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A recent national survey in Tanzania reported that mortality in children younger than 5 years dropped by 24% over the 5 years between 2000 and 2004. We aimed to investigate yearly changes to identify what might have contributed to this reduction and to investigate the prospects for meeting the Millennium Development Goal for child survival (MDG 4). We analysed data from the four demographic and health surveys done in Tanzania since 1990 to generate estimates of mortality in children younger than 5 years for every 1-year period before each survey back to 1990. We estimated trends in mortality between 1990 and 2004 by fitting Lowess regression, and forecasted trends in mortality in 2005 to 2015. We aimed to investigate contextual factors, whether part of Tanzania's health system or not, that could have affected child mortality.

Disaggregated estimates of mortality showed a sharp acceleration in the reduction m mortality in children younger than 5 years in Tanzania between 2000 and 2004. In 1990, the point estimate of mortality was 141.5 (95% CI 141.5-141.5) deaths per 1000 livebirths. This was reduced by 40%, to reach a point estimate of 83.2 (95% CI 70.1-96.3) deaths per 1000 livebirths in 2004. The change in absolute risk was 58.4 (95% CI 32.7-83.8; p<0.0001). Between 1999 and 2004 we noted important improvements in Tanzania's health system, including doubled public expenditure on health; decentralisation and sector-wide basket funding; and increased coverage of key child-survival interventions, such as integrated management of childhood illness, insecticide-treated nets, vitamin A supplementation, immunisation, and exclusive breastfeeding.

Other determinants of child survival that are not related to the health system did not change between 1999 and 2004, except for a slow increase in the HIV/AIDS burden. Tanzania could attain MDG 4 if this trend of improved child survival were to be sustained. Investment in health systems and scaling up interventions can produce rapid gains in child survival.

Discussion

In Tanzania, the most recent demographic and health survey in 2005 showed a 24% improvement in child survival, with mortality rates in children younger than 5 years down from 147 deaths per 1000 for 1994-99 to 112 deaths per 1000 for 2000-04 (p<0.02).15,33 In national birth-history surveys, these 5-year averages conceal the pattern and degree of change in yearly rates. Since this 5-year change substantially exceeded 15%, the minimum regarded by Korenromp and colleagues14 as indicative of a true reduction, we decided to calculate the yearly rates to examine the pattern of the reduction and to see if the point estimate for the year 2004 differed from historical values or from period average.

Our analysis of the annual rates shows a pattern of continuous reduction in mortality reaching 83 . 2 (95% CI 70.1-96.3) deaths per 1000 in 2004. Within the 2004-05 survey data, five of the six lowest values over the 15 years were recorded in the last 5 years," indicating that mortality in this group fell by 40% between 1990 and 2004. Based on Tanzania's 2002 population of 34.4 million, this finding suggests that 280000 children's lives were saved between 1999 and 2005 that would otherwise have been lost had the prevailing rate of the 1990s continued.

Our analyses of data from all four demographic and health surveys, analysed by year of reference, thus suggest that Tanzania is on the trajectory necessary to achieve MDG 4by 2015, for a range of different weightings of past performance in the distant or near past, back to 1990. Our results differ from those of an analysis of all available data from direct and indirect estimates of mortality disaggregated into 2-year intervals, including data before 1990, which concluded that Tanzania would not be able to achieve this goal.6 However, the data from before 1990 can have little bearing on the ability to achieve a goal for which the starting point is 1990, especially since the purpose of the MDG was to elicit changes in trends. To assume that the trend before 1990 continued would imply that setting the goal was futile. In this specific instance, performance was poor before 1990, and inclusion of earlier data biases the conclusion towards a slower improvement. Furthermore, all extrapolations must, of necessity, assume a degree of continuity in the underlying processes, and so tend to over-smooth if a trend accelerates, as it seems to have done in Tanzania in about 2000. Since aggregation of the data into longer time-units tends to increase the degree of this smoothing, we disaggregated the data into shorter time units.

