Measuring Transitions in Sexual Risk Among Men Who Have Sex With Men: The Novel Use of Latent Class and Latent Transition Analysis in HIV Sentinel Surveillance

New combination human acquired deficiency (HIV) prevention strategies that include biomedical and primary prevention approaches add complexity to the task of measuring sexual risk. Latent transition models are beneficial for understanding complex phenomena; therefore, we trialed the application of latent class and latent transition models to HIV surveillance data. Our aims were to identify sexual risk states and model individuals' transitions between states. A total of 4,685 HIV-negative men who have sex with men (MSM) completed behavioral questionnaires alongside tests for HIV and sexually transmissible infections at one of 2 Melbourne, Victoria, Australia, general practices (2007-2013). We found 4 distinct classes of sexual risk, which we labeled "monogamous" (n = 1,224), "risk minimizer" (n = 1,443), "risk potential" (n = 1,335), and "risk taker" (n = 683). A positive syphilis, gonorrhea, or chlamydia test was significantly associated with class membership. Among a subset of 516 MSM who had at least 3 clinic visits, there was general stability across risk classes; MSM had on average a 0.70 (i.e., 70%) probability of remaining in the same class between visits 1 and 2 and between visits 2 and 3. Monogamous MSM were one exception; the probability of remaining in the monogamous class was 0.51 between visits 1 and 2. Latent transition analyses identified unobserved risk patterns in surveillance data, characterized high-risk MSM, and quantified transitions over time.

Recalibration of the limiting antigen avidity EIA to determine mean duration of recent infection in divergent HIV-1 subtypes

Background

Mean duration of recent infection (MDRI) and misclassification of long-term HIV-1 infections, as proportion false recent (PFR), are critical parameters for laboratory-based assays for estimating HIV-1 incidence. Recent review of the data by us and others indicated that MDRI of LAg-Avidity EIA estimated previously required recalibration. We present here results of recalibration efforts using >250 seroconversion panels and multiple statistical methods to ensure accuracy and consensus.

Methods

A total of 2737 longitudinal specimens collected from 259 seroconverting individuals infected with diverse HIV-1 subtypes were tested with the LAg-Avidity EIA as previously described. Data were analyzed for determination of MDRI at ODn cutoffs of 1.0 to 2.0 using 7 statistical approaches and sub-analyzed by HIV-1 subtypes. In addition, 3740 specimens from individuals with infection >1 year, including 488 from patients with AIDS, were tested for PFR at varying cutoffs.

Results

Using different statistical methods, MDRI values ranged from 88–94 days at cutoff ODn = 1.0 to 177–183 days at ODn = 2.0. The MDRI values were similar by different methods suggesting coherence of different approaches. Testing for misclassification among long-term infections indicated that overall PFRs were 0.6% to 2.5% at increasing cutoffs of 1.0 to 2.0, respectively. Balancing the need for a longer MDRI and smaller PFR (<2.0%) suggests that a cutoff ODn = 1.5, corresponding to an MDRI of 130 days should be used for cross-sectional application. The MDRI varied among subtypes from 109 days (subtype A&D) to 152 days (subtype C).

Conclusions

Based on the new data and revised analysis, we recommend an ODn cutoff = 1.5 to classify recent and long-term infections, corresponding to an MDRI of 130 days (118–142). Determination of revised parameters for estimation of HIV-1 incidence should facilitate application of the LAg-Avidity EIA for worldwide use.

Increases in newly acquired HIV infections in Victoria, Australia: epidemiological evidence of successful prevention?

BACKGROUND

Rates of newly acquired HIV notifications provide useful data for monitoring transmission trends.

METHODS

We describe 10-year (2001-10) trends in newly acquired HIV notifications in Victoria, Australia. We also examine recent trends in HIV testing and incidence and risk behaviours among gay and other men who have sex with men (MSM) attending four high MSM caseload clinics.

RESULTS

Between 2001 and 2010 there was a significant increasing linear trend in newly acquired HIV that was driven primarily by increases between 2009-2010. MSM accounted for 85% of newly acquired HIV notifications. Between 2007-10, the total number of HIV tests per year at the high caseload clinics increased 41% among MSM and HIV incidence declined by 52%; reported risk behaviours remained relatively stable among these MSM.

