NASCAR champion Kyle Busch, 41, dies from pneumonia-linked sepsis

Kyle Busch, a two-time NASCAR Cup Series champion and the all-time leader in wins across the sport's top three national series, died Thursday at 41 after severe pneumonia progressed into life-threatening sepsis, according to his family.

Busch's 234 career victories across NASCAR's three national series were the most in the sport's history. His death from a respiratory illness that began as a sinus cold less than two weeks before he collapsed has drawn renewed attention to sepsis, which the Centers for Disease Control and Prevention describes as a life-threatening emergency triggered by the body's overwhelming response to infection.

Busch had developed a sinus cold while competing at Watkins Glen on May 10, according to ABC7 Los Angeles. The illness worsened over the following 11 days, and on the afternoon of Wednesday, May 21, he became unresponsive while testing in a Chevrolet racing simulator at a facility in Concord, N.C.

During the emergency call placed that afternoon, an unidentified caller calmly told dispatch: "I've got an individual that's (got) shortness of breath, very hot, thinks he's going to pass out, and is producing a little bit of blood, coughing up some blood," according to audio from the Cabarrus County Sheriff's Office.

Emergency responders transported Busch to a Charlotte-area hospital, where he died the following day, Thursday, May 22. His family said a medical evaluation confirmed that severe pneumonia had progressed to sepsis — a life-threatening condition in which the immune system's extreme response to infection causes widespread inflammation, blood clots and organ damage, according to the CDC.

Busch won two NASCAR Cup Series championships and accumulated 234 victories across NASCAR's top three national series — more than any other driver in the history of the sport, ABC7 Los Angeles reported.

All 39 drivers in the field for Sunday's race honored Busch by racing with a black No. 8 decal on their cars, the Associated Press reported.

His 234 wins across NASCAR's three national series — a record no other driver had ever reached — stand as the defining legacy of a career cut short at 41.