Back-calculation and projection of the HIV/AIDS epidemic among homosexual/ bisexual men in three European countries: evalution of past projections and updates allowing for treatment effects

A Method to Estimate the Size and Characteristics of HIV-positive Populations Using an Individual-based Stochastic Simulation Model

It is important not only to collect epidemiologic data on HIV but to also fully utilize such information to understand the epidemic over time and to help inform and monitor the impact of policies and interventions. We describe and apply a novel method to estimate the size and characteristics of HIV-positive populations. The method was applied to data on men who have sex with men living in the UK and to a pseudo dataset to assess performance for different data availability. The individual-based simulation model was calibrated using an approximate Bayesian computation-based approach. In 2013, 48,310 (90% plausibility range: 39,900-45,560) men who have sex with men were estimated to be living with HIV in the UK, of whom 10,400 (6,160-17,350) were undiagnosed. There were an estimated 3,210 (1,730-5,350) infections per year on average between 2010 and 2013. Sixty-two percent of the total HIV-positive population are thought to have viral load <500 copies/ml. In the pseudo-epidemic example, HIV estimates have narrower plausibility ranges and are closer to the true number, the greater the data availability to calibrate the model. We demonstrate that our method can be applied to settings with less data, however plausibility ranges for estimates will be wider to reflect greater uncertainty of the data used to fit the model.

Is back-projection methodology still relevant for estimating HIV incidence from national surveillance data?

Accurate estimates of HIV incidence are crucial to understand the extent of transmission of the infection, evaluate intervention strategies and effectively plan new public health control measures. HIV/AIDS surveillance systems in numerous industrialised countries record the number of known new HIV and/or AIDS diagnoses, which are often used as a surrogate marker for HIV incidence. HIV/AIDS diagnosis data have been used to reconstruct historical HIV incidence trends using modified back-projection methods. Estimates of HIV incidence are most robust when reliable data on the number of incident infections, a subset of all diagnoses, is widely available, and surveillance systems should prioritise the collection of these data. Back-projection alone provides reliable estimates of HIV incidence in the past, but is not useful when estimating current or future HIV incidence. However, back-projection methodology should be used in conjunction with other corroborative methods to estimate current HIV incidence, and methods to combine the various techniques should be investigated.

The cost-effectiveness of HIV voluntary counseling and testing in China

China has experienced a dramatic increase in the number of HIV infections. To control the AIDS epidemic, free HIV voluntary counseling and testing has been made available in China. This study compared the cost-effectiveness of this program for 2 populations-the general population and men who have sex with men (MSM), to examine the value for money of this program. A Bernoulli-process model has been used to translate the changes in sexual behaviors to the number of HIV infections averted. Costs are estimated from a societal perspective. The outcomes are measured in terms of the incremental cost per HIV infection averted and the incremental cost per disability-adjusted life-year averted. The study found that the voluntary counseling and testing for the general population is not cost-effective based on the threshold adopted, whereas the same HIV prevention program for MSM is cost-saving. These results suggest that the efficiency of resources used could be substantially improved by appropriately targeting high-risk population groups. Therefore measures should be taken to increase the uptake of this intervention among high-risk groups.

Correcting the actual reproduction number: a simple method to estimate R(0) from early epidemic growth data

The basic reproduction number, R₀, a summary measure of the transmission potential of an infectious disease, is estimated from early epidemic growth rate, but a likelihood-based method for the estimation has yet to be developed. The present study corrects the concept of the actual reproduction number, offering a simple framework for estimating R₀ without assuming exponential growth of cases. The proposed method is applied to the HIV epidemic in European countries, yielding R₀ values ranging from 3.60 to 3.74, consistent with those based on the Euler-Lotka equation. The method also permits calculating the expected value of R₀ using a spreadsheet.

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

OBJECTIVES

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.

METHODS

Nonparametric backcalculation was adopted utilizing 100 quarterly observed new AIDS counts excluding pediatric 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.

RESULTS

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.

CONCLUSION

Our analysis indicated that, thus far, the 1990s was the most severe era of HIV/AIDS 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.

"Get back to where you once belonged": monitoring the AIDS pandemic in the 21st century

This paper reviews the concepts and methodological strategies that have shaped the monitoring of the AIDS pandemic, today in its third decade. A deliberate effort was made to highlight aspects usually forgotten by the canon. The paper aims to track the footsteps of the evolving strategies in the field of surveillance & monitoring, with the help of disciplines such as epidemiology, molecular biology, social, and behavioral sciences. The deep divide that opposes societies severely affected by the epidemic and affluent societies much less affected by the epidemic is contrasted with the scarce human and financial resources of the societies facing harshest epidemic vis-à-vis the comprehensiveness of the response to the epidemic in their affluent counterparts in terms of the scope and high standards of their initiatives on monitoring, prevention, management & care. The pressing need to implement feasible alternatives to the current sophisticated and expensive ones is briefly discussed. Beyond the renewed challenge posed to the creativity of scientists and health professionals, the AIDS pandemic is described as a major public health crisis, compromising the social fabric in some contexts, and as a never fulfilled calling for an ethics of solidarity between different societies and different social strata of each given society.

[Aspects of rehabilitation in HIV and AIDS]

Medical treatment of HIV infection has changed dramatically since 1997. The uncontrollable threat became a chronic disease. On the other hand, many HIV-infected people suffer from high psychological distress and multiple physical complaints. Interaction in HIV prevention could transform into psychological counseling. Counselors should initiate rehabilitation measures and occupational reintegration by utilizing all legal possibilities for handicapped people. Patients and physicians, psychologists and social workers as well as self-help groups should initiate successful reintegration into the workforce and daily life; this could positively influence compliance behavior.