticide treated bednets, vaccination programmes, primary health care service delivery etc) that are routinely implemented among the DSS populations 3839.

It is not easy to fully interpret the data provided in Figures 1, 2 and 3. However, overall, all-cause mortality rates fell in both countries during the study period covered, although some peaks occurred in the early 1990's in The Gambia. Malaria mortality rates did not show a similar decline. This could be partly due to parasite resistance to chloroquine, the first-line drug for treatment of malaria during those years, as well as to a break down in community based health services due to some under-funding by the national government during the years that followed 1990 40414243. There is some evidence that in The Gambia the incidence of clinical malaria is now beginning to decline (Cessay, personal communication).

Mortality differences across age groups are evident in the two countries. The observed differences in age-mortality patterns are reminiscent of mortality in other countries in SSA where the mortality rates for children in the age-group 1 and 4 have been noted to be lower than the infant mortality rate 44. In this review, the ratio of infant mortality rate to child mortality rate has been shown to have increased over time. The overall risk of dying in the first year has declined over time, but not to the same extent as the decline in the risk of dying between the ages of one and four years. Possible explanations for these results include introduction of the expanded immunization programmes (EPI) which might have had a bigger effect on CMR than on U5MR. For instance, measles is no longer a major cause of death in children between one and four years of age in many parts of Africa where effective EPI programmes are well established 45. Other explanations might include improvements in nutrition with deaths due to malnutrition in older children being averted 46.

The estimated malaria mortality rates of 9.5 (The Gambia) and 15.4 (Burkina Faso) per 1,000 person-years differ considerably but are within the previous estimates for SSA 47. Numerous interventions have been undertaken in The Gambia that may have had an effect on malaria including the introduction of village-based health services and insecticide-treated bednets (ITNs) 344348. Previous studies have shown variable evidence for the link between malaria mortality rates and malaria transmission intensities 4950. In Burkina Faso, the annual average entomological inoculation rate (EIR) is above 80 while in The Gambia an annual average EIR is less than 50 infectious bites per person per year 16. Therefore, differences in estimated malaria mortality rates might be a reflection of differences in malaria transmission patterns, although this is controversial 1151.

This study has several limitations. It is possible that other relevant literature might have been left out, especially literature that was not published online or in the English language. However, it is likely that the mortality trends observed are not significantly biased due to this limitation. The fact that different studies were designed to answer a given research question makes comparison of studies difficult. The sampling methods and aims of the surveys were different and although cross-comparison of child mortality rates between studies is possible, such comparisons needs to be treated with caution. On the other hand, population censuses should provide a complete enumeration and mortality rates estimated from the census should be more realistic without major sampling errors. For instance, mortality rates resulting from a bednet intervention study cannot easily be compared to mortality rates resulting from a study that evaluated the performance of primary health care. The latter is most likely to give rates that are lower due to the direct protection provided by the mosquito net which lowers malaria transmission rates. Furthermore, the gross differences in the years covered by the malaria-related studies conducted in the two countries made comparisons of estimates difficult. In The Gambia, studies have been conducted over a longer period than in Burkina Faso where most studies were conducted after the year 1990.

Efforts were made to standardize rates by either computing person years or presenting results in the same units for the same age-group categories. For some studies it was difficult to achieve such standardized rates especially when computing malaria-specific mortality rates. In many papers, desired details were not available and it was not possible to make estimates for all age-specific mortality rates.

Despite all these limitations, this review demonstrates that with available data, mortality patterns can be compared across countries in Africa. However, caution is needed in extrapolating the results obtained in DSS surveys to give national rates. Further work will include investigating the linkage between malaria transmission parameters and child mortality. This needs to be done locally using DSS based data since estimates cannot be readily inferred from national mortality figures.

The author(s) declare that they have no competing interests.

RPN coordinated the study, performed the statistical analysis and drafted the manuscript.

HB designed, supervised and participated in coordination of the study and writing-up of the manuscript.

HR supervised the analysis and coordination of the study and participated in writing-up of the manuscript.

MJ substantially participated in the conception in particular with regard to the studies in The Gambia and writing-up of the manuscript.

AS substantially participated in the conception in particular with regard to the studies in Burkina Faso and writing-up of the manuscript.

BK substantially participated in the conception in particular with regard to the studies in Burkina Faso and writing-up of the manuscript.

BG substantially participated in the conception in particular with regard to the studies from The Gambia, in the interpretation of the results, formulating the discussion and writing-up of the manuscript.

OM substantially participated in the conception, analysis and interpretation of the results, formulating the discussion and writing-up of the manuscript.