Trends in three decades of HIV/AIDS epidemic in Thailand by nonparametric backcalculation method. AIDS

Trends in three decades of HIV/AIDS epidemic in Thailand by nonparametric backcalculation method. AIDS

To reconstruct the past HIV incidence and prevalence in Thailand from 1980 to 2008 and predict the country’s AIDS incidence from 2009 to 2011, nonparametric backcalculation was adopted utilizing 100 quarterly observed new AIDS counts excluding paediatric cases. The accuracy of data was enhanced through a series of data adjustments using the weight method to account for several surveillance reporting issues. The mixture of time-dependent distributions allowed the effects of age at seroconversion and antiretroviral therapy to be incorporated simultaneously. Sensitivity analyses were conducted to assess model variations that were subject to major uncertainties. Future AIDS incidence was projected for various predetermined HIV incidence patterns. HIV incidence in Thailand reached its peak in 1992 with approximately 115 000 cases. A steep decline thereafter discontinued in 1997 and was followed by another strike of 42 000 cases in 1999. The second surge, which happened concurrently with the major economic crisis, brought on 60 000 new infections. As of December 2008, more than 1 million individuals had been infected and around 430 000 adults were living with HIV corresponding to a prevalence rate of 1.2%. The incidence rate had become less than 0.1% since 2002. The backcalculated estimates were dominated by postulated median AIDS progression time and adjustments to surveillance data. The authors’ analysis indicated that, thus far, the 1990s was the most severe era of HIV epidemic in Thailand with two HIV incidence peaks. A drop in new infections led to a decrease in recent AIDS incidence, and this tendency is likely to remain unchanged until 2011, if not further.

Editors’ note: Backcalculation reconstructs a past pattern of HIV incidence based on AIDS surveillance data and a plausible incubation period from HIV infection to AIDS diagnosis. The relatively short incubation period of 7 years used in this work may have lowered the estimates of backcalculated total infections. Although it makes logical sense that the large cuts of one-third to one-half in government HIV prevention budgets during the financial crisis of 1998 to 2000 could have led to an intriguing second peak in HIV incidence in Thailand, further study is needed to confirm this.