23 October 2013
Compared with Europeans who had a current CD4 count between 750 and 999 cells/µL, those with 500 to 749 cells/µL had a 20% higher incidence of AIDS-defining illness. The risk in the 500-749 CD4 group was even higher for AIDS-defining malignancies.
As people respond to combination antiretroviral therapy, their CD4 counts usually climb above 500 cells/µL and even higher. Because the risk of new AIDS diagnoses at such high CD4 counts remains poorly understood, researchers analyzed people at least 14 years old who had at least one CD4 count above 200 cells/µL between 1998 and 2010 in the Collaboration of Observational HIV Epidemiological Research Europe (COHERE) cohort.
The COHERE team calculated incidence of each AIDS-defining illness in different CD4 strata and used Poisson regression analysis to model rates of new AIDS diagnoses at current CD4 counts of 500 cells/µL or higher.
During the study period, 12,135 new AIDS illnesses developed at a CD4 count at or above 200 cells/µL in 207,539 people with 1,154,803 person-years of follow-up. Incidence of AIDS illness dropped from 20.5 per 1000 person-years with a current CD4 count of 200 to 349 cells/µL to 4.1 per 1000 with a current CD4 count at or above 1000 cells/µL.
People with a current CD4 count between 500 and 749 cells/µL had a 20% higher incidence of AIDS illness than people with a current CD4 count between 750 and 999 cells/µL (adjusted incidence rate ratio [aIRR] 1.20, 95% confidence interval 1.10 to 1.32). But AIDS incidence did not differ significantly between people with a current CD4 count at or above 1000 cells/µL and those with a count between 750 and 999 cells/µL (aIRR 0.92, 95% CI 0.79 to 1.07). These findings were consistent with high or low viral loads.
Incidence of AIDS-defining malignancies was 52% higher with 500 to 749 cells/µL than with 750 to 999 cells/µL (aIRR 1.52, 95% CI 1.25 to 1.86), whereas incidence of nonmalignant AIDS diagnoses was 12% higher in the 500-749 CD4 bracket (aIRR 1.12, 95% CI 1.01 to 1.25).
The COHERE team believes their findings suggest that “immune reconstitution is not complete until the CD4 increases above 750 cells/µL.”
Because the higher AIDS risk with 500 to 759 cells/µL held true regardless of viral load, the researchers suggest that “immune-mediated mechanisms other than those induced by HIV replication alone are responsible for this increased rate.”
Source: A. Mocroft, H.J. Furrer, J.M. Miro, et al. The incidence of AIDS-defining illnesses at a current CD4 count ≥200 cells/µL in the post–combination antiretroviral therapy era. Clinical Infectious Diseases. Published online 6 August 2013.
Complete article available at www.natap.org.
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