Estimating HIV incidence and detection rates from surveillance data

BACKGROUND: Markov models that incorporate HIV test information can increase precision in estimates of new infections and permit the estimation of detection rates. The purpose of this study was to assess the functioning of a Markov model for estimating new HIV infections and HIV detection rates in Louisiana using surveillance data. METHODS: We expanded a discrete-time Markov model by accounting for the change in AIDS case definition made by the Centers for Disease Control and Prevention in 1993. The model was applied to quarterly HIV/AIDS surveillance data reported in Louisiana from 1981 to 1996 for various exposure and demographic subgroups. When modeling subgroups defined by exposure categories, we adjusted for the high proportion of missing exposure information among recent cases. We ascertained sensitivity to changes in various model assumptions. RESULTS: The model was able to produce results consistent with other sources of information in the state. Estimates of new infections indicated a transition of the HIV epidemic in Louisiana from (1) predominantly white men and men who have sex with men to (2) women, blacks, and high-risk heterosexuals. The model estimated that 61% of all HIV/AIDS cases were detected and reported by 1996, yet half of all HIV/non-AIDS cases were yet to be detected. Sensitivity analyses demonstrated that the model was robust to several uncertainties. CONCLUSIONS: In general, the methodology provided a useful and flexible alternative for estimating infection and detection trends using data from a U.S. surveillance program. Its use for estimating current infection will need further exploration to address assumptions related to newer treatments.     

Date of first positive HIV test: reliability of information collected for HIV/AIDS surveillance in the United States

OBJECTIVES: This study examined the reliability of the first positive HIV test date reported in the U.S. HIV/AIDS Reporting System (HARS). This date is essential to determine case counts for resource allocation for HIV treatment and prevention efforts. METHODS: The dates of first positive HIV tests reported by individuals with HIV in an interview survey conducted in 16 states (n=16,394, interviewed 1995-2002) were compared with the dates of HIV diagnosis reported to HARS. The percentage of agreement for the year of diagnosis and the weighed kappa (k) with 95% confidence intervals (CIs) was calculated. RESULTS: Self-reported year of diagnosis agreed with the year of diagnosis in HARS for 56% of date pairs (k=0.69; 95% CI 0.68, 0.70); 30% reported an earlier diagnosis year. Agreement differed by sex, age, race, exposure, and reason or place of testing (p<.01). Lower agreement was found when the self-reported diagnostic test was anonymous (k=0.57; 95% CI 0.52, 0.62) compared with confidential tests (k=0.66; 95% CI 0.64, 0.68). Lower agreement was also found for cases first reported with AIDS (k=0.58; 95% CI 0.55, 0.62) compared with cases first reported with HIV not AIDS (k=0.71; 95% CI 0.70, 0.73) as well as for participants interviewed three years or more after their HARS diagnosis date (k=0.55; 95% CI 0.52, 0.57) compared with those interviewed within one year (k=0.62; 95% CI 0.61, 0.63). More than 20% of participants in almost all groups, however, reported earlier diagnosis years than those recorded in HARS. CONCLUSION: As many as 30% of HIV diagnoses may have occurred earlier than recorded in HARS. Additional studies need to determine mechanisms to adequately capture diagnosis dates in HARS.     

Estimating HIV prevalence and projecting AIDS incidence in the United States: a model that accounts for therapy and changes in the surveillance definition of AIDS.

The AIDS incubation distribution is changing in calendar time because of treatment and changes in the surveillance definition of AIDS. To obtain reliable estimates of HIV prevalence and projections of AIDS incidence in the 1990s using the method of backcalculation, we constructed an appropriate incubation distribution for each calendar date of infection. We parameterized the impact of treatment on the incubation distribution by specifying the relative hazard for AIDS in treated versus untreated people as a function of duration of HIV infection. To account for trends in the incubation distribution, we modelled the prevalence of treatment, the distribution of treatment onset times, and the impact of the revision of the AIDS surveillance definition in 1987. We selected and evaluated backcalculation models based on consistency with external information. We defined a 'plausible range' of estimates that took into account uncertainty about the natural incubation distribution and treatment efficacy, as well as bootstrap assessment of stochastic error. Using these methods, we projected that national United States AIDS incidence will plateau during 1991-1994 at over 50,000 cases per year. Projections exhibited substantial systematic uncertainty, and we calculated a plausible range for AIDS incidence in 1994 of 42,300 to 70,700 cases. An estimated 628,000 to 988,000 cumulative HIV infections occurred as of 1 January 1991. After accounting for AIDS mortality, we estimated that 484,000 to 844,000 people were living with HIV infection on 1 January 1991. Favourable trends in HIV incidence appeared in gay men and intravenous drug users. Plausible ranges for our estimates overlapped with those from a 'stage model' approach to incorporating treatment effects in backcalculations. Our approach, however, tended to yield smaller estimates of epidemic size, mainly because the parameters used with the stage model implied that more treatment was in use and that treatment was more effective than in our model.     

