What do rapid assays for influenza detect in specimens obtained from nasopharyngeal swabs?

Rapid assays for influenza are specifically designed to detect the presence of influenza antigen in specimens obtained from nasopharyngeal swabs. These tests are based on the principle of immunochromatography, which identifies viral proteins (antigens) that are produced during an active influenza infection.

The detection of influenza antigen is crucial for swift diagnosis, allowing for timely treatment and public health measures. Unlike antibody-based tests, which would require time for the body to produce an immune response post-infection, antigen detection provides results that can indicate current infection almost immediately after symptom onset.

In this context, the other response options focus on various types of antibodies (IgM and IgA) or immune complexes, which are not the primary targets of rapid assays used for diagnosing influenza through nasopharyngeal samples. These tests function best when the virus is actively present in respiratory secretions, making antigen detection the most appropriate and effective method in this scenario.