Using 4th Generation HIV Testing to Diagnose Acute HIV Infections and Linking Patients to Care

Background: The 4^th generation HIV assay looks for both antibody and p24 antigen which allows detection of HIV infections earlier than previous test methodologies. Acute infection is defined as the time from HIV acquisition until seroconversion, when antibodies have formed. Subjects with acute HIV are extremely contagious immediately after acquiring infection and transmission is very likely. Early diagnosis represents a tremendous opportunity for treatment and prevention interventions.

Methods: In November 2012, the Illinois Department of Public Health (IDPH) laboratory began a new algorithm using the 4^th generation Abbot ARCHETECT Chemiluminescence Microparticle Immuno Assay (CMIA) as the screening test. All 4^th generation reactive tests are followed by the HIV type 1 and HIV type 2 differential test. All differential non-reactive tests reflex to Real-Time Reverse Transcriptase Polymerase Chain Reaction (PCR) testing. Any results CMIA reactive, differential non-reactive, PCR reactive are considered acute HIV cases because this testing pattern indicates detection of antigen not antibody.

Results: Between November 1, 2012 and August 31, 2013 IDPH laboratories performed 26,621 CMIA tests. 395 (1.5%) were CMIA reactive specimens. From these 10 (0.04%) were differential non-reactive, PCR reactive. Of these 10 acute cases, 8 of the 10 (80%) were linked to primary care.

Conclusions: The 4^th generation assay provides improved HIV diagnostic capabilities. The 10 acute cases would have appeared as negative with our previous 3^rd generation testing. Detecting HIV infections sooner will allow for medical care to begin at an earlier stage. Being able to detect new HIV infections earlier may also play a significant role in reducing community viral load and prevent further HIV transmissions.