Definitions of dates and time intervals relative to BED testing.

<p>The time since seroconversion (<i>t</i>) is the time from the date a patient seroconverted (<i>T</i>_sc) to when a sample for BED testing was collected (<i>T</i>_BED). We estimate <i>t</i> by a logistic IgG model (Eq. 1) as ^∧<i>t</i>. Date of infection (<i>T</i>_inf) occurred on average 21 days prior to <i>T</i>_sc<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0060906#pone.0060906-Fiebig1" target="_blank">[9]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0060906#pone.0060906-Cohen1" target="_blank">[10]</a>. When available, the patient history also includes the dates of last negative HIV-1 antibody testing (<i>T</i>₍₋₎) and first positive HIV-1 antibody testing (<i>T</i>₍₊₎), defining the serological interval. Note that <i>T₍₊₎</i> and <i>T_BED</i> may often occur at the same date. To reevaluate national Swedish HIV surveillance data we compared ^∧<i>T</i>_inf with <i>T</i>₍₊₎, resulting in a time difference Δ.