• Targeting Prevention to Vulnerable Adolescents
• Epidemiology of Adolescent HIV and AIDS in U.S.
• Vulnerability of Female Youth to HIV
• Rates of HIV Testing Among Youth
• Specificity of HIV Surveillance Data
• Adolescent Trials Network (ATN) Protocol 016
• Summary

Adolescence is a stage of life typically characterized by good health, with healthcare encounters focused on health maintenance and issues surrounding prevention of STDs, drug use, and unwanted pregnancy. Adolescent health care providers in geographic regions hard hit by HIV are now faced with two important trends. First, a large cohort of youth infected by birth and sustained by HAART is coming of age and in need of specialized medical care, including counseling and services to address their reproductive health choices. Secondly, uninfected youth are entering a phase of their lives in which their behavior choices, coupled with social vulnerabilities that might not be apparent to the health care provider, could dramatically increase their risk of HIV-infection. To date, high rates of HIV have been described in young men who have sex with men, young injection drug users, and homeless or runaway youth who engage in these transmission behaviors. Hetero-sexually acquired HIV among female youth is a growing problem, but identifying specific characteristics of those at risk remains a challenge. The aim of the newly organized NIH-funded Adolescent Trial Network (ATN) is to develop effective methods of enhanced case finding for HIV-infected youth and to develop and test prevention interventions for the most vulnerable youth. This article will discuss rates of HIV testing among youth, surveillance data on HIV-infection among adolescents in the U.S. as well as the limitations of those data, and Protocol 016 of the ATN, which is designed to systematically identify infected and at-risk youth in highly impacted U.S. cities.

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Targeting Prevention to Vulnerable Adolescents

Effective primary HIV prevention trials should target individuals at significant risk for becoming infected with HIV. A means to identify these individuals is to examine the characteristics of recently infected individuals. However this approach is limited by ascertainment bias. Testing programs systematically miss infected subpopulations of individuals. In addition, testing programs fail to collect or make available data about infected individuals beyond age, race, gender, residential zip code area, and route of transmission. For example, while age, race, and residential zip code area provide information on those least likely to be infected with HIV, these variables do not provide accurate information on which individuals are in fact infected.

Concerns about these limitations may be purely academic in regions and populations where the prevalence of HIV is relatively high, as in the case of African-American men who have sex with men in large urban U.S. cities or among women of childbearing age in certain Sub-Saharan African countries. However these limitations may be profound when targeting prevention efforts at heterosexual adolescent females in the U.S. The relatively low prevalence of infection among adolescent girls, even those of color residing in impoverished communities, means that in order for prevention programs to be cost effective, policy makers and programs need to stratify the populations further than what current testing coverage and epidemiologic data can support.

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Epidemiology of Adolescent HIV and AIDS in U.S.

Cumulative AIDS cases for younger age groups reported to the CDC through 2000 by probable transmission category are shown in the table above. Comparative case rates of HIV-infection for 34 U.S. regions with HIV reporting requirements are shown for males and females by age strata in the figure below. In 2000 alone, there were 1688 cases of AIDS reported among 13-24 year-olds, 729 of whom were female. The majority (75%) of the female cases was among 20-24 year-olds and was attributed to heterosexual contact. Forty percent of female cases among 13-19 year-olds in 2000 was due to heterosexual contact, and in 51% the risk was “not reported or identified,” an exposure category often equated with heterosexual contact. The percentages of female cases among 20-24 year-olds assigned to these two exposure categories are not much different than those seen among 13-19 year olds: 47% and 40%, respectively. In contrast, only 9% and 25% of male cases among 13-24 years olds are attributed to heterosexual contact or unidentified/unreported risk.

The most recent data available on racial/ethnic distribution of female adolescent AIDS cases are from 1998. These data reveal that most female adolescent cases occurred among racial/ethnic minorities. In 1998, 447/688 (65%) female AIDS cases among 13-24 year olds were black, not Hispanic, 110/688 (16%) were Hispanic, and 123/688 (18%) were white, not Hispanic.

A review of incident HIV-infection data in the U.S. reveals demographic and exposure patterns similar to those seen with AIDS data. In 2000, 38% and 57% of female cases among 13-19 year-olds were attributed to heterosexual contact and unidentified risk, respectively. The percentage of female cases among 20-24 year-olds assigned to those two exposure categories were 38% and 53%, respectively. While surveillance data are not available for incident HIV cases by age, gender, and race/ethnicity annually, cumulative HIV cases through December 2000 show that the majority of HIV cases among 13-19 year-olds and among 20-24 year-olds occurred among black, non-Hispanic youth: 2320/3167 (73%) and 4284/6407 (67%), respectively.

