A New Case Definition for HIV Infection

The surveillance case definitions for HIV infection and AIDS have been a work in progress for the last 30 years, as revisions keep pace with scientific advances. The newest revision combines case definitions for infants, children, and adults into a single document, incorporates new HIV-testing strategies, and aims to eliminate some of the ambiguity of past iterations. Two changes are most relevant to clinical practitioners:

1. The laboratory criteria for confirming HIV infection have been expanded to incorporate the newer testing algorithms that diverge from the usual enzyme-linked immunosorbent assay/Western blot sequence. For all adults, all children aged ≥18 months, and all younger children not at risk for perinatal infection, confirmed infection requires two positive immunologic tests that are “orthogonal,” using different antigens or principles. Acceptable combinations include an antigen/antibody test followed by an antibody-only test, an antibody test followed by a viral load assay, and a rapid antibody test followed by a conventional immunoassay (a positive Western blot is no longer required for diagnosis). A single positive result from a nonantibody test (p24 antigen, viral culture, viral load, or genotype) is also diagnostic.

2. The staging of HIV infection has been augmented by the addition of “stage 0” to indicate a very early infection diagnosed when standard markers are converting from negative to positive. The formal criteria specify a negative or indeterminate antibody, antigen/antibody, or nucleic acid test occurring within 6 months before a positive test of any type, or a positive test for HIV-specific viral markers occurring within 6 months of a negative or indeterminate antibody test. Criteria for stage 0 supersede and are independent of the criteria for other stages (which rely, as before, on CD4-cell counts and diagnosis of opportunistic illness). This new stage is particularly intended for patients with transiently low CD4-cell counts right after infection who in the past might have mistakenly been staged with advanced disease.

Other changes spell out up-to-date criteria for assigning “infected,” “uninfected,” and “indeterminate” status to children aged <18 months with perinatal HIV exposure and criteria for defining HIV-2 infection.