Incorporating scale dependence in disease burden estimates: the case of human African trypanosomiasis in Uganda

Abstract

Background: The WHO has established the disability-adjusted life year (DALY) as a metric for measuring the burden of human disease and injury globally. However, most DALY estimates have been calculated as national totals. We mapped spatial variation in the burden of human African trypanosomiasis (HAT) in Uganda for the years 2000-2009. This represents the first geographically delimited estimation of HAT disease burden at the sub-country scale.

Methodology/principal findings: Disability-adjusted life-year (DALY) totals for HAT were estimated based on modelled age and mortality distributions, mapped using Geographic Information Systems (GIS) software, and summarised by parish and district. While the national total burden of HAT is low relative to other conditions, high-impact districts in Uganda had DALY rates comparable to the national burden rates for major infectious diseases. The calculated average national DALY rate for 2000-2009 was 486.3 DALYs/100 000 persons/year, whereas three districts afflicted by rhodesiense HAT in southeastern Uganda had burden rates above 5000 DALYs/100 000 persons/year, comparable to national GBD 2004 average burden rates for malaria and HIV/AIDS.

Conclusions/significance: These results provide updated and improved estimates of HAT burden across Uganda, taking into account sensitivity to under-reporting. Our results highlight the critical importance of spatial scale in disease burden analyses. National aggregations of disease burden have resulted in an implied bias against highly focal diseases for which geographically targeted interventions may be feasible and cost-effective. This has significant implications for the use of DALY estimates to prioritize disease interventions and inform cost-benefit analyses.

Figure 1. Study area.

Shaded districts in Uganda affected by HAT over the study period, 2000–2009.

Figure 2. Total HAT burden in Uganda by parish, 2000–2009.

Shaded parishes indicate the total burden in DALYs estimated over the ten-year study period, as modelled with an under-reporting rate of 40% .

Figure 3. Temporal variation in HAT burden by parish, 2000–2009.

Total DALYs per year, as modelled with an under-reporting rate of 40%, are shown as averaged over the 2000–2009 historical period, and four sub-periods. DALYs/year were calculated and mapped by parish, and district boundaries are shown.

Figure 4. Comparison of average annual DALY rates for HAT and other infectious diseases.

The calculated historic average annual DALY rates by district population over the period 2000–2009 are shown in grey. The calculated national average DALY rate for HAT and 2004 GBD DALY rates for HAT and major infectious diseases in Uganda are shown in black. Estimates of completeness of case reporting for HAT (33% gambiense, 5% rhodesiense) and DALY rates for other diseases are taken from the GBD 2004 report .