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Vulnerability of Female Youth to HIV

Sexually active female teenagers may be biologically more susceptible to HIV acquisition than older women for several reasons. They tend to have the highest age-specific rates of both gonorrhea and chlamydia, infections that cause cervical inflammation, and may increase the relative risk of acquiring HIV 2-3 fold. Independent of other STDs, the less mature cervix of an adolescent commonly has larger areas of cervical ectopy than that of a more mature woman. Increased cervical ectopy has been associated with increased HIV acquisition in several reports [Moss GC et al. JID 1991;170:313]. Age-discrepant sexual relationships (i.e., female teens having much older sex partners) have been associated with higher rates of teen pregnancy, STDs, as well as HIV acquisition among teen girls [MMWR September 29, 2000 / 49(38);861-4].

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Rates of HIV Testing Among Youth

There is growing evidence that many youth are not accessing or receiving HIV testing, which may be contributing to an ascertainment bias in surveillance data. In a study of Massachusetts households, adolescents 16 to 19 years of age completed an anonymous telephone survey. Only 127/567 (22%) had been tested for HIV. Recently, the CDC reported on the rate of HIV testing among racial/ethnic minorities. The findings were based on results from the 1999 National Health Interview Survey (NHIS), an annual household based survey of U.S. non-institutionalized residents 18 years and older. The survey found that approximately 30-40% of the population had ever been tested for HIV but that less than 20% were tested in last year. Assuming that recent testing is the better proxy for rates of testing among youth, since many youth are newly sexually active, we can conclude that rates of testing among youth are low. A final indication of the low rates of HIV testing among youth comes from the surveillance data themselves. Given the total number of AIDS cases diagnosed in 1998 among 25-39 year-old women (5666) and the estimated time that it takes to develop AIDS after initial infection, the low number of youth reported with HIV during the same year (1300), suggest poor rates of HIV testing of female youth.

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Specificity of HIV Surveillance Data

An advantage of local surveillance data over national data is that it often contains information about the geographic location of the infected person’s residence. In some cities this information is collected at the level of the zip code or census tract, while in other cities it is collected at the level of the street address. This information is useful for selecting neighborhoods where higher numbers of infected persons reside. However, this information may not be useful for finding HIV-infected and at-risk youth.

Few female youth residing in the neighborhoods with high rates of adolescent female HIV are in fact infected. Furthermore, evidence suggests that not all youth residing in these neighborhoods are at equal risk. This is particularly true for adolescent females, where the best estimate of neighborhood HIV prevalence was between 0.05% and 2.0%, based on data from local adolescent medicine clinics and community based organizations participating in a marketing campaign to get youth tested for HIV. In contrast, the prevalence of HIV among men who have sex with men tested at local STD clinics are greater than 20%.

Published data from the REACH study suggest that there are important behavioral differences between HIV-infected and -uninfected female youth from similar communities and similar demographic characteristics [Wilson et al. J Adolesc Health 2001 Sep;29(3 Suppl):8-18; Vermund et al. J Adolesc Health 2001 Sep;29(3 Suppl):49-56]. The REACH Study was an observational study involving HIV-infected and -uninfected high risk 12-18 year-olds recruited from adolescent medicine clinics in the U.S. between 1996 and 1999. At entry, all participants completed a demographic and behavioral survey. The study found that while there were many similarities between infected and uninfected participants with regard to race and ethnicity, numbers of recent sex partners, and rates of gonorrhea and chlamydia (38% vs 35%), the HIV-infected girls were more likely to have dropped out of school (29% vs 16%) or to have older sex partners. Identifying girls at highest risk for choosing older male sex partners, particularly ones at high risk for HIV, may be very important in designing effective HIV prevention interventions for female youth.

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Adolescent Trials Network (ATN) Protocol 016

Given the limitation of the current surveillance data, the ATN has developed and is now implementing ATN Protocol 016. A long-term goal of the two-year ATN Protocol 016 is to develop the capacity to identify, test, and enroll youth at highest risk for HIV-infection into prevention trials in several cities with high prevalences of HIV-infection, including Miami, Los Angeles, New York, Washington DC, Baltimore, and Philadelphia. The study may eventually expand to include Chicago, Boston, San Francisco, and Puerto Rico. The first phase of this protocol grew out of the growing appreciation for the limitation of current local surveillance data. The specific aims are:

1. To characterize epidemiology of adolescent/young adult STDs and HIV in each city using existing local surveillance and published data;
   


2. To interview community partners and HIV-infected youth from high prevalence neighborhoods to find out about community-based organizations and venues such as housing projects, schools, bars, clubs, street corners, and parks where youth at high risk communities could be recruited for HIV prevention projects;
   


3. To set up temporary HIV counseling, testing and referral services at selected sites to demonstrate capacity to identify infected and high risk uninfected youth. The second phase of ATN 016 will build on these partnerships to adapt interventions to local requirements and implement studies in an array of youth-focused venues.
   

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Summary

Providing effective HIV treatment and prevention services to adolescents has emerged as a significant issue in many areas of the U.S. hard hit by HIV. Young males with same sex contact, young injection drug users, and runaway youth are all at high risk for HIV, but females appear to acquire the larger proportion of HIV as young teens, and their risk characteristics are poorly understood. A particular challenge in HIV prevention is to identify the teenage girls at highest risk for HIV acquisition and to develop and implement effective prevention interventions.

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