HIV This Week

Stover J, Johnson P, Zaba B, Zwahlen M, Dabis F and Ekpini RE. The Spectrum projection package: improvements in estimating mortality, ART needs, PMTCT impact and uncertainty bounds. Sex. Transm. Inf. 2008;84;i24-i30

The approach to national and global estimates of HIV used by UNAIDS starts with estimates of adult HIV prevalence prepared from surveillance data using either the Estimation and Projection Package (EPP) or the Workbook. Time trends of prevalence are transferred to Spectrum to estimate the consequences of the HIV epidemic, including the number of people living with HIV, new infections, AIDS deaths, AIDS orphans, treatment needs and the impact of treatment on survival. The UNAIDS Reference Group on Estimates, Modelling and Projections regularly reviews new data and information needs and recommends updates to the methodology and assumptions used in Spectrum. The latest update to Spectrum was used in the 2007 round of global estimates. Several new features have been added to Spectrum in the past two years. The structure of the population was reorganised to track populations by HIV status and treatment status. Mortality estimates were improved by the adoption of new approaches to estimating non-AIDS mortality by single age, and the use of new information on survival with HIV in non-treated cohorts and on the survival of patients on antiretroviral treatment. A more detailed treatment of mother-to-child transmission of HIV now provides more prophylaxis and infant feeding options. New procedures were implemented to estimate the uncertainty around each of the key outputs. The latest update to the Spectrum programme is intended to incorporate the latest research findings and provide new outputs needed by national and international planners.

Editors’ note: This article provides excellent background on the inner workings and assumptions of the Spectrum projection package, that continues to evolve as new evidence comes forward and new procedures are introduced. These include new information on mortality from long-running cohorts and the effects of antiretroviral treatment on survival, as well as adjustments to better estimate uncertainty around the estimates. These refinements are increasing our understanding of the scope and magnitude of the HIV epidemic and are helping plan more effective responses at both national and international levels.

Human immunodeficiency virus type 1 (HIV-1) CRF08_BC and CRF07_BC are two major recombinants descended from subtypes B' and C. Despite their massive epidemic impact in China, their migration patterns and divergence times remain unknown. Phylogenetic and population genetic analyses were performed on 228 HIV-1 sequences, representing CRF08_BC, CRF07_BC and subtype C strains from different locations across China, India and Myanmar. Genome-specific rates of evolution and divergence times were estimated using a Bayesian MCMC framework under various evolutionary models. CRF08_BC originated in 1990.3 (95% credible region, CR: 1988.6-1991.9) in Yunnan province, before spreading to Guangxi (south) and Liaoning (northeast) around 1995. Inside Guangxi region, the eastward expansion of CRF08_BC continued from Baise city (west) to Binyang (central) between 1997 and 1998, and later spread into Pingxiang around 1999 in the south, mainly through injecting drug use. Additionally, CRF07_BC diverged from its common ancestor in 1993.3 (95% CR: 1991.2-1995.2) before crossing the border into southern Taiwan in late 1990s. Phylogenetic analysis indicates that both CRF08_BC and CRF07_BC can trace their origin to Yunnan. The parental Indian subtype C lineage likely entered China around 1981.2 (95% CR: 1976.7-1985.9). Using multiple unlinked loci model, we also showed that the dates of divergence calculated in this study may not be significantly affected by intrasubtype recombination among different lineages. This is the first phylodynamic study depicting the spatiotemporal dynamics of HIV/AIDS in East Asia.

Editors’ note: Yunnan, located in south-western China, borders on the ‘Golden Triangle’ of south-east Asia, one of the world’s largest heroin producing regions. It is considered to be an epicentre of HIV in China - the first case was detected there in 1989. Recombination, an intrinsic evolutionary mechanism that shapes HIV diversity, creates a footprint that permits tracking of HIV transmission over time and through space. Genealogical analysis of these footprints reconstructs the epidemiological history of viral populations, enhancing understanding of HIV transmission to improve prevention programming .

Bangladesh has been conducting annual serological surveillance for HIV and syphilis since 1998 among most at-risk populations including sex workers, males having sex with males, injecting drug users (IDUs) and heroin smokers. During the seventh round conducted between January and June 2006, 10,368 people were sampled and the overall HIV prevalence was 0.9%. The highest HIV rate was recorded in male IDUs from the capital city Dhaka (7%), and the rates have risen significantly over the rounds (P < 0.001). In Dhaka, most of the HIV-positive IDUs (10.5%) were localized in one neighbourhood, while in the remaining neighbourhoods 1% were positive (P < 0.001). In all other groups, HIV prevalence was <1%. Active syphilis rates were highest in female IDUs (9.9%) followed by female street-based sex workers (8.6%). However, rates in female sex workers in Dhaka declined significantly over the years (P < 0.001). Bangladesh has to act urgently to prevent escalation of the epidemic.

Editors’ note: Bangladesh ’s move from a low prevalence to a concentrated epidemic has been slow but predictable, given documented ongoing risk among populations at highest risk of HIV exposure, particularly injecting drug users (IDU). Localisation of the concentrated IDU epidemic in one neighbourhood gives hope that a focused effort to provide more intensive comprehensive and effective harm reduction services to this neighbourhood, with diffusion outward to IDU throughout the country, could help turn the epidemic in this population around.