CDC NATIONAL AIDS HOTLINE TRAINING BULLETIN #20 - December 31, 1992
Centers for Disease Control and Prevention

1. What are the changes in the classification system for HIV infection and the case definition for AIDS?

On December 18, 1992, the Centers for Disease Control and Prevention (CDC) published a revised classification system for human immunodeficiency virus (HIV) infection and an expanded surveillance case definition for acquired immunodeficiency syndrome (AIDS) among adolescents and adults in the United States.* Based on the clinical standard for immunologic monitoring of persons infected with HIV, the revised classification system includes the CD4+ T- lymphocyte measurement in the categorization of HIV-related clinical conditions and replaces the HIV classification system published by CDC in 1986. The expanded AIDS surveillance case definition includes all HIV-infected persons who have less than 200 CD4+ T-lymphocytes/ L or a CD4+ T-lymphocyte percent of total lymphocytes less than 14, or who have been diagnosed with pulmonary tuberculosis, invasive cervical cancer, or recurrent pneumonia. This new definition retains the reporting criteria listed in the 1987 surveillance definition. Beginning January 1, 1993, the expanded definition is to be used by all states and territories for AIDS case reporting.

2. Why were these changes made?

The classification system for HIV infection in adults and adolescents is a categorization of conditions associated with HIV infection. The 1986 HIV classification system was based on disease criteria only. The revised HIV classification system includes the CD4+ T-lymphocyte measurement in HIV-infected persons to establish the severity of HIV-related immune suppression. This revised system provides a framework for educating health care providers about the clinical and immunologic manifestations of HIV infection. The objectives of these changes are to simplify the classification of HIV infection, to reflect current standards of medical care for HIV-infected individuals, and to categorize more accurately HIV-related morbidity.

3. What is the AIDS case definition used for?

CDC's AIDS surveillance case definition is used to track severe HIV infection in the United States. Persons meeting the AIDS surveillance definition are reported to CDC by state and territorial health departments after all identifying information has been removed. Information from AIDS case reporting is used to monitor the AIDS epidemic in the United States and to target prevention programs and treatment services. In addition to the inclusion of HIV- infected persons with less than 200 CD4+ T-lymphocytes/ L or a CD4+ T-lymphocyte percent less than 14, the expanded AIDS surveillance case definition adds pulmonary tuberculosis, recurrent pneumonia, and invasive cervical cancer in HIV- infected persons to the 23 clinical conditions listed in the 1987 surveillance definition. The objectives of this expansion are to reflect more accurately the number of persons with severe HIV-related morbidity and immunosuppression and to simplify the reporting process. The addition of the three clinical conditions reflects their documented or potential importance in the HIV epidemic.

4. Why is the number of CD4+ T-lymphocytes so important?

The CD4+ T-lymphocyte, which coordinates a number of important immunologic functions, is the primary target for human immunodeficiency virus. HIV infection results in the loss of these functions and causes progressive impairment of the immune response. As the number of CD4+ T-lymphocytes decreases, the risk and severity of many illnesses increase.

In addition, measures of CD4+ T-lymphocytes are currently used to guide clinical and/or therapeutic actions for HIV- infected persons.

5. What impact is are these changes expected to have?

The expanded AIDS surveillance case definition is expected to have a substantial impact on the number of reported cases. The immediate increase in case reporting will be largely attributable to the addition of severe immunosuppression to the definition; a smaller impact is expected from the addition of HIV-infected persons with pulmonary TB, recurrent pneumonia, and invasive cervical cancer, since many persons with these diseases will also have less than 200 CD4+ T-lymphocytes/ L. If AIDS surveillance criteria had remained unchanged, approximately 50,000-60,000 reported AIDS cases would have been expected in 1993. Based on current levels of HIV infection and CD4+ T-lymphocyte testing, CDC estimates that the expanded definition could increase cases reported in 1993 by approximately 75%, resulting in perhaps a total of 85,000 to 90,000 cases reported in 1993. In subsequent years, the effect of this expansion on the number of reported cases is expected to be much smaller.

6. Will these changes affect the confidentiality of AIDS case report?

The confidentiality of AIDS case reports, including laboratory reports of HIV test results, CD4+ T-lymphocyte test results, and medical records under review by health department staff, is of critical importance to maintaining effective AIDS surveillance. CDC and state health departments have procedures and policies to maintain confidentiality and security of HIV/AIDS surveillance data.

7. What about insurance or Social Security benefits, will these be affected by the new classification system?

The revised HIV classification system and the expanded AIDS surveillance case definition are intended to meet the needs of state public health notifiable disease reporting systems.

The criteria for case reporting were not developed for purposes of determining insurance reimbursement or eligibility for disability benefits. The revised surveillance case definition does not alter the criteria used by the Social Security Administration in evaluating claims based on HIV infection under the Social Security disability insurance and Supplemental Security Income programs. The Social Security Administration has recently proposed a new method for the evaluation of HIV infection and criteria to determine eligibility for disability. Other organizations and agencies providing medical and social services should develop eligibility criteria appropriate with the services provided and local needs.

* This document was published as part of the Morbidity and Mortality Weekly Report Recommendations and Reports series. Single copies of the document will be available in mid-January from the CDC National Prevention Information Network, P.O. Box 6003, Rockville, MD 20849-6003; telephone (800) 458-5231.

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