Southwest Airlines issued this statement:

“Although testing negative multiple times prior to the Senate Commerce Committee Hearing, Gary Kelly tested positive for COVID-19 after returning home, experiencing mild symptoms, and taking a PCR test.”

More from CNBC:

https://www.cnbc.com/2021/12/17/southwest-ceo-tests-positive-for-covid-after-unmasked-senate-hearing-with-other-airline-chiefs.html