11% of Seoul public facilities test positive for Legionella, with bathhouses hit hardest

Legionella bacteria have been detected at bathhouses, jjimjilbang and other public facilities across Seoul, with a positive rate of 11 percent.

The Seoul Institute of Public Health and Environment said Saturday it had conducted Legionella testing at public facilities — including bathhouses and jjimjilbang, general hospitals, elderly welfare facilities and department stores — between April and August this year.

Of 2,214 samples analyzed from public facilities, 246, or 11.1 percent, tested positive for Legionella. By facility type, bathhouses and jjimjilbang recorded the highest number at 162 cases, followed by general hospitals with 34, care centers with 6, and hotels and inns with 4. No Legionella was detected at elderly welfare facilities.

For facilities where Legionella was found, the institute has directed building owners and managers to carry out immediate cleaning and disinfection, and is conducting follow-up tests until safety is confirmed.

Legionella thrives in warm, humid environments — specifically at temperatures between 25 and 45 degrees Celsius and a pH of 7.2 to 8.3. The bacteria live in contaminated water such as cooling tower water in large buildings like department stores and hospitals, bathhouse water and household plumbing, and infect people through the respiratory tract. Person-to-person transmission is not known to occur, but high-risk groups — including people with chronic lung disease, diabetes or hypertension, smokers and those with weakened immune systems — face a significantly greater risk of infection and should take precautions.

The number of Legionnaires' disease patients declined somewhat during the COVID-19 pandemic but has been rising again since 2023. As of Aug. 31 this year, the national total stood at 509 cases, of which 140, or 27.5 percent, were reported in Seoul.

Maintaining water temperatures outside the bacteria's ideal range is the most effective way to control Legionella. The institute advised that hot water should be kept at 50 degrees Celsius or above and cold water at 20 degrees Celsius or below, since the bacteria multiply most readily between 25 and 45 degrees Celsius.

"Regular cleaning and disinfection are essential to blocking Legionella," said Park Ju-seong, director of the institute. "We will continue retesting facilities where the bacteria were found until their safety is confirmed, so that citizens can feel at ease."