Trends in HIV and AIDS based on HIV/AIDS surveillance data in Japan

BACKGROUND: In recent years a decline in the number of new AIDS cases has been observed in several industrialized countries. It is important to know whether these recent trends observed in North America and Europe are also occurring in Japan. METHODS: The number of people reported with HIV and AIDS by nationality, route of infection, and sex was calculated based on the HIV/AIDS surveillance data available in Japan through December 1997. The effect of reporting delay, which was defined as those HIV and AIDS cases reported in the calendar year following diagnosis, on the trends was examined. The coverage rate in reporting HIV cases was estimated as the ratio of the reported AIDS cases with prior report as an HIV-positive to the total number of reported AIDS cases. RESULTS: The cumulative number of reported cases of HIV among Japanese and non-Japanese residents of Japan up to the end of 1997 were 1,300 and 1,190, respectively. The cumulative number of reported cases of AIDS among Japanese and non-Japanese up to the end of 1997 were 758 and 298, respectively. The number of reported cases of HIV among Japanese was found to be still increasing, with the major contribution from male cases. The increasing trend in the number of reported AIDS cases among Japanese began to slow in 1996 and 1997. The number of reported cases of HIV among non-Japanese residents of Japan peaked in 1992, and has decreased since then, and remained constant after 1994. In contrast, the number of reported AIDS cases among these non-Japanese tended to increase gradually. There was a slight reporting delay for people with HIV and AIDS. The estimated coverage rate in reporting HIV cases tended to decrease in 1996 and 1997 (1/7.2, 1/10.2, respectively). We point out several reasons for this recent decline and suggest the possibility of an ostensible decline in the estimates. CONCLUSIONS: We suggest that the number of people with HIV among Japanese has continued to increase, and that the increase in the number of AIDS cases among Japanese is now slowing.     

HIV/AIDS Among African-Born Residents in the United States

The number of African-born residents living in the United States (US) increased by more than 750 % between 1980 and 2009. HIV diagnosis rates in this population are six times higher than estimated incidence in the general US population. African-immigrants with HIV are also diagnosed at later stages of infection than US-born residents, but they paradoxically have lower mortality after diagnosis. There are higher rates of HIV among women, higher rates of heterosexual transmission, and lower rates of injection-drug-use-associated transmission among African-born residents in the US relative to the general US population. Despite this distinct epidemiologic profile, surveillance reports often group African-born residents with US-born Blacks. The high rates of HIV among African-born residents in the US combined with increasing immigration and incomplete surveillance data highlight the need for more accurate epidemiologic data along with appropriate HIV service programs.     

Subpopulation estimates from the HIV incidence surveillance system--United States, 2006

CDC has created an HIV incidence surveillance system in selected areas of the United States as a component of its national human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS) reporting system. The purpose of the new system is to estimate the number of new HIV infections occurring each year in the United States. Initial results published recently for 2006 showed that 73% of new infections were in males, 45% were in blacks, and 53% were in men who have sex with men (MSM). To provide additional subpopulation estimates by age group, race/ethnicity, and HIV transmission category, CDC conducted a more detailed analysis of data from the new surveillance system. The results indicated that, in 2006, of new HIV infections among males, 72% were in MSM. Among MSM with new infections, 46% were white, 35% were black, and 19% were Hispanic. Among MSM aged 13-29 years, the number of new HIV infections in blacks (5,220) was 1.6 times the number in whites (3,330) and 2.3 times the number in Hispanics (2,300). Among females, the predominant HIV transmission category was high-risk heterosexual contact, which accounted for 80% of new infections. The HIV incidence rate for black females was 14.7 times the rate for white females, and the rate for Hispanic females was 3.8 times the rate for white females. MSM (of all races), blacks, and Hispanics were represented disproportionately in 2006 among those with new HIV infections. The new incidence data will help guide local, state, and national intervention measures tailored to those populations at greatest risk for HIV infection.     

