CD4 SURVEILLANCE IN SCOTLAND - PERSPECTIVES ON SEVERE HIV-RELATED IMMUNODEFICIENCY

Objective: To analyse factors that influence the following: the square root of first CD4 cell count; which individuals are severely immunode ficient at or before the start of monitoring; progression from the dal e of the earlier of two consecutive CD4 counts less than or equal to 2 00 x 10(6)/l (termed as CD200) to AIDS. Setting: Scotland's HIV Immuno logy Laboratories and the Scottish Centre for Infection and Environmen tal Health. Patients: A total of 1679 adult HIV patients in Scotland t o 31 December 1994 who had ever had a CD4 cell count less than or equa l to 500 x 10(6)/l or who had developed AIDS without any immunological monitoring, of whom 912 had developed severe HIV-related immunodefici ency (i.e., were CD200/AIDS cases). Results: Square-root first CD4 cou nt was higher in women (by 2.1; SE, 0.5), in injecting drug users (IDU ; by 1.8; SE, 0.5) and in younger patients (by 1.5 per 10 years; SE, 0 .2), but reduced by 1.5 (SE, 0.1) per calendar year of recruitment, al though it was relatively higher (by 3.8; SE, 0.8) for Edinburgh patien ts recruited in 1993-1994: at least 30% (nine out of 28) of new Edinbu rgh City Hospital patients in 1993-1994 with a first CD4 count of grea ter than or equal to 500 x 10(6)/l had seroconverted within the past 5 years. Two-thirds of non-IDU (67%; 348 out of 517) were already sever ely immunodeficient at or before the start of immunological monitoring , in contrast with only 31% of IDU CD200/AIDS cases. Overall, the odds on the CD200 date also being the date of first CD4 count have increas ed in recent times [log(e)(odds per calendar year of CD200 diagnosis), 0.14; SE, 0.05]. Analysis excluding patients whose AIDS diagnosis or follow-up time was within 1 month of the CD200/AIDS date supported a m odest prolongation of the CD200/AIDS to AIDS interval for patients dia gnosed with severe HIV-related immunodeficiency in the period 1989-199 1 (log(e)[relative risk (RR)]; -0.46; SE, 0.22). Similarly, year effec ts were evident on progression from CD500 to CD200/AIDS [log(e)(RR), - 0.55; SE, 0.17) for CD500 cases diagnosed in 1989, and these year effe cts doubled in 1990-1992. Conclusions: Minimal CD4 data were hypothesi s-generating about region, risk group and calendar year. Lower bound f or recent HIV incidence can be derived from new patients with first CD 4 cell count above 500 x10(6)/l if seroconversion intervals are availa ble for a proportion.