Empirical validation of the UNAIDS Spectrum model for subnational HIV estimates: case-study of children and adults in Manicaland, Zimbabwe

Abstract

Background: More cost-effective HIV control may be achieved by targeting geographical areas with high infection rates. The AIDS Impact model of Spectrum - used routinely to produce national HIV estimates - could provide the required subnational estimates but is rarely validated with empirical data, even at a national level.

Design: The validity of the Spectrum model estimates were compared with empirical estimates.

Methods: Antenatal surveillance and population survey data from a population HIV cohort study in Manicaland, East Zimbabwe, were input into Spectrum 5.441 to create a simulation representative of the cohort population. Model and empirical estimates were compared for key demographic and epidemiological outcomes. Alternative scenarios for data availability were examined and sensitivity analyses were conducted for model assumptions considered important for subnational estimates.

Results: Spectrum estimates generally agreed with observed data but HIV incidence estimates were higher than empirical estimates, whereas estimates of early age all-cause adult mortality were lower. Child HIV prevalence estimates matched well with the survey prevalence among children. Estimated paternal orphanhood was lower than empirical estimates. Including observations from earlier in the epidemic did not improve the HIV incidence model fit. Migration had little effect on observed discrepancies - possibly because the model ignores differences in HIV prevalence between migrants and residents.

Conclusion: The Spectrum model, using subnational surveillance and population data, provided reasonable subnational estimates although some discrepancies were noted. Differences in HIV prevalence between migrants and residents may need to be captured in the model if applied to subnational epidemics.

Fig. 1.. Fitting the Spectrum model to data on the local HIV epidemic in Manicaland, east Zimbabwe: The effects of including data from general population surveys.

ANC, ante-natal clinics. HIV prevalence among male (a) and female (b) adults. HIV incidence among male (c) and female (d) adults.

Fig. 2.. Comparison of model (main scenario) and empirical estimates for all-cause mortality in all adults and HIV⁺ adults.

Death rate among all 15–49 males (dark dots), and females (grey triangles) as predicted by Spectrum (a). Death rate among 15+ HIV⁺ males (dark dots), and females (grey triangles) as predicted by Spectrum (b). Overall mortality rates by age among males (c-g), and females (h-k). Error bars and shaded areas represent 95%CI of data.

Fig. 3.. Comparison of model (main scenario) and empirical estimates for the child outcomes.

(a) HIV age-prevalence among children in 2010 by model version (current and older). Shaded area shows the 95%CI range for the empirical estimates. (b) Orphan by form of orphanhood over time. Spectrum estimates (lines) compared with the 95% confidence intervals of household survey data estimates (polygons) and Demographic and Health Survey data for Manicaland province, Zimbabwe (squares, dots and triangles).

Fig. 4.. Comparison of model (with and without migration) and empirical estimates for population age structure in 2010.

Male (a) and female (b) population age structure in 2010. HIV incidence among male (c) and female (d) adults when migration is included (solid lines) or not (dashed lines).

Fig. 5.. The effect on HIV prevalence and incidence estimates of including data from earlier in the epidemic in Spectrum model fits. ANC, ante-natal clinics.

HIV prevalence among male (a) and female (b) adults. HIV incidence among male (c) and female (d) adults.