Estimating HIV incidence using dates of both HIV and AIDS diagnoses

Knowledge of HIV incidence is important to formulate sensible strategies aimed at controlling the HIV/AIDS epidemic. Back-projection is one of the methods for reconstructing the HIV incidence curve from AIDS incidence data. However, because of the low risk of developing AIDS during the first few years after infection, precise estimates of HIV incidence for the recent past are unlikely if we use AIDS incidence data only. As a result there have been recent attempts to use, not only the date of AIDS diagnosis, but also to use the date of their first positive HIV test. The objective of this paper is to incorporate into back-projection the additional information provided by those individuals who have tested HIV positive but have not yet developed AIDS. This adds information on a very large number of other individuals, and provides the hope that the precision of back-projection is improved considerably. The date of a positive HIV test or an AIDS diagnosis of an individual, whichever comes first, is used in a generalized convolution equation for the purpose of back-projection. The method is illustrated by an application to Australian HIV and AIDS data. Study results show that dramatic improvement in precision is gained for estimates of HIV incidence in recent years when both HIV and AIDS diagnosis dates are used on all individuals.     

Assessing the extent of the Australian HIV epidemic from AIDS surveillance data

Abstract: Current knowledge about human immunodeficiency virus (HIV) disease is used to assess past and future trends in Australian HIV/AIDS (acquired immune deficiency syndrome) incidence, focusing on the precision with which such assessments can be made. The statistical method of back-projection is applied to reconstruct the past pattern of HIV incidence from surveillance data on AIDS incidence to June 1992. The results indicate that HIV incidence rose rapidly in the early 1980s to peak in 1983–1984, followed by a sharp decline. This finding is insensitive to plausible variations from the assumptions made, and is consistent with both success in preventive strategies and high levels of infection in a subgroup having a high probability of exposure. Cumulative HIV incidence to the end of 1987 is estimated with a 90 per cent confidence interval from 9 350 to 10 350. Estimation of the cumulative HIV incidence to June 1992 is less precise, with a 90 per cent confidence interval of 12 900 to 17 800. After adjustment for underreporting the incidence could be as high as 22 000, but only if recent infection rates, which cannot be quantified accurately, were very high. Based on data to June 1992, the estimated trend in AIDS incidence indicates 680 new cases in 1993, rising gradually to 695 in 1995. The estimated rate of increase in AIDS incidence over the recent past and near future is significantly less than that observed earlier in the epidemic. This is a consequence of both the earlier peak in HIV incidence and the effect of therapy.     

Monitoring the incidence of HIV infection in the United States

The Centers for Disease Control and Prevention maintains a national surveillance system that provides data about the HIV/AIDS epidemic for program planning and resource allocation. Until recently, incidence of HIV infection (i.e., the number of individuals recently infected with HIV) has not been directly measured. New serologic testing methods make it possible to distinguish between recent and long-standing HIV-1 infection on a population level. This article describes the new National HIV Incidence Surveillance System.     

The need for an urban HIV/AIDS policy in the United States

Urban centers in America are the hardest hit areas by the HIV/AIDS epidemic. The incidence of HIV/AIDS is higher in these areas because of high levels of poverty, sexually transmitted diseases, injection drug use, and the limited participation of urban residents in the design and delivery of health services. This article argues that a new urban HIV/AIDS policy is needed to focus on the vigorous implementation of risk reduction activities, linking HIV reduction with poverty alleviation programs, and the implementation of neighborhood health services.     

An overview of the recent trends in HIV/AIDS in the United States

This paper reviews the recent trends in the HIV/AIDS disease in the United States focusing on how the disease has matured over time and has now started to affect population segments that were not typically considered at-risk. The data reveals that HIV/AIDS levels have increased among women while it has decreased among men. HIV/AIDS has disproportionately affected the African American population while the levels have declined among whites. The case fatality rates of AIDS have declined from about 93% to 6% between 1981 and 1995. Overall the epidemic has slowed in the United States and more people affected with this disease are living longer. This can be attributed to effective treatment available and the increase in the general awareness of the disease in the US.     