CONCLUSION

More newly acquired HIV notifications may reflect recent increased testing among MSM; continued scrutiny of surveillance data will assess the sustained effectiveness of testing as prevention, health promotion and the contribution of risk and testing behaviours to HIV surveillance outcomes.

The impact of HIV treatment as prevention in the presence of other prevention strategies: lessons learned from a review of mathematical models set in resource-rich countries

OBJECTIVE

We aimed to assess the potential prevention benefits of HIV treatment as prevention (TasP) in resource-rich countries and examine the potential interactions between TasP and other prevention strategies by reviewing mathematical models of TasP.

METHOD

Multiple databases were searched for mathematical models published in the previous 5 years (from July 2007 to July 2012). The nine models located were set in Canada, Australia and the United States.

RESULTS

These models' predictions suggested that the impact of expanding treatment rates on expected new infections could range widely, from no decrease to a decrease of 76%, depending on the time horizon, assumptions and the form of TasP modeled. Increased testing, reducing sexually transmitted infections and reducing risky practices were also predicted to be important strategies for decreasing expected new infections. Sensitivity analysis suggests that current uncertainties such as the effectiveness of highly active antiretroviral therapy outside of heterosexual transmission, less than ideal adherence, and risk compensation, could impact on the success of TasP at the population level.

CONCLUSION

The results from large scale pilots and community randomized controlled trials will be useful in demonstrating how well this prevention approach works in real world settings, and in identifying the factors that are needed to support its effectiveness.

Guidance and practice on frequency of HIV and sexually transmitted infection testing in men who have sex with men - what is the European situation?

Men who have sex with men (MSM) are at particular risk for HIV/sexually transmitted infections (STI). To investigate the European guidance used for MSM STI and HIV screening, risk level profiling and how this translated to practice, we conducted a questionnaire survey of leading physicians in the European branch of the International Union against Sexually Transmitted Infections (IUSTI). We identified that most European countries have limited guidance on screening intervals for MSM. Where risk profiling is advised, it is often left to clinicians to weight different behaviours and decide on screening frequency. Our results suggest that European MSM STI and HIV testing guidelines be developed with clear and specific recommendations around screening intervals and risk profiling. These guidelines will be particularly helpful due to rapidly evolving models of sexual healthcare, and the emergence of new providers who may benefit from guidelines that require less interpretation.

Stop the drama Downunder: a social marketing campaign increases HIV/sexually transmitted infection knowledge and testing in Australian gay men

INTRODUCTION

Since 2000, notifications of HIV and other sexually transmitted infections (STIs) have increased significantly in Australian gay men. We evaluated the impact of a social marketing campaign in 2008-2009 aimed to increase health-seeking behavior and STI testing and enhance HIV/STI knowledge in gay men.

METHODS

A convenience sample of 295 gay men (18-66 years of age) was surveyed to evaluate the effectiveness of the campaign. Participants were asked about campaign awareness, HIV/STI knowledge, health-seeking behavior, and HIV/STI testing. We examined associations between recent STI testing and campaign awareness. Trends in HIV/STI monthly tests at 3 clinics with a high case load of gay men were also assessed. Logistic and Poisson regressions and χ tests were used.

RESULTS

Both unaided (43%) and aided (86%) campaign awareness was high. In a multivariable logistic regression, awareness of the campaign (aided) was independently associated with having had any STI test within the past 6 months (prevalence ratio = 1.5; 95% confidence interval = 1.0-2.4. Compared with the 13 months before the campaign, clinic data showed significant increasing testing rates for HIV, syphilis, and chlamydia among HIV-negative gay men during the initial and continued campaign periods.

CONCLUSION

These findings suggest that the campaign was successful in achieving its aims of increasing health-seeking behavior, STI testing, and HIV/STI knowledge among gay men in Victoria.

