The United States has a comprehensive system of HIV surveillance that includes HIV case reporting and staging of disease, monitoring of HIV-related mortality, supplemental studies of behavioral and clinical indicators, and estimates of incidence and prevalence. Additional studies, such as longitudinal cohorts of HIV-infected persons, contribute to understanding of disease over time in individuals. The data highlight substantial changes in HIV and late disease stage (AIDS) incidence, prevalence, and mortality, and profound disparities across populations related to sexual behavior, drug use, race, ethnicity, geography, and socioeconomic status.
INCIDENCE AND PREVALENCE OF HIV AND AIDS
State and local governments hold legal authority for public health surveillance, including the designation of reportable conditions and reporting methods. Reporting of HIV surveillance data to the federal government is voluntary. AIDS reporting started in 1981; by 1986, all 50 states, the District of Columbia, and several US territories had instituted AIDS case reporting.1 Beginning in 1985, many states implemented HIV case reporting as part of an integrated HIV and AIDS surveillance system; although recommended by the Centers for Disease Control and Prevention (CDC) since 1999, the implementation of HIV reporting across the United States occurred at different points in time.2,3 As of 2008, all states had implemented confidential, name-based HIV reporting.
CDC's HIV surveillance system tracks new diagnoses of HIV infection and stage 3 disease (AIDS). Most cases are initially reported to state or local health departments through routine laboratory reporting of confirmatory HIV antibody, viral detection, or CD4 cell count test results. Completion of case reports occurs through provider-based reporting or follow-up by health department staff.
For 2006, it was estimated that 1.1 million people were living with HIV in the United States (95% confidence limit: 1.06 to 1.16 million), with considerable geographic variation.4 For example, AIDS diagnosis rates vary across states, ranging from 1.8 per 100,000 in Vermont to 27.7 per 100,000 in Maryland (Fig. 1A). In addition, because of higher total population and rates of AIDS in certain states, the epidemic is concentrated in certain geographic regions; 50% of reported AIDS cases in 2008 were from 5 states: New York, California, Florida, Texas, and Georgia.5 Furthermore, within states, higher numbers of cases are generally reported from urban areas (Fig. 1B).
HIV disproportionately affects different populations. HIV incidence estimates indicated that there were 56,300 new HIV infections in 2006.6 Of these new HIV infections, 45% were among blacks and 17% among Latinos (Fig. 2A); the incidence among blacks was 7 times, and among Latinos 3 times, the rate among whites. More than half (53%) of new HIV infections were among men who have sex with men (MSM); 12% were among injection drug users, 4% among MSM who inject drugs, and 31% attributable to heterosexual contact (Fig. 2B). MSM are estimated to have a diagnosis of HIV infection at a rate more than 40 times the rate among other men and among women.7
HIV surveillance data are used to estimate HIV prevalence in the United States, including the estimated number of persons infected but undiagnosed. Of the estimated 1.1 million persons living with HIV in the United States, 21% were undiagnosed and presumed to be unaware of their infection.4 The National Health and Nutrition Examination Survey is a national household-based survey that conducts interviews and testing, including for HIV infection. Data from National Health and Nutrition Examination Survey during the period 1999-2006 indicated that 0.5% of the adult population had HIV infection, with considerable disparities. The prevalence was 2.0% among blacks and 9.4% among MSM.8
MEASURES OF BEHAVIORAL AND SOCIAL RISK FOR HIV INFECTION
The National HIV Behavioral Surveillance System (NHBS) is a community-based survey that conducts interviews and HIV testing among 3 populations: MSM, injection drug users, and heterosexuals at increased risk for HIV infection. NHBS is conducted in large metropolitan statistical areas in the United States, where approximately 60% of the nation's AIDS cases had been reported.9
Risk behavior data from NHBS have shown that 47% of MSM had engaged in unprotected anal intercourse during the past year,10 and 33% of injection drug users reported sharing needles.11 Data from NHBS highlight that HIV infection is influenced by social, structural, and economic systems. In impoverished urban areas (ie, where ≥20% of residents have household incomes below the poverty level), 2.1% of heterosexual NHBS participants were infected with HIV.12 Infection was independently associated with lower household income, unemployment, lack of housing, and low education, but did not differ significantly by race or ethnicity.
