Back-calculation by birth cohort, incorporating age- specific disease progression, pre-AIDS mortality and change in European AIDS case definition. European Union Concerted Action on Multinational AIDS Scenarios

Rates and Correlates of HIV Incidence in Namibia's Zambezi Region From 2014 to 2016: Sentinel, Community-Based Cohort Study

BACKGROUND

Direct measures of HIV incidence are needed to assess the population-level impact of prevention programs but are scarcely available in the subnational epidemic hotspots of sub-Saharan Africa. We created a sentinel HIV incidence cohort within a community-based program that provided home-based HIV testing to all residents of Namibia's Zambezi region, where approximately 24% of the adult population was estimated to be living with HIV.

OBJECTIVE

The aim of this study was to estimate HIV incidence, detect correlates of HIV acquisition, and assess the feasibility of the sentinel, community-based approach to HIV incidence surveillance in a subnational epidemic hotspot.

METHODS

Following the program's initial home-based testing (December 2014-July 2015), we purposefully selected 10 clusters of 60 to 70 households each and invited residents who were HIV negative and aged ≥15 years to participate in the cohort. Consenting participants completed behavioral interviews and a second HIV test approximately 1 year later (March-September 2016). We used Poisson models to calculate HIV incidence rates between baseline and follow-up and multivariable Cox proportional hazard models to assess the correlates of seroconversion.

RESULTS

Among 1742 HIV-negative participants, 1624 (93.23%) completed follow-up. We observed 26 seroconversions in 1954 person-years (PY) of follow-up, equating to an overall incidence rate of 1.33 per 100 PY (95% CI 0.91-1.95). Among women, the incidence was 1.55 per 100 PY (95% CI 1.12-2.17) and significantly higher among those aged 15 to 24 years and residing in rural areas (adjusted hazard ratio [aHR] 4.26, 95% CI 1.39-13.13; P=.01), residing in the Ngweze suburb of Katima Mulilo city (aHR 2.34, 95% CI 1.25-4.40; P=.01), who had no prior HIV testing in the year before cohort enrollment (aHR 3.38, 95% CI 1.04-10.95; P=.05), and who had engaged in transactional sex (aHR 17.64, 95% CI 2.88-108.14; P=.02). Among men, HIV incidence was 1.05 per 100 PY (95% CI 0.54-2.31) and significantly higher among those aged 40 to 44 years (aHR 13.04, 95% CI 5.98-28.41; P<.001) and had sought HIV testing outside the study between baseline and follow-up (aHR 8.28, 95% CI 1.39-49.38; P=.02). No seroconversions occurred among persons with HIV-positive partners on antiretroviral treatment.

CONCLUSIONS

Nearly three decades into Namibia's generalized HIV epidemic, these are the first estimates of HIV incidence for its highest prevalence region. By creating a sentinel incidence cohort from the infrastructure of an existing community-based testing program, we were able to characterize current transmission patterns, corroborate known risk factors for HIV acquisition, and provide insight into the efficacy of prevention interventions in a subnational epidemic hotspot. This study demonstrates an efficient and scalable framework for longitudinal HIV incidence surveillance that can be implemented in diverse sentinel sites and populations.

Estimation of the burden of people living with Human Immunodeficiency Virus/Acquired Immunodeficiency Syndrome (HIV/AIDS) in Kerala state, India

Background

Worldwide, 36.7 million people were infected with Acquired Immunodeficiency Syndrome (AIDS) by the end of 2015. Over the period 2007 to 2015, there was a declining trend in the prevalence of adult Human Immunodeficiency Virus (HIV) in the state of Kerala, India. The current study aims to find a suitable statistical modelling technique for the distribution of HIV incubation time and predict the cumulative number of AIDS cases.

Materials and Methods

The requisite data were obtained from the Kerala State AIDS Control Society (KSACS) for the years 2007 to 2015. To assess the distribution of HIV incubation time, the data of 22 HIV-infected Keralite patients were retrieved from the medical records of a teaching hospital. Data included age, gender, and incubation time. The back-calculation method was utilized to predict the cumulative HIV/AIDS cases.

Results

The estimated total cumulative AIDS cases in Kerala for the years 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014 and 2015 were found to be 35,777, 48,944, 62,039, 45,669, 45,668, and 43,605, 42,377, 39,362, 37,617, 39,583, 25,414 respectively using back-calculation method with Weibull (2) incubation time distribution. The mean incubation time of the total HIV cases (male and female) was 4.4 years which indicates a rapid progression of the disease in the state of Kerala.

