Multi-country study on the impact of a revised consensus definition of late HIV diagnosis, Europe, 2022 to 2023.

BACKGROUNDWith improvements in test sensitivity and testing frequency, more people in Europe are diagnosed during the HIV acute/seroconversion phase, when their CD4+ T-cell count can be temporarily low.AIMWe piloted a revised definition of late HIV diagnosis for surveillance which considers laboratory markers, evidence of HIV test negativity in the past year and clinical evidence of recent HIV acquisition, to better distinguish between people diagnosed late and those diagnosed during the acute/seroconversion phase.METHODSWe collected pseudonymised HIV diagnosis records for 2022 and 2023 from nine European countries (Belgium, Czechia, Denmark, Germany, Greece, Italy, the Netherlands, Portugal and Sweden). We applied the revised definition to reclassify those with evidence of recently acquired HIV as 'not late' and calculated the corresponding correction factor by country and demographic group. Individuals with a previous diagnosis were excluded from the analysis.RESULTSAmong 10,220 individuals with a CD4+ T-cell count at diagnosis, 56% (5,689/10,220) had a CD4+ T-cell count < 350 cells/µL or an AIDS-defining event at diagnosis. Applying the revised definition reduced the late diagnosis proportion from 56% to 50%, a correction factor of 9% (535/5,689). The correction factor ranged between 3% and 25% across countries and was higher for younger ages and for gay, bisexual and other men who have sex with men, compared with other groups.CONCLUSIONSWithout reclassification, late HIV diagnosis proportions are overestimated. We provide recommendations and validity considerations for countries intending to use the revised definition.