Persons who do not know they are HIV infected account for a disproportionate percentage of new transmissions because they are more likely to engage in high-risk sexual behavior than persons who have learned they have HIV.13 To increase the number of persons who know their HIV status and who are, if positive, linked to clinical and preventive services early, CDC recommends offering universal routine opt-out voluntary HIV screening for all persons ages 13-64 years in health care settings and repeat annual testing for persons at high risk for HIV.14 Data from the National Health Interview Survey indicate that between 1987 and 2006, the number of persons reporting having ever been tested for HIV infection rose from 6% to 38%.15
Among MSM participating in NHBS during 2008 in 21 cities, HIV prevalence was 19% among all tested men, of whom 44% were unaware of their infection, and 28% among black MSM, of whom 59% were unaware of their infection.16 In a study of black and Latino MSM conducted in Los Angeles, New York, and Philadelphia, 17% of black and 5% of Latino MSM who did not know they had HIV tested positive.17 Among young black MSM college students and black women in North Carolina, most reported that at the time of their positive HIV test they believed they were unlikely to be infected.18,19
Late HIV diagnoses are an indicator that testing needs to reach more persons earlier. It is estimated that 32% of people diagnosed with HIV received a diagnosis of AIDS within 12 months of diagnosis.5 The median first CD4 cell count is low, between 167 and 175 cells/mm3, within 12 months of HIV diagnosis.20 However, recent reports suggest improvements may be occurring.21,22
ACCESS TO CARE AND QUALITY OF CARE
To maximize the benefit of early HIV diagnosis and treatment, patients need to have access to high-quality medical services. Receipt of care depends on prompt linkage to services and retention in care after diagnosis. A meta-analysis of studies from the mid-1990s to 2006 found that 72% of HIV-diagnosed persons in the United States entered HIV medical care within 4 months of diagnosis.23 Among persons entering care, 69% completed ≥2 visits during a 6-month interval and 59% completed ≥3 visits during a 12-month period.
Much of the morbidity and mortality benefit associated with widespread use of highly active antiretroviral therapy has been derived from the associated profound reductions in AIDS-defining opportunistic illnesses (Fig. 3).24 Since its advent in 1996, the timing of highly active antiretroviral therapy initiation has been an area of considerable interest and controversy. Recently revised US guidelines recommend initiating antiretroviral therapy at CD4 cell counts <500 cells per cubic millimeter with the option of initiating at higher CD4 cell counts.25 Evidence from a clinical trial26 and multiple cohort studies suggests that patients initiating antiretroviral therapy at higher CD4 cell counts experience improved survival27-29 and have reduced risk for non-AIDS-defining illnesses and complications and toxicities of treatment with antiretroviral drugs.26,30-33 Initiation of antiretroviral therapy at higher CD4 cell counts does not seem to increase the risk of developing antiretroviral drug resistance34 or of exhausting available treatment options and failing therapy.35
To evaluate the impact of these recommendations, researchers examined data from the Medical Monitoring Project, a national, population-based surveillance system of HIV-infected persons who receive clinical care. The project uses a 3-stage sampling design to obtain annual cross-sectional probability samples of adults receiving outpatient care for HIV infection in 23 jurisdictions. Data are collected by interview and medical record review.36 Survey data from 2007 indicated that patients with CD4 <500 cells per microliter who were not already taking antiretroviral drugs accounted for 8% of the analysis population (4% with CD4 <350 cells/uL-the previously recommended threshold-and 4% with CD4 between 350 and 499 cells/uL). Based on these data, under the current guidelines, state and local jurisdictions may need to provide treatment resources to an additional 10% of HIV-infected patients in care.37
Studies continue to demonstrate that widespread use of antiretroviral therapy since 1996 has led to sustained and continually improving reductions in morbidity and mortality among HIV-infected adults and children.38,39 In the United States, life expectancy after HIV infection increased from 10.5 to 22.5 years between 1996 and 2005, respectively.40 With improved survival on antiretroviral therapy, HIV-infected persons are increasingly affected by chronic and often preventable illnesses41-44 and non-AIDS-defining cancers45-49; further reductions in mortality and morbidity will require effective prevention and treatment of these conditions.50
Throughout the 30 years of the HIV epidemic, US surveillance systems and cohort studies have tracked many changes. HIV incidence peaked in the mid-1980s with approximately 130,000 infections per year and has decreased to approximately 56,000 infections per year more recently.6 Confidential name-based HIV reporting in all 50 states will greatly improve our ability to monitor the epidemic nationally. The first national reports on trends of diagnoses of HIV infection will be available for 2012 data, due to methods for adjusting data for reporting delays that require 4 years of experience with reporting data.5 These data will provide the clearest picture of the epidemic to date; funding opportunity announcements targeting dollars by group or geography will follow suit.
With the release of the National HIV/AIDS Strategy for the United States in July 2010,51,52 epidemiologic data will take on new importance for addressing the HIV epidemic. The constellation of surveillance systems and cohort studies provides data to monitor the epidemic and better design, implement and evaluate public health programs. The successful impact of the National HIV/AIDS Strategy will be assessed using epidemiologic data collected from these systems to measure reduced incidence, increased access to care, and improvements in health equity.
The authors acknowledge Kim Elmore for creating the maps.
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