Conclusion

The back-calculation method is a powerful tool to estimate the cumulative frequency of AIDS cases; which predicted a declining HIV trend among Keralites. Moreover, the Weibull distribution is the best fitted distribution for HIV incubation time in our population.

Bayesian evidence synthesis for a transmission dynamic model for HIV among men who have sex with men

Understanding infectious disease dynamics and the effect on prevalence and incidence is crucial for public health policies. Disease incidence and prevalence are typically not observed directly and increasingly are estimated through the synthesis of indirect information from multiple data sources. We demonstrate how an evidence synthesis approach to the estimation of human immunodeficiency virus (HIV) prevalence in England and Wales can be extended to infer the underlying HIV incidence. Diverse time series of data can be used to obtain yearly “snapshots” (with associated uncertainty) of the proportion of the population in 4 compartments: not at risk, susceptible, HIV positive but undiagnosed, and diagnosed HIV positive. A multistate model for the infection and diagnosis processes is then formulated by expressing the changes in these proportions by a system of differential equations. By parameterizing incidence in terms of prevalence and contact rates, HIV transmission is further modeled. Use of additional data or prior information on demographics, risk behavior change and contact parameters allows simultaneous estimation of the transition rates, compartment prevalences, contact rates, and transmission probabilities.

New challenges for mathematical and statistical modeling of HIV and hepatitis C virus in injecting drug users

Injecting drug users are not only driving blood-borne transmission of HIV and hepatitis C virus but also likely drive sexual transmission of HIV in large parts of the world. Mathematical and statistical modeling can provide important insights in these epidemiological processes and on the potential impact of interventions but have been little used to date. This review aims to discuss the potential areas of application of modeling in the field of viral infections in injecting drug users. After reviewing key examples of published modeling work on HIV and hepatitis C virus in injecting drug users, we discuss recent developments in the epidemiology, diagnosis, treatment and prevention of these infections. In particular, new methods for the diagnosis of early HIV infection, new antivirals for a more effective treatment of HIV, hepatitis B and hepatitis C virus infections, new concepts in design and surveillance of interventions for drug users and increasing possibilities of molecular typing of pathogens are changing the questions and decisions for public health policy makers who deal with drug-related infectious diseases. Research including mathematical modeling is needed to understand the impact of new diagnostic tools, new treatment options and combined intervention strategies on the epidemiology of viral infections in injecting drug users. Methodological advances in mathematical modeling are required to adequately approach some of the ensuing research questions. Modeling has much to offer for solving urgent policy questions, but current levels of funding in modeling research are insufficient and need to be scaled up to make better use of these possibilities.

Estimation and prediction of the HIV–AIDS-epidemic under conditions of HAART using mixtures of incubation time distributions

The estimation of the HIV-AIDS epidemic by means of back-calculation (BC) has been difficult since the introduction of highly active anti-retroviral therapy (HAART) because the incubation time distributions needed for BC were poorly known. Moreover, it has been assumed that if the general public is aware that effective treatments are available then the majority of infected people would be known, and therefore a hidden epidemic was assumed not to exist. Nevertheless, it was suspected that not every infected person would come to the attention of health-care providers, and therefore estimates independent of the patients' registration were necessary. In this paper, the incubation time distributions for HIV treated with the HAART regimen are derived from a cohort study. By using estimates of the proportion treated according to the HAART regimen and the incubation time distributions estimated in the era before the implementation of HAART (pre-HAART), new marginal population incubation time distributions for each of the three risk groups (homosexuals, drug users and others) were constructed. The BC was performed using an empirical Bayesian approach based on the latter incubation time distribution.

The changing face of the HIV epidemic in western Europe: what are the implications for public health policies?

In this review, we describe changes in dynamics of HIV transmission and shifts in affected populations in western Europe using HIV/AIDS surveillance data and published and unpublished reports. Despite substantial reductions in HIV-related morbidity and mortality since the introduction of highly active antiretroviral treatment, HIV continues to pose a major public health problem in western Europe. More than half a million people are living with an infection that remains incurable and requires costly lifelong treatment; many people remain unaware of their infection, and thousands of new infections continue to occur every year. Migrants from countries with a high prevalence of HIV/AIDS, notably sub-Saharan Africa, bear a disproportionate and increasing share of HIV throughout western Europe and, in most countries, account for the majority of heterosexually acquired HIV infections diagnosed in recent years. Prevention, treatment, and care must be adapted to reach migrant populations. Following a resurgence of risky sexual behaviour, HIV transmission may now be increasing among homosexual and bisexual men, and renewed safer sex campaigns are urgently needed.

