Applying Public Health Principles to the HIV Epidemic — How Are We Doing?

Table 1. Table 1. Epidemiologic Trends in HIV Infection in the United States, 2003 and 2012–2014.

In 2012, an estimated 1.2 million people in the United States were living with HIV infection (Table 1)³ — an increase of more than 20% over the previous decade, attributable to continued new infections and a 36.5% decrease in deaths related to the acquired immunodeficiency syndrome (AIDS).^3-5,16,17 Reported new diagnoses of HIV infection have decreased overall, but there are large disparities among groups; new HIV infections are increasingly concentrated among gay men and younger men. Between 2003 and 2014, the numbers of diagnoses of infections associated with injection-drug use and heterosexual contact decreased by approximately 70% and 40%, respectively. However, between 2003 and 2014, diagnoses increased by 5% among all men who have sex with men, in whom more than two thirds of all diagnoses now occur, and more than doubled among young gay and bisexual men.^4,5 Blacks continue to account for nearly half of all diagnoses each year, most among gay and bisexual men; the proportion of diagnoses among Hispanic Americans, Asian Americans, and American Indians or Alaska Natives has increased, and the number of diagnoses among people 13 to 24 years of age increased by 43%, also mostly among gay and bisexual men.¹⁸

Anal intercourse without a condom accounts for the overwhelming majority of infections among men who have sex with men and a substantial proportion of infections acquired heterosexually by women,^19,20 and the proportion of gay and bisexual men engaging in anal sex without a condom increased between 2005 and 2011.¹³ Some gay and bisexual men may believe that they are having sex only with people of the same serostatus as theirs, but such assumptions are often incorrect.²¹

The rate of opiate addiction has increased in diverse U.S. populations, and more than 60% of people who inject drugs report sharing injection paraphernalia.¹⁴ An HIV outbreak in Scott County, Indiana, in 2014 and 2015 associated with injection use of prescription opiates resulted in 181 cases of HIV infection in less than 12 months in a town with a population of 4300 — one of the highest incidence rates ever documented.¹⁵ Given increases in opioid prescribing and addiction, many U.S. communities may be vulnerable to similar outbreaks.

Effective public health action depends on timely, accurate, complete surveillance. All jurisdictions now require name-based HIV reporting. As of 2014, the 42 states (plus the District of Columbia) where approximately 90% of HIV-infected people are thought to live require that all CD4+ T-cell counts and results of viral-load testing be reported to the health department.³ However, many health departments do not act on surveillance results in time to stop transmission, nor do they prioritize collection, analysis, and use of data necessary to track and improve critical outcomes. Diagnosis of acute HIV infection and diagnosis occurring late in the course of infection represent sentinel health events; the former indicates recent transmission, with increased risk of spread, and the latter indicates delayed detection, with increased risk of premature death. Immediate reporting by clinicians and laboratories and rapid investigation, follow-up, and service provision to affected persons and communities should be, but is not yet, the standard response.

Investigations that use molecular epidemiology can help identify chains of transmission that can be interrupted by ART. Even without molecular epidemiologic evidence, prompt diagnosis, case interviews, and partner services can provide sufficient information for action. Use of traditional and new data sources — including data on diagnoses of HIV infection, primary and secondary syphilis cases, rectal gonorrhea cases, rectal chlamydial infections, and indicators of injection-drug use, as well as social media and (if patient confidentiality is safeguarded) electronic health records — can help in identifying and stopping microepidemics.

Health departments and clinicians have made considerable progress in improving early diagnosis of HIV infection. More sensitive laboratory tests make earlier detection possible and permit diagnosis of acute HIV infection,⁷ which is associated with higher viral loads and greater infectivity than is long-standing infection.²² Although not yet universally available to health care providers, the newest tests can identify new infections within a few weeks after transmission. The Centers for Disease Control and Prevention (CDC)²³ and the U.S. Preventive Services Task Force²⁴ recommend screening all adults and adolescents for HIV infection at least once, whether or not clinicians perceive that a patient is at risk, and repeat screening at least annually for people at high risk. CDC guidelines note that sexually active gay and bisexual men may benefit from testing as often as every 3 months; regular testing can identify infection promptly and facilitate identification and interruption of transmission chains. Rates of HIV testing have increased overall and particularly among high-risk populations; the proportion of high-risk gay and bisexual men who are aware of their HIV status increased from 59% to 77% between 2008 and 2014.

