CLINICAL AND EPIDEMIOLOGIC IMPLICATIONS OF THE CENTERS-FOR-DISEASE-CONTROL WORLD-HEALTH-ORGANIZATION RECLASSIFICATION OF AIDS CASES

Objective: To establish whether various accepted and proposed AIDS def initions have clinical and biological validity: because the Centers fo r Disease Control and Prevention (CDC) and World Health Organization ( WHO) reclassifications of AIDS are important not only for describing t he epidemiology of HIV disease but also to individual patients. Settin g: Regional Infectious Diseases Unit, City Hospital, Edinburgh, Scotla nd, UK. Patients: We analysed the disease progression of 532 HIV-serop ositive individuals seen at the City Hospital, Edinburgh, up to the en d of July 1991. Main outcome measures: Annual numbers of potentially r eportable cases from the Edinburgh City Hospital Cohort according to t hree proposed AIDS case definitions based on: (1) first lymphocyte cou nt less-than-or-equal-to 1000 x 10(6)/l; (2) first CD4 cell count less -than-or-equal-to 200 x 10(6)/l; or (3) first of two consecutive CD4 c ell counts less-than-or-equal-to 200 x 10(6)/l. Lifetables to death (i rrespective of cause) from month of satisfying the above case definiti ons, and proportion of patients who satisfied each definition in their calender year of enrolment in the cohort are reported. Results: There is a threefold increase in patients in the Edinburgh City Hospital Co hort defined as having AIDS under the 1987 and the proposed 1992 CDC d efinitions-a substantial change for patients and epidemiologists alike . That they are describing different immunodeficiency states is clear from lifetable analysis, which reveals median survivals of 20 and 50 m onths under the 1987 and the proposed 1992 AIDS definitions, respectiv ely. For epidemiological purposes, redefinitions based on the WHO prop osed classification of HIV disease using either a lymphocyte count les s-than-or-equal-to 1000 x 10(6)/l or a CD4 cell count less-than-or-equ al-to 200 x 10(6)/l are broadly interchangeable. They are not equally effective for monitoring individual progression (CD4 cell count is sup erior). Both, for different reasons, lack biological plausibility. Con clusions: We therefore suggest that the stricter, biologically more pl ausible, case definition used in Scotland of two consecutive CD4 cell counts of less-than-or-equal-to 200 x 10(6)/l [CD4(200) (x 2)] should be adopted-not as a new definition of AIDS, but as an additional impor tant state of severe HIV-related immunodeficiency (SHRID). Median surv ival under the CD4(200) (x 2) case definition was 40 months in the Edi nburgh cohort. We have illustrated differences in CD4(200) case ascert ainment between injecting drug users and other HIV-infected patients i n the Edinburgh City Hospital Cohort. We recommend that surveillance c entres should ascertain date of first immunological monitoring as well as date of SHRID diagnosis in order to identify differential case asc ertainment.