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

This study critically evaluates the quality of 1990 back-calculations and long-term projections of the HIV/AIDS epidemic for homosexual/bisexual men in France, the Federal Republic of Germany, and the UK. The projection captured the general pattern observed in all three countries although the observed AIDS incidence peaked 2-3 years later and declined faster than had been projected. Total AIDS incidences from 1989 to 2000 were overestimated by 38.5% in France, and underestimated by 23.9 and 17.5% in western Germany and the UK. Updated back-calculations and projections to 2020 use AIDS incidence data up to 2000. The procedure incorporates an asymmetric long-tailed cumulative HIV curve as well as the increase in the median incubation period brought about by new therapies introduced during the 1990s. The results suggest that: (i) The rapid decrease in cases during the late 1990s was caused by a median incubation period that increased from 10 years to 21-23 years by the late 1990s. (ii) An imminent bottoming out followed by a protracted increase in AIDS cases from 2000 to at least 2010 could be the consequence of a leveling off of the median incubation period. (iii) A low variant of the projections shows that at least 40,000 homosexual men could develop AIDS in the three countries after 2000.

Estimating the cumulative number of human immunodeficiency virus diagnoses by cross-linking from four different sources

BACKGROUND

We estimated the cumulative number of people diagnosed with human immunodeficiency virus (HIV) infection in a region of Italy by cross-linking data from four surveillance systems and applying capture-recapture methods.

METHODS

The study was conducted using data referring to residents of the Veneto Region (population 4.4 million). We cross-linked data from the AIDS Registry (data 1983-2000), the HIV Registry (1988-2000), the Death Registry (1992-1999), and the Hospital-Discharge Registry (1997-2000), using a code based on name, birth date, and sex. A specific software for capture-recapture models (CARE-1) was used to estimate the size of the target population with two different statistical approaches (sample coverage and log-linear models).

RESULTS

A total of 2801 people were reported to the AIDS Registry, 6415 to the HIV Registry, 1598 to the Death Registry as HIV/AIDS-related deaths, and 3330 to the Hospital-Discharge Registry with a diagnosis of HIV infection. Overall, 8723 people were present in at least one registry: 4896 people were present in only one registry, 2387 in two registries, 1286 in three registries, and 154 in all four registries. Using the sample coverage approach, we estimated that, since the beginning of the epidemic in Veneto, an estimated 11 281 people (95% CI: 10 981, 11 621) should have been reported to at least one registry; thus the estimated coverage of the four registries was 77.3% (i.e. 8723/11 281). Results obtained applying the log-linear approach were similar, although the fitting of this model was not adequate.

CONCLUSIONS

Cross-linking data from four different sources and applying the capture-recapture method can improve the accuracy of the estimates of the dimensions of the HIV epidemic.

Current situation and regional perspective on HIV/AIDS surveillance in europe

AIDS reporting has been the principal means of monitoring the HIV/AIDS situation in Europe since 1984 [corrected]. HIV reporting was set up at the European level in 1999, although it has existed in most European countries since the 1980s. Anonymous individual data on AIDS and, if available, new HIV diagnoses, and data on HIV prevalence in various populations are reported from the 51 countries of the WHO European Region to EuroHIV, and aggregate data on HIV prevalence in various populations [corrected]. Data are presented after grouping the 51 countries into three geographic areas: the West, Center, and East. At end of 2000, in the West, AIDS incidence continued to decline except among those infected heterosexually; numbers of newly diagnosed HIV infections are relatively stable, but rising among heterosexually infected persons, many of whom originate from countries with generalized HIV epidemics. In the East, numbers of newly diagnosed HIV cases (mostly injection drug users) continue to rise steeply, particularly in the Russian Federation, Latvia, and Estonia. In the Center, levels of HIV and AIDS remain low. HIV reporting is becoming a central element of HIV/AIDS surveillance in Europe. Heterogeneity between countries in health care systems, HIV testing patterns and surveillance systems remain challenging for data standardization at the European level. Efforts should be made to use surveillance data for evaluating the effectiveness of HIV/AIDS prevention interventions.