OSAKA - Legionella bacteria have been detected in multiple locations at the Osaka-Kansai Expo site, prompting health and safety measures. According to the Japan Association for the 2025 World Exposition, seawater collected on June 3rd from the Water Plaza, where water shows are held, was found to contain Legionella bacteria at 20 times the guideline limit.
The Osaka city government stated that when such levels are exceeded, inhaling aerosolized droplets containing the bacteria could significantly increase the risk of pneumonia. The city’s public health office instructed the Expo organizers to suspend fountain operations, leading to the cancellation of both daytime and evening water shows while the source of contamination is being investigated.
A visitor commented, "I’m disappointed because the only reservation I could get was for the water show."
The association also confirmed that on May 30th, elevated levels of Legionella had already been found at the same Water Plaza site, but the results were not disclosed at the time, and the show continued as planned. On the reason for this, Expo Deputy Secretary General Takashina explained, "The initial test was a simple check that only confirmed the presence of the bacteria, so there were no directives to suspend operations. We were told to wait for the detailed analysis, which would come later."
Additionally, on June 5th, the association revealed that Legionella bacteria above the guideline limit had also been detected on the south side of the "Quiet Forest" area in the center of the Expo grounds. The contamination was found on the night of May 28th, but was not publicly announced, and the site was quietly closed from the morning of May 30th.
At a press conference on June 5th, Koji Yamakita, acting director of the Facilities Maintenance Bureau of the Expo Association, stated, "There was no intention to delay the announcement. We only received the notice yesterday and are releasing the information today. There is currently no danger posed by the bacteria."
The association said it will carry out disinfection and other safety measures at both the Water Plaza and the waterside area of the Quiet Forest.
Legionella bacteria, known in Japanese as レジオネラ属菌, have a history in Japan that reflects the nation’s evolving public health challenges, particularly in relation to its widespread use of communal water facilities such as onsen (hot springs), sento (public baths), and hospital water systems. The bacterium was first globally recognized in 1976 following the deadly outbreak at an American Legion convention in Philadelphia, but it wasn't until 1987 that Japan reported its first major domestic case, involving an outbreak in a hospital in Gunma Prefecture. This incident drew attention to the potential for Legionella to thrive in artificial water systems, particularly those that generate aerosols, and raised alarms about Japan’s aging infrastructure and the unique risks posed by its bathing culture.
Through the 1990s, sporadic cases emerged in various parts of the country, with infections frequently linked to poorly maintained water systems in hotels, hospitals, and public facilities. As Japan’s population aged and more people became reliant on care facilities with complex water systems, the need for regular water sanitation and monitoring became increasingly apparent. However, the real turning point in public and governmental awareness came in 2002 when a large-scale outbreak occurred at a public bathhouse in Miyazaki Prefecture. This incident resulted in over 200 infections and at least seven deaths, making it one of the deadliest Legionella outbreaks in Japan. The bacteria had spread through improperly treated, recirculated bathwater, exposing systemic flaws in facility management and hygiene practices.
In response, the Japanese government began to introduce stricter regulatory measures, including revisions to the Public Bathhouse Law (公衆浴場法), which mandated regular water quality testing, improved disinfection procedures, and better documentation of cleaning routines. These rules were supported by detailed guidelines from the Ministry of Health, Labour and Welfare on how to control Legionella in high-risk facilities such as hospitals, nursing homes, hotels, and spa centers. Despite these efforts, cases continued to be reported throughout the 2010s, particularly in locations with older plumbing systems or inconsistent maintenance standards. Cooling towers and water fountains in urban commercial buildings also emerged as infection sources, revealing that even outside traditional bathhouse environments, the risk of airborne Legionella exposure remained significant.
In more recent years, Legionella-related incidents have continued to occur, with several affecting nursing homes and rehabilitation centers where vulnerable elderly residents were exposed. These cases underscored the importance of continuous monitoring and the dangers of even small lapses in water system hygiene.
Source: MBS
