BACKGROUND: The routine HIV screening essentially depends on the detection of 
HIV specific antibodies. However, HIV p24 antigen can be detected in individuals 
with recent HIV infection about 2-18 days prior to seroconversion. New fourth 
generation HIV screening assays combine the detection of anti-HIV antibodies 
with the simultaneous detection of HIV p24 antigen. This may result in a 
reduction of the diagnostic window after primary infection.
OBJECTIVES: The performance of two novel fourth generation assays in routine 
diagnostic was evaluated.
STUDY DESIGN: We compared two third generation, two fourth generation and one 
antigen HIV assays in a case with acute primary HIV infection.
RESULTS: In our case, the HIV infection was detected 11 days earlier with the 
fourth generation assays compared to third generation assays. Interestingly, 
after the initial reactive results the fourth generation assays became negative 
resulting in a second diagnostic window. During this second diagnostic window 
neither third nor fourth generation HIV assays were reactive. This second 
diagnostic window was caused by the absence of HIV specific antibodies and the 
decline of HIV p24 antigen concentrations below the detection limits of the 
fourth generation assays.
CONCLUSIONS: Fourth generation assays markedly improve the diagnosis of recent 
HIV infections but the possibility of a second diagnostic window must be 
considered.