Cases of Legionnaires' disease, often mistaken for a summer cold or air-conditioning sickness due to symptoms such as dry cough, fever, and body aches, have risen sharply in Korea this year.
According to the Korea Disease Control and Prevention Agency's (KDCA) infectious disease portal, 247 cases of Legionnaires' disease were reported nationwide between January and April this year. The figure represents a 56.3% jump from 158 cases during the same period last year.
Legionnaires' disease is a respiratory infection caused by the Legionella bacterium and was designated as a Class 3 statutory infectious disease in 2000. Last year's annual case count of 599 was the highest since related statistics began being compiled in 2001. Given that cases typically concentrate in July and August when temperatures rise sharply, this year's total could surpass last year's record.
Legionella bacteria normally exist at low concentrations in rivers and streams but multiply rapidly in warm water environments. They thrive particularly in poorly managed facilities such as stagnant water at 25 to 45 degrees Celsius, cooling tower water, aging pipes, water supply systems, swimming pools, and fountains.
The concern is that the bacteria can spread through the air in droplet form and infect people through the respiratory tract. However, person-to-person transmission, as seen with COVID-19, is known to be rare.
Symptoms are broadly divided into a flu-like form and a pneumonia form. The flu-like form, known as Pontiac fever, initially presents with cold-like symptoms including fever, muscle pain, and cough, and most patients recover naturally within a week.
The pneumonia form is a different matter. It causes dry cough, high fever, chest pain, headache, and muscle pain, and in severe cases can lead to breathing difficulties. Those aged 50 and older, patients with chronic lung disease, people with weakened immune systems, and those with underlying conditions face a particularly high risk of progressing to severe illness.
Deaths from Legionnaires' disease have also continued. According to the KDCA, a total of 110 people died from the disease between 2020 and 2024. In both 2023 and 2024, 28 people died each year.
Health authorities cite climate change and aging facilities as the main reasons behind the recent rise in cases. Rising temperatures have pushed up water temperatures themselves, while inadequate management of water supply equipment at facilities whose use had declined after COVID-19 has created an environment conducive to bacterial growth, officials explained.
"Legionella bacteria multiply quickly enough to cause infection above a certain temperature," a KDCA official told Yonhap News. "The recent rise in patients appears to stem from higher water temperatures due to climate change, combined with the aging of equipment at large facilities."
The official added, "Regular inspection and monitoring are important for facilities requiring infection-source management, such as swimming pools and cooling towers. On a personal level, observing basic hygiene rules such as washing hands after going out is helpful."
