An outbreak of Legionnaires’ disease in New York City this August has sickened more than 100 people and left five dead. Throughout the U.S. reported cases of this severe form of pneumonia have risen significantly over the last 25 years, with most occurring in summer and autumn.
The disease is caused by any species of Legionella bacteria (such as L. pneumophilia). These are aerobic, pleomorphic, flagellated, non-spore-forming, Gram-negative bacteria. The organisms can thrive in water systems, capable of surviving diverse range of environmental conditions, tolerating temperatures from 0°C-63 °C, a pH range of 5.0-8.5, and in dissolved oxygen concentrations of 0.2-15.0 mg/litre.
Virginia Tech experts Amy Pruden and Kirin Furst have explained what the disease is, why it thrives in hot weather, and how to protect yourself.
How do people contract Legionnaires’ disease?
“People can contract Legionnaires’ disease if they inhale tiny droplets of water containing the bacteria Legionella, which can grow in the biofilms of pipes and fixtures that deliver drinking water to taps and shower heads, especially hot water lines,” Pruden said. “Legionella also can grow in water cooling towers, such as those that serve HVAC systems in large buildings.”
Why do rates of the disease rise during hot weather?
“In hot water heaters, the temperature often is not high enough to kill opportunistic pathogens like Legionella, which thrive in warm temperatures,” said Furst. “During the summer, water in the distribution pipes that bring water to your house can also heat up to optimal temperatures for Legionella, while causing the protective disinfectants like chlorine to decay a lot faster. Together, these conditions create a significant public health concern.”
How can cities control outbreaks?
“The New York City outbreak is a reminder that Legionella is the leading cause of waterborne disease and death in the U.S. We must remain vigilant in keeping it at bay in both cooling towers and drinking water systems to protect vulnerable populations,” said Pruden. “Building water system managers, especially at hospitals, nursing homes, apartment buildings, and hotels, should regularly test water temperature and disinfectant levels.”
How can people make sure their water is clean?
“If your ‘cold’ tap water runs very warm in the summer, I suggest getting a filter pitcher that you can keep in the fridge, so at least you have cold, clean drinking water,” said Furst. “But this won’t address exposure to Legionella or other pathogens that are primarily contracted while showering. For that, you could consider a whole-home water treatment system or a filter for your shower head. Just make sure any water treatment systems have been tested and certified by NSF for the contaminants you are concerned about.
Also, check your household plumbing configuration, as your pipes may run through an uninsulated part of your home, which will contribute to warming. If the water is already warm before it reaches your property because of heating in the distribution system, you could advocate for your municipality to increase shade coverage. Shade decreases both surface and subsurface temperatures, and may help keep water in distribution pipes and storage tanks cool in addition to many other benefits of shade.”
Pruden further explained that if you are in a risk group, like being elderly or immunocompromised, you might consider taking baths instead of showers.
“By doing this, you are less likely to inhale aerosols that contain the bacteria,” she said. “It’s also important to make sure your water heater is set above 140 F*, which is hot enough to kill the bacteria, but take care to mix with cool water in the tub to avoid scalding.”
*60 degrees Celsius, as the conventional expression of temperature
