In 2014, CDC updated its recommendations for HIV testing to improve the accuracy of laboratory diagnosis of HIV infection based on testing of serum or plasma specimens.24 Laboratory criteria for defining a confirmed case now accommodate new multi-test algorithms, including criteria for differentiating between HIV-1 and HIV-2 infection and for recognizing early HIV infection (Figure 1). To adapt to these changes, CDC also revised the surveillance case definitions for HIV infection.9
A confirmed case of HIV infection is now classified in one of five stages (0, 1, 2, 3, or unknown).9 Early infection, i.e., a negative HIV test within 6 months of HIV diagnosis, is classified as stage 0. If the criteria for stage 0 are not met, the stage is classified as 1, 2, 3, or unknown depending on CD4+ T-lymphocyte test results or whether an opportunistic illness was diagnosed >180 days after the diagnosis of HIV infection (Table 3). Acquired immunodeficiency syndrome (AIDS) is classified as stage 3.
|Stage 0||No opportunistic illnesses||If >180 days have elapsed after stage 0 at diagnosis, the stage at the later date is classified as 1, 2, 3, or unknown|
|Stage 1||No opportunistic illnesses||Either CD4+ T-lymphocyte count of ≥500 cells/μL or CD4+ T-lymphocyte percentage of total lymphocytes ≥26|
|Stage 2||No opportunistic illnesses||Either CD4+ T-lymphocyte count of 200-499 cells/μL or CD4+ T-lymphocyte percentage of total lymphocytes of 14-25|
|Stage 3 (AIDS)||At least one opportunistic illness||Either CD4+ T-lymphocyte count of <200 cells/μL or CD4+ T-lymphocyte percentage of total lymphocytes of <14.*|
|Stage unknown||No information on opportunistic illnesses||No information on CD4+ T-lymphocyte count or percentage.|