With increased testing, the number of people estimated to have undiagnosed HIV infection in the United States has decreased by nearly 40%, from approximately 250,000 in 2003^2,16 to approximately 156,000 in 2012³ — numbers that represent 25% and 13%, respectively, of Americans living with HIV infection.^2,3 But the proportion is more than 40% among 18-to-24-year-olds and more than 25% among 25-to-34-year-olds.³ The proportion of people who received a diagnosis of HIV infection late in the course of their infection (i.e., in whom AIDS developed within 3 months after the diagnosis of HIV infection) has decreased by nearly 30% since 2003,^3,25 although more than 20% of people who received a diagnosis of HIV infection in 2013 received the diagnosis late.³

A core intervention to stop transmission of communicable disease is the identification, notification, counseling, and testing of partners, with prompt linkage of infected partners to treatment in order to both improve their health and reduce further transmission. Partner services identify people with undiagnosed or diagnosed HIV infection who are not receiving care. Health departments play a key role in partner services: as compared with health care providers, disease-investigation specialists in the New York City Health Department elicited information about partners from a higher proportion of index-case patients (51% vs. 18%), elicited information about more partners per patient (0.87 vs. 0.22), and notified a higher proportion of named partners (70% vs. 48%).²⁶

Despite the importance of these services, interviews to elicit names and contact information of partners were documented to have been conducted with only about half the people who received a diagnosis of HIV infection in 2014, and patients who named partners named relatively few. Although increasing the number of partners named, tested, and linked to services can be difficult, especially in the context of anonymous sexual encounters, partner notification and testing of people in patients’ social networks, in part through the use of Internet and mobile technology (with appropriate safeguards), can help public health, clinical, and community-outreach workers find newly infected and highly infectious people and get them treatment, improve their health, and stop transmission.²⁷

Figure 1. Figure 1. Percentage of HIV-Infected People at Each Stage of the HIV Care Continuum, United States and Puerto Rico, 2012.

National HIV Surveillance System data were used to estimate the number of people 13 years of age or older who were living with diagnosed or undiagnosed HIV infection (prevalence) in the United States at the end of 2012. Data from the Medical Monitoring Project were used to estimate the number of people 18 years of age or older who received medical care for HIV infection between January and April 2012, the number who received prescriptions for antiretroviral treatment (ART), and the number whose most recent viral load in the previous year was undetectable or less than 200 copies per milliliter.

Effective public health and clinical programs are accountable for outcomes of the treatment of every patient.²⁸ On the basis of randomized, controlled studies, guidelines for the treatment of HIV infection now recommend ART for all HIV-infected people.⁸ Treatment, ideally leading to viral-load suppression, benefits the infected person and interrupts transmission, but in 2012, only an estimated 39% of HIV-infected people in the United States were receiving medical care for HIV infection, 36% had been prescribed ART, and 30% had documented viral suppression (Figure 1).³

Figure 2. Figure 2. Percentage of People Living with HIV and Percentage of HIV Transmissions at Each Stage of the Care Continuum, United States and Puerto Rico, 2012.

National HIV Surveillance System data were used to estimate the number of people 13 years of age or older who were living with diagnosed or undiagnosed HIV infection (prevalence) in the United States at the end of 2012. Data from the Medical Monitoring Project were used to estimate the number of people 18 years of age or older who received medical care for HIV infection between January and April 2012, the number who received prescriptions for ART, and the number whose most recent viral load in the previous year was undetectable or less than 200 copies per milliliter. The percentage of transmissions from each group was estimated by applying transmission rates from Skarbinski et al.³⁰ to 2012 surveillance data. There were about 10,000 transmissions from people with undiagnosed HIV infection, 31,000 from those with diagnosed infection who were not in care, 900 from those in care but not prescribed ART, 1300 from those prescribed ART but without viral suppression, and 1500 from those with viral suppression.

