I was wondering if USA should contain periods and found this answer:

Use periods with the two-letter abbreviation for United States. Do not use periods with the three-letter abbreviation for United States of America. Use the abbreviation U.S. only as an adjective. Spell out United States when it is a noun.

• The U.S. government is one of the nation’s largest employers.
• Most of their products were made in the USA.

From the University of Colorado at Boulder Style Guide