The large reduction in mortality evident since 2000 immediately raises questions about the quality of surveys and data and about comparability over time. Additional quality control was provided for the 2004-05 demographic and health survey and its data precisely because fewer child deatiis were recorded than were expected." Under-reporting bias could also have occurred, for example if maternal mortality increased because of HIV/AIDS or other factors. The cross- sectional demographic and health surveys did not gather information about children whose mothers died. However, the demographic surveillance systems in Tanzania, which track entire populations longitudinally, also reported reductions in mortality in children younger than 5 years, which substantiates the data from the demographic and health surveys." Furthermore, demographic and health surveys in 1999 and 2005 did not detect any major increases in maternal mortality between these two periods, although such changes would be difficult to detect in sample sizes used in the demographic and health surveys. With respect to deaths of mothers due to HIV/AIDS, reduced mortality in children younger than 5 years is probably not an artifact caused by the under-reported deaths, since the estimated magnitude of this effect in a rural Tanzanian population with an HIV prevalence of 4.3% would underestimate deaths in children younger than 5 years by only 2.3%.36

If we assume that our finding of a reduction in mortality for children younger than 5 years is real, what can explain this apparent acceleration of survival in Tanzania after a decade of high but static mortality rates in the 1990s? And can this improvement be sustained? We examined differences in the health system in Tanzania between 1999 and 2004 and in external factors that could reasonably be expected to have contributed to large survival gains over this short period. Between 1999 and 2004, Tanzania more than doubled its public expenditure on health; such increased expenditure has been strongly correlated with increased survival in children younger than 5 years in developing countries, especially in poor people.37 Increased public expenditure on health could also be especially powerful in decentralised health systems when such resources are targeted towards essential cost-effective interventions.38 Tanzania implemented such governance shifts towards greater decentralisation in 2000, by introducing sector-wide capitation grants that gave districts substantial financial resources. This was perhaps one of the most important distinctions in Tanzania's health system between the 1990s and the 2000s, since it opened opportunities for local problem solving and provided resources for districts to selectively increase resources for key interventions, as has been shown in pilot studies since 1996.38

Decentralisation allowed the introduction and scale-up of new interventions such as the integrated management of childhood illness, which facilitated adoption of new treatment policies for malaria that replaced failing first-line treatments with more effective case management for the largest single cause of death for children. The IMCI programme also assisted promotion of the use of insecticide-treated nets for malaria prevention. Sentinel districts had piloted the introduction of IMCI from 1997, with full provision, increased use, and effective coverage by 1999-2000.39 Impact studies showed that, after a 2-year follow-up, IMCI was associated with 13% lower child mortality in pilot districts that had health-system strengthening man in other districts.40 Other pilot studies in Tanzania showed the high local effectiveness of insecticide-treated nets for reduction of mortality in children of this age.41

Tanzania started nationwide scale-up of insecticide-treated nets in 1999 and of IMCI in 2000, and changed its drug policy for malaria in 2001. Since malaria mortality in Tanzania is concentrated in postneonatal infants younger than 5 years,42 the survival gains recorded in the 2004-05 demographic and health survey were highest for postneonatal infants, suggesting that malaria-specific mortality reduction has made progress. Moreover, several sentinel sites in Tanzania, which monitor cause-specific mortality by use of continuous longitudinal demographic surveillance systems, also reported reductions in mortality in children younger than 5 years before the findings of the 2004-05 demographic and health surveys, and detected declines in malaria and acute febrile illness deaths in children younger than 5 years.34,43 These findings add plausibility to the hypothesis that the collective effect of a multifaceted approach to malaria contributed to child-survival gains during this period.44 Coverage of other child-survival interventions, such as vitamin A supplementation,45 exclusive breastfeeding, oral rehydration therapy and iron supplementation for children, increased. For other interventions, such as antenatal care an immunisation, coverage was already high, and did not change.

Modelling showed that a 33% reduction of mortality in children younger than 5 years could be expected between 1999 and 2004, from 129 to 86 deaths per 1000 livebirths. These effects would mainly be in reduction of postneonatal mortality in children younger than 5 years. The predicted failure to affect neonatal (and maternal) mortality draws attention to problems with the continuum of care necessary to achieve MDGs. The general scarcity of data and analyses continues to limit programme efforts and monitoring of progress.

