The "lady who had diarrhea on Delta" refers to a viral and highly disruptive biohazard incident that occurred in September 2023 on Delta Flight DL194 from Atlanta to Barcelona. While the specific identity of the passenger was never officially released to the public out of medical privacy, the event became a global news sensation due to the graphic nature of the situation. Roughly two hours into the flight over Virginia, the pilot made an emergency U-turn, telling air traffic control, "It’s just a biohazard issue... we had a passenger who had diarrhea all the way through the airplane." Social media posts from other passengers described a "trail" of waste down the center aisle of the Airbus A350. The plane returned to Atlanta, where maintenance crews spent five hours deep-cleaning the cabin and completely replacing a section of the aisle carpet. The flight eventually took off again eight hours later with the same passengers (minus the ill individual). In the years since, the story has remained a staple of "travel horror stories," often cited as a prime example of why airlines take "onboard medical emergencies" involving infectious or biohazardous materials so seriously for the safety of the crew and other travelers.