How does an ELISA indirectly detect infection by a disease causing agent?

An ELISA (Enzyme-Linked Immunosorbent Assay) indirectly detects infection by measuring the presence of specific antibodies in a patient's serum that are produced in response to a disease-causing agent, such as a virus or bacteria. When the body is infected, it generates antibodies against the pathogen, which can be captured by antigens coated on a microplate. The amount of bound antibodies is then quantified using an enzyme-linked secondary antibody and a substrate that produces a measurable signal, indicating past or current infection. This method allows for the indirect assessment of infection by detecting the immune response rather than the pathogen itself.