Vaccination to protect against infection of the female reproductive tract

Infection of the female genital tract can result in serious morbidities and mortalities from reproductive disability, pelvic inflammatory disease and cancer, to impacts on the fetus, such as infant blindness. While therapeutic agents are available, frequent testing and treatment is required to prevent the occurrence of the severe disease sequelae. Hence, sexually transmitted infections remain a major public health burden with ongoing social and economic barriers to prevention and treatment. Unfortunately, while there are two success stories in the development of vaccines to protect against HPV infection of the female reproductive tract, many serious infectious agents impacting on the female reproductive tract still have no vaccines available. Vaccination to prevent infection of the female reproductive tract is an inherently difficult target, with many impacting factors, such as appropriate vaccination strategies/mechanisms to induce a suitable protective response locally in the genital tract, variation in the local immune responses due to the hormonal cycle, selection of vaccine antigen(s) that confers effective protection against multiple variants of a single pathogen (e.g., the different serovars of Chlamydia trachomatis) and timing of the vaccine administration prior to infection exposure. Despite these difficulties, there are numerous ongoing efforts to develop effective vaccines against these infectious agents and it is likely that this important human health field will see further major developments in the next 5 years.

Disproportionate impact of combination antiretroviral therapy on AIDS incidence in Australia: results from a modified back-projection model

The objective of the current study is to describe the impact of Combination antiretroviral therapy (cART) on trends in AIDS incidence over time for selected population groups in Australia, specifically, men who have sex with men (MSM) and injecting drug users (IDUs). A modified back-projection modeling technique was used to predict the number of AIDS diagnoses without cART based on Australia's HIV/AIDS surveillance system database. Modelled estimates indicate that since 1996, the effective cART has reduced overall AIDS cases by ~70 and ~10% among MSM and IDUs respectively. The predicted reduction in AIDS cases among IDUs aged less than 40 years was 36% while there was no reduction predicted for those aged 40 years or older. The impact of cART on AIDS diagnoses has been modest among IDUs. Late presentation, poor access to health services and barriers to uptake of cART may account for the divergence between these population groups.

Increasing HIV diagnoses in Australia among men who have sex with men correlated with the growing number not taking antiretroviral therapy

BACKGROUND

Australia has experienced rising notifications of HIV diagnoses despite widely available combination antiretroviral therapy (CART). New HIV diagnoses have also been younger than the average age of those living with HIV. We investigated the degree to which several risk factors could explain this rise in notifications and the younger age profile.

METHODS

Numbers and ages of men who have sex with men (MSM) living with HIV in Australia from 1983 to 2007 were calculated from notifications of HIV diagnoses and deaths. We compared the trend over time as well as the average ages of MSM newly diagnosed with HIV infection from 1998 to 2007 with those for: notifications of gonorrhoea and syphilis, total MSM living with HIV infection, and the component not on CART.

RESULTS

The percentage of younger MSM not taking CART has increased since 1998 (aged <30 years P<0.001; 30-39 years P=0.004). The trend of new HIV diagnoses was most significantly correlated with the total number of MSM living with HIV infection and the sector not taking CART (P<0.0001). Based on similarity of average ages, MSM living with HIV infection and not taking CART was the best predictor of the increasing trend in new HIV diagnoses (99.9999% probability, Akaike information criterion).

CONCLUSIONS

Our analyses suggest MSM living with HIV infection and not taking CART could be the source of the increase in HIV infections. Consequently, greater CART enrolment should decrease HIV incidence, especially in younger MSM.

Mathematical models for the study of HIV spread and control amongst men who have sex with men

For a quarter of century, mathematical models have been used to study the spread and control of HIV amongst men who have sex with men (MSM). We searched MEDLINE and EMBASE databases up to the end of 2010 and reviewed this literature to summarise the methodologies used, key model developments, and the recommended strategies for HIV control amongst MSM. Of 742 studies identified, 127 studies met the inclusion criteria. Most studies employed deterministic modelling methods (80%). Over time we saw an increase in model complexity regarding antiretroviral therapy (ART), and a corresponding decrease in complexity regarding sexual behaviours. Formal estimation of model parameters was carried out in only a small proportion of the studies (22%) while model validation was considered by an even smaller proportion (17%), somewhat reducing confidence in the findings from the studies. Nonetheless, a number of common conclusions emerged, including (1) identification of the importance of assumptions regarding changes in infectivity and sexual contact rates on the impact of ART on HIV incidence, that subsequently led to empirical studies to gather these data, and (2) recommendation that multiple strategies would be required for effective HIV control amongst MSM. The role of mathematical models in studying epidemics is clear, and the lack of formal inference and validation highlights the need for further developments in this area. Improved methodologies for parameter estimation and systematic sensitivity analysis will help generate predictions that more fully express uncertainty, allowing better informed decision making in public health.

