On the 13th, Seibu Lions announced on their official website that a spectator who attended their game against Softbank Hawks Hawks at Belluna Dome on the 5th had tested positive for measles. They issued a warning to fans.

The website stated, "We would like to inform you that a customer who attended Fukuoka Softbank Hawks game on May 5, 2026 (Tuesday, national holiday) has tested positive for measles as a result of a medical examination."

They continued, "To everyone who has come to Belluna Dome, if you experience any symptoms that suggest measles (fever, rash, cough, runny nose, conjunctivitis, etc.), please be sure to contact a medical institution in advance before seeking treatment. Also, please wear a mask when visiting a medical institution and refrain from using public transportation as much as possible."

The statement concluded by saying, "We will continue to strive for safety management under the guidance of administrative agencies so that everyone can enjoy watching baseball with peace of mind."

The usage time for Belluna Dome was listed as "13:00 to 17:10," and the facility used (where the game was watched) was listed as "The Lions outfield Reserved Seat B [Left Field]."