Immunogenetic surveillance of HIV/AIDS

Evolutionary pressure by viruses is most likely responsible for the extraordinary allelic polymorphism of genes encoding class I human leukocyte antigens (HLA) and killer immunoglobulin-like receptors (KIR). Such genetic diversity has functional implications for the immune response to viruses and generates population-based variations in HLA class I allele frequencies and KIR gene profiles. The HIV-1 virus has relatively recently established itself as a major human pathogen, rapidly diversifying into a variety of phylogenetic subtypes or clades (A-G) and recombinants in different populations. HIV-1 clade C is the most common subtype in circulation accounting for 48% of all infections, followed by HIV-1 clades A and B which are responsible for 13% and 11% of infections in the current pandemic, respectively. Candidate gene studies of large cohorts of predominantly HIV-1 clade B but also clades C and A infected patients, have consistently shown significant associations between certain HLA class I alleles namely HLA-B*57, B*58, B*27, B*51 and relatively low viraemia. However, there is evidence that other associations between HLA-B*15, B*18 or B*53 and levels of HIV-1 viraemia are clade-specific. Recent genome-wide association studies of HIV-1 clade B exposed cohorts have confirmed that HLA-B, which is the most polymorphic locus in the human genome, is the major genetic locus contributing to immune control of viraemia. Moreover, the presence of natural killer cell receptors encoded by KIR-3DL1 and 3DS1 genes together with certain HLA class I alleles carrying the KIR target motif Bw4Ile80, provides an enhanced ability to control HIV-1 viraemia in some individuals. It is likely that rapid co-evolution of HIV-1 immune escape variants together with an adjustment of human immune response gene profiles has occurred in some exposed populations. Taken together, immunogenetic surveillance of HIV-1 exposed cohorts has revealed important correlates of natural immunity, which could provide a rational platform for the design and testing of future vaccines aimed at controlling the current AIDS pandemic.     

AIDS/HIV epidemiological surveillance in Navarra

The incidence of AIDS in the European Union has been declining since 1996 as a result, at least in part, of the use of more efficient treatments for HIV infection. The same tendency can be observed in Navarra. In 1998 the incidence of AIDS in Navarra, 75 cases per million inhabitants, was situated at an intermediate level in the ranking of Spanish autonomous communities. In the same year, the highest rates of incidence in Europe were recorded in Spain (93.3 cases per million inhabitants) and Portugal (81.8), and the lowest in Ireland and Finland, with less than 5 cases per million inhabitants. With respect to the incidence of HIV infection, 2,240 cases were diagnosed in Navarra between 1985 and December 1998. The available data indicate that at least 1,864 of these cases were resident in Navarra. The annual number of new diagnoses of HIV infection show two high points in the years 1987 and 1991, with over 200 annual cases. From 1993 onwards, a progressive decline can be observed in the annual number, with 171, 145, 19, 86 and 63 cases in the final year, 1998. The figure of over 2,000 cases of HIV infection contrast with the 694 cases of AIDS registered in this autonomous community in the same period and help to resituate the epidemic in more accurate terms. The development of AIDS in 40% of the persons with HIV infection and the death of 26% have been confirmed, although lethality has been declining in recent years. The use of intravenous drugs in 73.2% of the AIDS cases is the most frequent category of transmission. 13.4% are due to transmission by heterosexual contact and 6.1% to homosexual practices between males. Although the cases of AIDS have been declining in Navarra since 1996, the data from the microbiology laboratories and from the hospital services that treat persons with HIV infection indicate that a considerable number of new infections will continue to occur, which justifies the need for maintaining the prevention programs in order to avoid new cases of a disease whose prognosis is of such seriousness     

Estimating HIV incidence rates from age prevalence data in epidemic situations.

We present a method of estimating HIV incidence rates in epidemic situations from data on age-specific prevalence and changes in the overall prevalence over time. The method is applied to women attending antenatal clinics in Hlabisa, a rural district of KwaZulu/Natal, South Africa, where transmission of HIV is overwhelmingly through heterosexual contact. A model which gives age-specific prevalence rates in the presence of a progressing epidemic is fitted to prevalence data for 1998 using maximum likelihood methods and used to derive the age-specific incidence. Error estimates are obtained using a Monte Carlo procedure. Although the method is quite general some simplifying assumptions are made concerning the form of the risk function and sensitivity analyses are performed to explore the importance of these assumptions. The analysis shows that in 1998 the annual incidence of infection per susceptible woman increased from 5.4 per cent (3.3-8.5 per cent; here and elsewhere ranges give 95 per cent confidence limits) at age 15 years to 24.5 per cent (20.6-29.1 per cent) at age 22 years and declined to 1.3 per cent (0.5-2.9 per cent) at age 50 years; standardized to a uniform age distribution, the overall incidence per susceptible woman aged 15 to 59 was 11.4 per cent (10.0-13.1 per cent); per women in the population it was 8.4 per cent (7.3-9.5 per cent). Standardized to the age distribution of the female population the average incidence per woman was 9.6 per cent (8.4-11.0 per cent); standardized to the age distribution of women attending antenatal clinics, it was 11.3 per cent (9.8-13.3 per cent). The estimated incidence depends on the values used for the epidemic growth rate and the AIDS related mortality. To ensure that, for this population, errors in these two parameters change the age specific estimates of the annual incidence by less than the standard deviation of the estimates of the age specific incidence, the AIDS related mortality should be known to within +/-50 per cent and the epidemic growth rate to within +/-25 per cent, both of which conditions are met. In the absence of cohort studies to measure the incidence of HIV infection directly, useful estimates of the age-specific incidence can be obtained from cross-sectional, age-specific prevalence data and repeat cross-sectional data on the overall prevalence of HIV infection. Several assumptions were made because of the lack of data but sensitivity analyses show that they are unlikely to affect the overall estimates significantly. These estimates are important in assessing the magnitude of the public health problem, for designing vaccine trials and for evaluating the impact of interventions.     

