A clinician wants to know if a patient is actively shedding a respiratory virus right now. Which FA format is appropriate and why?

Use a direct FA test because fluorescently labeled primary antibodies will bind viral antigen present in the patient sample and indicate current infection.

Use an indirect FA test because fluorescent secondary antibodies bind host complement on the slide and provide a sensitive readout of viral shedding over weeks after infection.

Use a serological ELISA that detects IgG with fluorescent tertiary antibodies because IgG levels rise immediately at the onset of infection and are the best marker for current viral shedding.

Use Western blotting instead because it uses gel separation which is the only method capable of distinguishing active viral replication from past exposure reliably in a single step.