title: Identifying recent HIV infections using the avidity index and an automated enzyme immunoassay.
abstract: We evaluated a procedure for identifying recent HIV infections, using sequential serum samples from 47 HIV-positive persons for whom the seroconversion date could be accurately estimated. Each serum sample was divided into two aliquots: one diluted with phosphate-buffered saline and the other diluted with 1 M guanidine. We assayed the aliquots with the automated AxSYM HIV1/2gO test (Abbott Diagnostics Division), without modifying the manufacturer's protocol. We then calculated the avidity index (AI): the ratio of the sample/cutoff value for the guanidine aliquot to that of the phosphate-buffered saline aliquot. We analyzed 216 serum samples: 34 samples were collected within 6 months of seroconversion (recent seroconversions), and 182 were collected after 6 months. The mean AIs, by time from seroconversion, were 0.68 +/- 0.16 (within 6 months) and 0.98 +/- 0.10 (after 6 months) (P < 0.0001). AI of <0.90 correctly identified 88.2% of recent infections but misclassified as recent infections 13.2% of serum samples collected afterward. The probability of an infection being classified as recent and having AI of > or = 0.90 would be 0.7% in a population with 5% recent infections. AI can identify with a certain degree of accuracy recent HIV infections, and being a quantitative index, it provides different levels of sensitivity and specificity, depending on the selected cutoff value. The standard assay procedure is not modified. This test is simple and inexpensive and could be used for surveillance, decision-making in treatment, and prevention.
authors.affiliation: Reparto AIDS e MSTl, Istituto Superiore di Sanità, Rome, Italy. suligoi@iss.it
authors.forename: Barbara
authors.initials: B
authors.lastname: Suligoi
authors.forename: Mario
authors.initials: M
authors.lastname: Massi
authors.forename: Claudio
authors.initials: C
authors.lastname: Galli
authors.forename: Mauro
authors.initials: M
authors.lastname: Sciandra
authors.forename: Fiorella
authors.initials: F
authors.lastname: Di Sora
authors.forename: Patrizio
authors.initials: P
authors.lastname: Pezzotti
authors.forename: Olga
authors.initials: O
authors.lastname: Recchia
authors.forename: Francesco
authors.initials: F
authors.lastname: Montella
authors.forename: Alessandro
authors.initials: A
authors.lastname: Sinicco
authors.forename: Giovanni
authors.initials: G
authors.lastname: Rezza
mesh_terms: D000293:Adolescent; D000328:Adult; D000915:Antibody Affinity; D001331:Automation / Q000379:methods; D005260:Female; D015658:HIV Infections / Q000175:diagnosis*; D006801:Humans; D007124:Immunoenzyme Techniques / Q000379:methods*; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012680:Sensitivity and Specificity