Joint analysis of HIV and AIDS surveillance data in back-calculation

AIDS surveillance data are the main source of information to perform back-calculation of HIV incidence. We propose a method to incorporate additional information gained by linkage with an HIV surveillance system, containing data on the time of first positive HIV test. In this paper we generalize an earlier method that was developed to use HIV testing data available only for AIDS cases. The new method also makes use of cases with an HIV positive test who have not yet developed AIDS, typically a substantial proportion of the HIV-infected population. Furthermore, we use a more realistic model for the HIV testing rate, incorporating dependence on both time since infection and calendar time. The method makes use of an EM algorithm with generalized additive model smoothing, and is applied to data from Veneto, a region of northern Italy. Our results show that HIV incidence in Veneto peaked in the late 1980s, and decreased thereafter. Importantly, the HIV incidence estimates based on joint analysis of HIV and AIDS surveillance data are more efficient than estimates based on AIDS surveillance data alone. Our estimates also show a decreasing trend in the HIV testing rate over time, which leads to the conclusion that the interval between HIV infection and first positive test has lengthened over time. Furthermore, it is found that for infected individuals, the probability of seeking on HIV test is highest soon after infection.     

镇江市2005年艾滋病监测结果分析

目的:分析镇江市艾滋病流行现状和发展趋势,为采取有效控制措施提供科学依据。方法:采用哨点监测、自愿匿名咨询检测、重点人群筛查和专题流行病学调查等方法,收集全市艾滋病病毒感染资料和艾滋病病例报告资料。结果:2005年全市共筛查监测各类人群121 354人,检出HIV抗体阳性者31人,检出率2.25/万。通过艾滋病网络专报系统搜索外地报告本市户籍者5例,共计36例。其中男性29例,占80.6%,年龄20~39岁者占80.6%,市辖户籍占27.8%,流动人口占72.2%。传播途径经静脉吸毒占44.4%,性传播占25.0%,供血和输注血液制品占11.2%,不详占19.4%。结论:镇江市HIV流行已经由静脉吸毒人群经性乱人群向一般人群蔓延,流动人口将成为该市艾滋病传播的重要因素。应进一步加大综合监测、健康教肓、行为干预和“四免一关怀”力度。     

Models for the HIV infection and AIDS epidemic in the United States

Statistical models of the HIV infection epidemic in the U.S. which account for the observed incidence of AIDS cases in the years 1978-1987 are considered. The models assume a known distribution of times from infection to AIDS. The best model estimates that there were approximately 563,000 to 1,110,000 individuals infected in the U.S. in April 1987. These estimates do not take into account underreporting of AIDS cases. The sensitivity of the conclusions to the model's assumptions is ascertained by investigating a variety of parametric models for the infection epidemic, a variety of likely distributions for the time from infection to AIDS, and some plausible alternatives for the history of AIDS cases in the U.S.. It is concluded that there is too much uncertainty in the data and the models to be able to give highly accurate predictions of the number of people currently infected in the U.S., however, the results from the best fitting models suggest that there are less than the 1 to 1.5 million infected as estimated by the Centers for Disease Control. A Bayesian scheme is suggested for incorporating the uncertainty in the models.     

Health care seeking for HIV/AIDS among South Asians in the United States

Health-related behavior is a function of the sociocultural and environmental contexts in which it occurs. With South Asian immigrants, a comprehensive approach that focuses on community and individual factors may be more effective than an individualistic one. This article explores the factors that may influence HIV/AIDS-related health care seeking by South Asian immigrants to the United States. It focuses on South Asians from Bangladesh, India, and Pakistan. The need to involve the community in any intervention process is discussed. An understanding of the determinants of HIV-related health care seeking and behavioral change factors can help social work practitioners develop effective interventions for and with South Asian immigrants.