Characteristics of HIV epidemics driven by men who have sex with men and people who inject drugs

PURPOSE OF REVIEW

To highlight the latest developments in mathematical transmission modelling of HIV epidemics among men who have sex with men (MSM) and people who inject drugs (PWID).

RECENT FINDINGS

Mathematical approaches have been applied to a wide range of topics in recent HIV research. Epidemiological models have evaluated past and forecasted future trends in prevalence and incidence, evaluated innovative behaviour modification strategies and public health programmes aimed at minimizing risk, and explored the potential impact of various biomedical interventions. MSM have developed new risk reduction strategies which models have deemed to be effective at a population level only in certain settings, such as when there are high rates of HIV testing. Modelling has also indicated that persistent circulation of drug-resistant HIV strains is likely to become an inevitable public health issue in the near future in resource-rich settings among MSM. Models have also recently been used to demonstrate that needle and syringe programmes for harm reduction among PWID are effective and cost-effective.

SUMMARY

Mathematical modelling is particularly amenable to single population groups of concentrated HIV epidemics, such as among MSM and PWID. Models have been utilized to evaluate innovative areas in clinical, biomedical and public health research that cannot be conducted in other population groups. Future directions are likely to include evaluation of specific public health programmes and providing understanding of the importance of specific treatment regimens and incidence and interaction of comorbid conditions associated with HIV.

Trends in detectable viral load by calendar year in the Australian HIV observational database

Background

Recent papers have suggested that expanded combination antiretroviral treatment (cART) through lower viral load may be a strategy to reduce HIV transmission at a population level. We assessed calendar trends in detectable viral load in patients recruited to the Australian HIV Observational Database who were receiving cART.

Methods

Patients were included in analyses if they had started cART (defined as three or more antiretrovirals) and had at least one viral load assessment after 1 January 1997. We analyzed detectable viral load (>400 copies/ml) in the first and second six months of each calendar year while receiving cART. Repeated measures logistic regression methods were used to account for within and between patient variability. Rates of detectable viral load were predicted allowing for patients lost to follow up.

Results

Analyses were based on 2439 patients and 31,339 viral load assessments between 1 January 1997 and 31 March 2009. Observed detectable viral load in patients receiving cART declined to 5.3% in the first half of 2009. Predicted detectable viral load based on multivariate models, allowing for patient loss to follow up, also declined over time, but at higher levels, to 13.8% in 2009.

Conclusions

Predicted detectable viral load in Australian HIV Observational Database patients receiving cART declined over calendar time, albeit at higher levels than observed. However, over this period, HIV diagnoses and estimated HIV incidence increased in Australia.

Increasing HIV transmission through male homosexual and heterosexual contact in Australia: results from an extended back-projection approach

OBJECTIVES

The aim of the study was to reconstruct the HIV epidemic in Australia for selected populations categorized by exposure route; namely, transmission among men who have sex with men (MSM), transmission among injecting drug users (IDUs), and transmission among heterosexual men and women in Australia.

DESIGN

Statistical back-projection techniques were extended to reconstruct the historical HIV infection curve using surveillance data. Methods We developed and used a novel modified back-projection modelling technique that makes maximal use of all available surveillance data sources in Australia, namely, (1) newly diagnosed HIV infections, (2) newly acquired HIV infections and (3) AIDS diagnoses.

RESULTS

The analyses suggest a peak HIV incidence in Australian MSM of approximately 2000 new infections per year in the late 1980s, followed by a rapid decline to a low of <500 in the early 1990s. We estimate that, by 2007, cumulatively approximately 20 000 MSM were infected with HIV, of whom 13% were not diagnosed with HIV infection. Similarly, a total of approximately 1050 and approximately 2600 individuals were infected through sharing needles and heterosexual contact, respectively, and in 12% and 23% of these individuals, respectively, the infection remained undetected.

DISCUSSION

Male homosexual contact accounts for the majority of new HIV infections in Australia. However, the transmission route distribution of new HIV infections has changed over time. The number of HIV infections is increasing substantially among MSM, increasing moderately in those infected via heterosexual exposure, and decreasing in IDUs.

