Rising incidence of Legionnaires’ disease due to cleaner air

A study links a rise in a serious bacterial illness to an unexpected factor: a decline in air pollution. Legionnaires’ disease is a respiratory illness with a fatality rate of 10–25% that is caused by inhaled Legionella bacteria. The bacteria live in water and outbreaks have been linked to water sources such as cooling towers, which cool indoor spaces by dissipating heat into the atmosphere in the form of water droplets and vapor. Other sources include improperly maintained public fountains, hot tubs, ice machines, home humidifiers, and showers. A global rise in Legionnaires’ disease since the year 2000 has puzzled experts. In the United States, reported cases of Legionnaires’ disease increased from 1,100 cases in 2000 to nearly 10,000 cases in 2018. Fangqun Yu, Arshad Arjunan Nair, and colleagues link the increase to a decline in sulfur dioxide (SO₂) air pollution. Airborne water droplets carrying Legionella bacteria uptake SO₂ from the ambient air, which can make the water droplet acidic and inhospitable for the bacteria when SO₂ levels are high. As SO₂ pollution declined nationally, the bacteria lived longer in airborne droplets, increasing the chances that viable bacteria could end up in a person’s lungs. According to the authors, reducing SO₂ pollution has many well-established health benefits and should not be discouraged, but public health officials and clinicians should be aware of the potentially increased risk for Legionnaires’ disease.