CDC NATIONAL AIDS HOTLINE TRAINING BULLETIN #47 - May 3, 1993
Centers for Disease Control and Prevention

1. What is the history behind the recent change in the CDC AIDS surveillance case definition?

Timeline:

5/91 - The Council of State and Territorial Epidemiologists passes a resolution recommending that CDC expand the surveillance definition for AIDS.

6/91-11/92 - CDC works with clinicians, epidemiologists, public health officials, and community groups to develop consensus on the expanded surveillance criteria.

12/18/92 - CDC publishes in the Morbidity and Mortality Weekly Report (MMWR) a document entitled "1993 Revised Classification System for HIV Infection and Expanded Surveillance Case Definition for AIDS Among Adolescents and Adults." This Report replaces the classification system and the AIDS surveillance criteria published by CDC on 5/23/86 and 8/14/87, respectively.

1/1/93 - All states and territories begin using the expanded definition for AIDS case reporting.

2. Why did CDC change the AIDS surveillance definition?

AIDS is the group of clinical conditions or laboratory markers that are indicative of severe immunosuppression due to HIV- infection. The AIDS surveillance case definition was expanded to include the laboratory markers for severe HIV disease (i.e., CD4+ count) and other clinical conditions which cause severe illness and death. CDC believes that this revised HIV classification system and expanded AIDS surveillance case definition will help to simplify the HIV classification system and AIDS case reporting process, will better categorize HIV- related morbidity, and will more accurately reflect the number of persons with severe HIV-related immunosuppression who are at highest risk for severe HIV-related morbidity and most in need of close medical follow-up. The AIDS surveillance definition does not include all persons with known HIV- infection. An estimated 1 million persons are infected with HIV in the United States.

3. What impact has the change in the AIDS surveillance definition made on cases reported to CDC since January 1, 1993?

From January 1, 1993, through March 31, 1993, state and local health departments reported 35,779 AIDS cases to CDC, representing a 204% increase in the number of cases reported during the same period of 1992 and bringing the total number of AIDS cases reported since 1981 to nearly 285,000. Most of the cases reported during this first quarter (60%) were reported under the AIDS surveillance criteria added in 1993. Of the cases meeting only these 1993-defined conditions, 89% were reported among HIV-infected persons with severe immunosuppression, 9% were reported with pulmonary tuberculosis, 1% with recurrent pneumonia, and <1% with invasive cervical cancer.

4. Did CDC expect this increase in the number of reported AIDS cases?

Yes. CDC projected that the number of persons reported with AIDS would increase by approximately 75% for all of 1993. These early effects of the expanded AIDS surveillance case definition are expected to be greater than long-term effects, and in subsequent years the increase in reported cases resulting from the expansion is projected to be approximately 10%-20% over the number that would have been reported if surveillance criteria had remained unchanged.

5. Why did the number of cases meeting the old definition also increase?

Additional cases meeting the pre-1993 AIDS surveillance definition may have been identified as part of expanded surveillance activities developed to implement the new AIDS reporting criteria. In addition, efforts to implement the expanded AIDS surveillance definition may have disrupted the timely reporting of cases meeting the definition. This may explain the longer delay in reporting for these persons in 1993 compared to that for earlier reporting periods.

6. Are the characteristics of persons reported with the 1993-added conditions similar to persons reported with pre-1993 conditions?

Yes. The age, sex, race, and mode of transmission of HIV are similar for persons reported with pre-1993 and 1993-added conditions. However, the characteristics of persons reported with AIDS may change as additional persons are reported using the 1993 surveillance case definition. CDC will continue to evaluate these trends as more information becomes available.