Although rates of treatment and viral suppression are improving and documented rates may underestimate actual rates,²⁹ hundreds of thousands of people with diagnosed HIV infection are not receiving care or ART; these people account for most new HIV transmissions in the United States (Figure 2). The greatest loss of patients in the HIV continuum of care occurs between diagnosis and engagement in medical care. Updating of published estimates³⁰ suggests that it is likely that more than 90% of transmission currently comes from people with diagnosed infection who are not retained in care (69%) and people whose infection has not been diagnosed (23%).

For uninfected persons who engage in high-risk behavior, ART (preexposure prophylaxis) can substantially reduce the risk of acquiring HIV infection through sexual or needle exposure³¹; its effectiveness correlates directly with the level of adherence.¹² Preexposure prophylaxis is likely to have the greatest effect among people at very high risk for infection, among whom the number who need to be treated for 1 year to prevent one HIV infection may be as low as 13.³²

Core interventions for the control of communicable disease are prompt diagnosis, systematic partner notification and follow-up, and accountability for treatment of all patients. Working together, health care providers, clinical systems, and public health and community organizations can identify people with newly and previously diagnosed HIV infection, provide care and ART as soon as possible with the goal of suppressing their viral load, and keep them in care continuously.

An estimated 45,000 new HIV infections occur each year in the United States, about 30,000 transmitted by patients with diagnosed infection who are not receiving care and about 10,000 by people with undiagnosed infection (Figure 2). It is possible to improve early diagnosis further by implementing intensive testing (particularly in demographic and geographic groups with recent transmission), improving partner notification, and testing people in the social networks of HIV-infected people. With improvements in detection over the past decade, it is now even more important to improve rates of initiation and continuation of treatment — to fill the biggest current gap in the care continuum and reduce transmission substantially. Targeted preexposure prophylaxis in people at highest risk can further reduce the number of new infections.

We now know that treatment of HIV infection is most effective when started early and continued throughout life but face challenges that are familiar from other chronic, often asymptomatic diseases: patients who feel relatively well are reluctant to initiate or continue treatment that may have or be perceived to have adverse effects. The situation is further complicated by the stigma associated with HIV infection and HIV risk behaviors and the disproportionate social, drug-addiction, and economic challenges faced by people living with HIV infection.

Jurisdictions throughout the United States and elsewhere³³ that have implemented public health principles have documented encouraging progress in reducing new infections. San Francisco, for example, increased rates of testing (including for recent and acute infection), partner notification, linkage or reengagement in care, and treatment of all HIV-infected people; as a result, virologic suppression has been achieved in a greater proportion of HIV-infected patients.^34-38 These initiatives plus preexposure prophylaxis were associated with a 40% decrease in reported new infections between 2006 and 2014, even though the rate of condomless sex among gay and bisexual men remained high and may have increased.³⁹ The New York City Health Department provides individual-level support to link patients to treatment and reengages patients who are not receiving care to reinitiate ART.^40,41 Rates of viral-load suppression have increased steadily, and between 2006 and 2013, the number of reported new infections decreased by 32%.^40,42

Scientific and policy advances over the past decade have provided more effective tools for preventing HIV infection and improving outcomes among infected people. The challenge now is to increase integration of health care and public health efforts in order to use these new tools to greatly reduce new infections (see the Supplementary Appendix, available with the full text of this article at NEJM.org). Momentum has been generated by the recently updated National HIV/AIDS Strategy, which includes a goal of viral-load suppression in 80% of people with diagnosed infection, an executive order to improve the continuum of care, increased access to health insurance coverage through the Affordable Care Act, and a global focus on detection, treatment, and viral-load suppression.^43-45

Advocacy by and for people living with HIV infection has accelerated drug development and approval and empowered patients and communities. Increasingly, public health principles are being implemented to stop the HIV epidemic, and the rate of new infections appears to be declining despite the facts that more people are living with HIV infection and that rates of high-risk behaviors are stable or increasing. Yet much more needs to be done, such as increased use of testing, including of the partners of infected people and others in their social networks to rapidly identify recent infections; targeted preexposure prophylaxis for key high-risk groups; and, most important, treatment initiation, continuation, or resumption in many more infected people.

The combination of patient empowerment, community engagement, clinical excellence, and public health focus on outcomes and impact could make management of HIV infection a model for combating other chronic diseases. In another 10 years, scientific advances and further implementation of public health principles could substantially reduce the number of new HIV infections in the United States.