Among factors not related to the health system, gams in wealth would be expected to exert a major effect on survival in children younger than 5 years. Tanzania has enjoyed many decades of political stability and, in recent years, steady economic growth. Nevertheless, GDP per person has increased by only 93 international dollars (US$47) over the 5 years between 1999 and 2004. An increase of this size corresponds to an expected decrease in mortality in children younger than 5 years of 2 . 2%, on the basis of a regression of GDP (in international dollars) per person and mortality in children younger than 5 years for 45 sub-Saharan countries (data reanalysed from WHO statistics).27 Although important, this growth in national wealth would be unlikely to account for much of our finding of a 40% reduction in mortality, especially since the proportion of the population living below the absolute poverty line and food poverty line in the 1990s had improved only slightly in 2002. Although gains have been made in the education of Tanzania's current cohort of schoolchildren, child-health outcomes are affected by the educational status of parents, which had improved only marginally by 2004. Early child-bearing and short birth-spacing both raise the risk of child mortality, and the total fertility rate, average age at first birth, adolescent childbearing, and median birth intervals remained similar in the two periods. Hence changes in fertility probably did not contribute to our findings of a large improvement in child survival.

We did not find evidence of any major epidemics (for example, of measles or meningitis) that might have occurred in the late 1990s but not in the early 2000s. Conversely, adult and child mortality due to HIV/AIDS continued to increase slowly,43 and therefore differentials in HIV/AIDS interventions might have affected overall mortality, since 25% of children who are born to HIV-positive mothers are infected. The PMTCT programme is a proven cost-effective combination of strategies and interventions that can be tailored to specific local conditions. These interventions and strategies, including voluntary and confidential counselling and testing, provision of antiretroviral drugs to HIV-positive pregnant women, planning of safe delivery procedures, and counselling about appropriate infant-feeding options, can reduce mother-to-child transmission by 50%. However, in Tanzania access to HIV/AIDS interventions such as voluntary counselling and testing, PMTCT, and antiretrovirals was not yet sufficient as of 2004 to have affected child survival on a national scale. Epidemic patterns, including HIV/AIDS and its response, can therefore be excluded as an explanation for the reduction in child mortality, and could even have worked against this trend.

Nutrition can be determined by health systems (eg, micronutrient supplementation and other health sector interventions) and by other factors (eg, food insecurity, poverty, climate shocks, and natural disasters). We did not identify evidence of major events outside the health system that could have contributed to changes in nutritional status in Tanzania during the study period. However, the nutritional status of children did improve slightly, possibly because of better access to various general health interventions (eg, IMCI, insecticide-treated nets, and vitamin A supplementation), and slight gains in wealth. Improved nutritional status is likely to have contributed to the reduced risk of mortality in children younger than 5 years.

If we assume that the trend is real, and is due to a strengthening health system and increased access to key child-survival interventions, can this trend be continued? It should be noted that the most recent demographic and health survey, in 2004-05, preceded the potential effect of increased funding to Tanzania from the Global Fund to Fight HIV/AIDS, Tuberculosis and Malaria. Although the first grants were announced in late 2002, the actual programmes that they supported did not begin until late 2004, and the benefits would not have been detectable in the last demographic and health survey but can be expected to assist the downward trend into the future. For children, these funds will boost access to insecticide-treated nets through a national voucher scheme, which is designed to provide the nets to all pregnant women and their newborn babies, which started in late 2004. Scaling up the PMTCT programme and antiretroviral therapy started in 2005; programmes for zinc supplementation and oral rehydration therapy started in 2007; and access to improved antimalarial treatment through artemisinin combination therapy in 2007.

Since neonatal mortality remains constant and forms an increasing share of the mortality in children younger than 5 years, it could emerge as a barrier to continued reductions in mortality and attainment of MDG 4. Renewed efforts are being planned to address neonatal and maternal mortality in Tanzania. These efforts will coincide with a doubling in the sector-wide district basket fund for the Tanzanian health system to US$1.00 per person per year. Such continued efforts at scaling up will need concomitant investments in strengthening of health systems, including management of human resources, procurement and supply chain management, health information management, and constant attention to enhancing quality of care.

We were unable to estimate the relative contributions of different factors in the health system to reduction of child mortality since 2000. However, the collective weight of so many positive changes in the health system, in the absence of other explanations, is compelling. Rather, we could ask why we would not expect to see gains in survival.5 Broad, multifaceted progress in stewardship, public expenditure on health, decentralised financing, resource allocation, and better coverage of essential child-survival services can work synergistically to effect important progress towards MDG 4 in low-income countries such as Tanzania. Increased health resources combined with strengthening of decentralised health systems to ensure that life-saving interventions reach those in need is a key child-survival strategy.