Development of two avidity-based assays to detect recent HIV type 1 seroconversion using a multisubtype gp41 recombinant protein

Current laboratory methods to detect recent HIV-1 infection for the estimation of incidence have various limitations, including varying performance in different subtypes or populations. Therefore, new methods are needed to detect recent infections with increased specificity. We developed a recombinant protein, rIDR-M, that covered divergent sequences from the immunodominant region (IDR) of gp41 from all major subtypes and recombinants of HIV-1 group M and expressed in Escherichia coli. The rIDR-M protein was highly reactive with HIV antibodies in sera from different subtypes and equivalently detected antibodies to divergent subtypes B and AE from Thailand, in contrast to individual gp41 peptides derived from respective subtypes, suggesting that it can be used for incidence assays. The protein was used in two different assay formats to measure antibody avidity: (1) a two-well avidity index assay (AI-EIA) and (2) a new one-well limiting antigen avidity assay (LAg-avidity EIA), both with a pH 3.0 buffer to dissociate low-avidity antibodies present during early infection. Limiting the amount of antigen allowed detection of recent HIV-1 infection, with or without dissociation buffer, but the detection was most efficient when the pH 3.0 dissociation buffer was included. When a well-characterized 41-member seroincidence panel (20 recent and 21 long-term) was used, both the two-well AI-EIA and one-well LAg-avidity EIA efficiently distinguished recent and long-term infections. The new avidity-based assays using rIDR-M antigen may improve the accuracy of detecting recent HIV-1 infection and allow a better estimation of incidence in diverse HIV-1 subtypes.

Importance of promoting HIV testing for preventing secondary transmissions: modelling the Australian HIV epidemic among men who have sex with men

BACKGROUND

We address the research questions: (i) what proportion of new HIV infections is transmitted from people who are (a) undiagnosed, (b) in primary HIV infection (PHI), (c) on antiretroviral therapy?; and (ii) what is the expected epidemiological impact of (a) increasing the proportion of newly acquired HIV infections receiving early treatment, and (b) increasing HIV testing rates?

METHODS

We used a mathematical model to simulate HIV transmission in the population of men who have sex with men (MSM) in Australia. We calibrated the model using established biological and clinical data and a wide range of Australian MSM epidemiological and behavioural data sources.

RESULTS

We estimate that ~19% of all new HIV infections are transmitted from the ~3% of Australian HIV-infected MSM who are in PHI; ~31% of new HIV infections are estimated to be transmitted from the ~9% of MSM with undiagnosed HIV. We estimate that the average number of infections caused per HIV-infected MSM through the duration of PHI is ~0.14-0.28.

CONCLUSIONS

The epidemiological impact of increasing treatment in PHI would be modest due to insufficient detection of newly-infected individuals. In contrast, increases in HIV testing rates could have substantial epidemiological consequences. The benefit of testing will also increase over time. Promoting increases in the coverage and frequency of testing for HIV could be a highly-effective public health intervention, but the population-level impact of interventions based on promoting early treatment of patients diagnosed in PHI is likely to be small. Treating PHI requires further evaluation of its long-term effects on HIV-infected individuals.

Rapidly ageing HIV epidemic among men who have sex with men in Australia

BACKGROUND

Antiretroviral therapy has increased survival for individuals living with HIV and has led to an ageing of this population in developed countries. To date the rate of ageing has been unquantified, giving rise to uncertainty in the treatment emphasis and burden in this population.

METHODS

A mathematical model was used in conjunction with HIV/AIDS data from the Australian National HIV/AIDS Registry to estimate numbers and ages of Australian men who have sex with men (MSM) living with HIV infection from 1980 to 2005.

RESULTS

The average age of HIV-infected Australian MSM is estimated to exceed 44 years of age by the year 2010 and has increased by 1 year of age for each two calendar years since the mid-1980s. HIV-infected MSM over 60 years of age have been increasing in number by 12% per year since 1995. A consequence of successful therapy with subsequent ageing of those infected has meant that from 2001 estimated deaths from other causes exceed AIDS deaths in Australia.

CONCLUSIONS

In summary, our analyses indicate an increasing and rapidly ageing population living with HIV in Australia. This will inevitably lead to more serious non-AIDS conditions in ageing patients living with HIV, and to increased treatment complexity.