What is the best explanation from the nurse as to why a client must return to the unit in 48 hours after having a tuberculin skin test intradermal?

A tuberculin skin test  is done to see if the patient has ever been exposed to the bacteria that causes tuberculosis (Mycobacterium tuberculosis). The test is done by putting a small amount of antigens of the bacteria under the skin.
 If the patient was exposed, there will be a firm red bump where the antigens were placed but it would take 2 days to see the results so the patient needs to come back again after that time.

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When a virus infects a host cell, it uses the cell's machinery to make copies of its own genetic material in a process called replication. finally, during the process of self-assembly, that protein shell and the copies of the virus's genetic material are assembled into new viruses.