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Surveillance refers to the many and varied systems used to track the incidence (new occurrences) and prevalence (total existing cases) of a particular disease. AIDS surveillance systems are used to track HIV infections, AIDS cases, opportunistic infections, and other data. The term is also often used to refer to policies and programs concerning the accessibility and requirements for HIV testing.

From almost the beginning of the epidemic, AIDS surveillance has been a complex and controversial subject, with advocates, public health officials, and government agencies often differing on such issues as named reporting for HIV infection, partner notification, and testing of pregnant women.

Reporting of AIDS cases has been used as the primary AIDS surveillance tool since the epidemic was identified in 1981. States report the names and demographic information of people diagnosed with AIDS to the federal Centers for Disease Control and Prevention (CDC), where national figures on the AIDS epidemic are tracked. Though AIDS surveillance is often referred to as the "gold standard" for disease surveillance, it is nonetheless also recognized as an incomplete representation of the epidemic in America. Newly diagnosed cases of AIDS can only tell epidemiologists when people are transitioning from asymptomatic HIV disease to full-blown AIDS. AIDS case reports do not capture information about the incidence of new infections--information that could greatly assist prevention planners with designing and targeting prevention resources.

With the advent in the late 1990s of powerful new AIDS treatments, called highly active anti-retroviral therapy (HAART), the limits of AIDS reporting became even more pronounced. With increasing numbers of people receiving early treatment for HIV and forestalling progression to AIDS, reporting of AIDS cases became an increasingly imprecise representation of the epidemic.

In response, many states began moving toward reporting HIV diagnoses in addition to AIDS case reporting. Communities and health officials continue to debate whether names should be used in these reports (as they are with AIDS case reports) or whether some other system, such as unique identifiers, can yield data of sufficient quality. Some AIDS advocates argue that using names to report HIV cases will scare many people from seeking testing for fear that reporting of their HIV status will lead to discrimination, particularly those at highest risk of infection (gay men, minorities, drug users).

According to the CDC, as of November 1, 1999, a total of 34 states and the U.S. Virgin Islands had implemented HIV name-based case reporting, and four states and Puerto Rico were reporting HIV cases using a coded identifier. Washington State had a hybrid system in which names are initially reported and then converted to codes.

In December 1999, the CDC issued guidelines that recommend that "all states and territories conduct case surveillance for HIV." The guidance reviews a variety of studies on name-based and unique-identifier systems of reporting, and concludes that name-based systems have several advantages. The CDC guidance "advises that state and local surveillance programs use the same confidential name-based approach for HIV surveillance as is currently used for AIDS surveillance nationwide." (With confidential reporting, a person's name is "confidentially" reported to public health authorities; with anonymous testing, the person being tested never provides his or her name, and no name is sent to authorities.) In making this recommendation, the CDC noted that some states have adopted, and others may elect to adopt, coded case identifiers for HIV reporting, and that CDC will provide technical assistance to all state and local areas regardless of the system they choose.

Laws concerning HIV testing and surveillance were affected by reauthorization of the Ryan White CARE Act in 2000. In the past, funding allocations for this and other federal AIDS programs were based on AIDS data. With growing awareness of the limitations of these data, the new law requires that HIV case data be incorporated into the case count for local and state jurisdictions in 2005 and thereafter unless it is determined that HIV case data are not yet available throughout the country.

In addition, the reauthorized CARE Act created incentives for states to move towards HIV name reporting and partner notification programs. The Act established a new $30 million authorization to enhance partner notification services in states. To receive these funds, states must implement partner notification programs and reporting of people who test HIV positive in a manner recommended by the CDC. The law also states that preference for grant funds through CARE will be given to states that have HIV reporting systems that are "sufficiently accurate and reliable." The reauthorized CARE Act also directed the Institute of Medicine to conduct a study on the ability of state HIV surveillance systems to provide adequate and reliable information on new HIV diagnoses. Some advocates are concerned that these new incentives for name-based reporting will lead more states to use a name-based system, ultimately driving more people away from HIV testing.

