The largest cohort study ever to look at CD4 count and viral loads in HIV-positive people around the time of diagnosis has found evidence that HIV, at least in Europe, has become more virulent over time. The average time taken to reach a CD4 count below 350 cells/mm³ has halved over the last 25 years, researchers calculate.

The study of 15,875 patients within the pan-European CASCADE cohort finds that the estimated CD4 count after seroconversion (a measure of how strongly the acute phase of HIV infection attacks the immune system) fell from 770 cells/mm³ in 1979 to 570 cells/mm³in 2002.