A method for assessing viral, e.g., HIV, infection duration in a subject, which method comprises:
- a) contacting a sample from a subject with a system, which system comprises:
- A) a lateral flow test device comprising a porous matrix that comprises, from upstream to downstream,
- a sample application site configured to receive a sample liquid from a subject, and a first test location comprising an immobilized first binding reagent that specifically binds to an anti-viral antibody, e.g., anti-HIV antibody, in said sample liquid having a first average antibody avidity,
- wherein, relative to said anti-viral antibody, e.g., anti-HIV antibody, in said sample liquid, said first binding reagent is limiting and said anti-viral antibody is in excess, and said sample liquid flows laterally along said lateral flow test device and passes said first test location to form a first detectable signal comprising multiple signal pixels;
- and
- B) a reader configured to measure both the number of said signal pixels and the intensities of said signal pixels in said first detectable signal to generate a first quantitative signal readout that is used to assess average antibody avidity of said anti-viral antibody, e.g., anti-HIV antibody, in said sample liquid and/or viral, e.g., HIV, infection duration in said subject,
- wherein said liquid sample is applied to a site of said lateral flow test device upstream of said first test location;
- b) transporting an anti-viral antibody, e.g., an anti-HIV antibody, if present in said liquid sample, and a labeled reagent to said first test location to form a first detectable signal at said first test location, said first detectable signal comprising multiple signal pixels;
- and
- c) measuring both the number of said signal pixels and the intensities of said signal pixels in said first detectable signal using said reader to generate a first quantitative signal;
- and
- d) assessing average antibody avidity of said anti-viral antibody, e.g., anti-HIV antibody, in said sample liquid and/or viral, e.g., HIV, infection duration in said subject based on said first quantitative signal.