The AIDS case definition used for surveillance in the United States was updated by the CDC in 1992. Initially, the definition was based almost exclusively on the diagnosis of one or more "defining illnesses," i.e., opportunistic infections that were unique to AIDS. However, advocates argued that this resulted in undercounting of women, whose AIDS-related illnesses were not unique to AIDS (e.g., cervical cancer and chronic dysplasia). This was particularly problematic because many government programs based their eligibility on an AIDS diagnosis; thus, many women were dying of AIDS without qualifying for any AIDS-related services. The new definition added CD4 T-cell counts, a common marker for assessing AIDS-related immune system damage. The formal AIDS diagnosis now includes all HIV-infected adults and adolescents with a CD4 T-cell count below 200 or who have been diagnosed with pulmonary tuberculosis, invasive cervical cancer, recurrent pneumonia, HIV encephalopathy, chronic isosporiasis, disseminated histoplasmosis, wasting syndrome, or other conditions.

Outside of the United States, many countries use one of two World Health Organization (WHO) case definitions for AIDS. The WHO "AIDS surveillance case definition" is recommended in cases where there is limited access to HIV serology testing. It defines AIDS (for adults or adolescents over 12 years of age) as having at least two of the "major signs" and at least one of the "minor signs" of the disease. Major signs include weight loss equal to 10 percent or more of body weight; chronic diarrhea for over one month; and prolonged fever for over one month. Minor signs include persistent cough for over one month; history of herpes zoster; chronic progressive or disseminated herpes simplex infection; and generalized lyphadenopathy. The presence of Kaposi sarcoma or cryptococcal meningitis is also sufficient for an AIDS diagnosis under this definition.

The WHO "expanded" case definition of AIDS is recommended for use in situations where HIV serology is available. It defines the disease as testing positive on the HIV antibody test and having one or more of the following conditions: 10 percent or greater loss of body weight, with diarrhea or fever; cryptococcal meningitis; pulmonary or extrapulmonary tuberculosis; Kaposi sarcoma; neurological impairment sufficient to prevent independent daily activities not known to be due to a condition unrelated to HIV infection; candidiasis of the esophagus; clinically diagnosed life-threatening or recurrent pneumonia; or invasive cervical cancer.

Partner notification or "contact tracing" is a traditional public health tool used to identify and contact individuals who may have been exposed to an infectious agent, such as HIV or another STD. Partner notification for HIV has long been controversial and some have argued that contact tracing will compromise confidentiality and discourage people from seeking HIV-related testing and care through health departments.

In 1998, the CDC issued guidance on HIV partner counseling and referral services (PCRS). It defines the goals of PCRS as providing services to HIV-infected persons and their sex and needle-sharing partners so they can avoid infection, or, if already infected, preventing transmission to others, and helping partners gain earlier access to counseling, testing, medical evaluation, and treatment. The new CDC guidance avoids mandating the specifics of PCRS programming, choosing to leave program planning and development to state and local entities. The CDC plan also emphasizes the importance of developing an atmosphere of trust with people with HIV and the community as a whole.

More recent legal changes may affect the design and implementation of partner notification programs. The Ryan White CARE Act, reauthorized in 2000, requires programs receiving Title III funds to inform clients during posttest counseling that "it is the duty of infected individuals to disclose their status" to partners.

Rates of HIV infection in newborns fell over the last decade as voluntary HIV testing and AZT treatment of HIV-infected pregnant women were implemented across the country. In 1999, the Institute of Medicine issued a study that stated that HIV testing of pregnant women should be made a routine component of prenatal care. Under this policy, women would be informed that an HIV test is being conducted and they would retain the right to refuse to be tested.

In 1999, the American Academy of Pediatrics and the American College of Obstetricians and Gynecologists endorsed universal HIV testing of all pregnant women. Under the policy proposal, women would be given "notification" that they were being tested, but written consent for testing would not be required. The AIDS Alliance for Children, Youth and Families raised concerns about the policy recommendations, noting that, if enacted, "pregnant women would be the only group that could be tested for HIV without the benefit of pre-test counseling or affirmative informed consent."

In October 2000, the CDC issued draft recommendations on HIV testing or screening of pregnant women. The recommendations "emphasize HIV testing as a routine part of prenatal care and strengthen the recommendation that all pregnant women be tested for HIV." In issuing the guidelines, the CDC noted that 300 to 400 infants are still born HIV infected each year in the U.S.

Legislation reauthorizing the Ryan White CARE Act in 2000 created incentives for testing of newborns. The Act authorized a $20 million program that will be available annually to states with a mandatory testing requirement for all newborns or for newborns for whom the mother's HIV status is unknown, or states demonstrating the most significant reductions in rates of perinatal HIV transmission. The proportion of these funds dedicated to states with mandatory testing requirements increases over time.