The bacterium Legionella pneumophila is a dangerous indoor air quality contaminant that’s worth a second look, because many of us assume it’s an issue at conventions and in large buildings but not at home.

Wrong.

In fact, one in five cases of potentially deadlyLegionnaires’ diseaseis contracted by inhaling the bacterium at home. Research shows that the bacteria grow quite well in slime that lines residential hot water pipes and HVAC systems.

Earlier this year, Los Angeles County health officials found Legionnella bacteria at the Playboy Mansion in Los Angeles after 200 people became sick following a fundraising event. Those attending the event fell ill with Pontiac fever, a milder form of the disease which causes flu-like symptoms.

The bacteria are spread when people inhale small droplets of water suspended in the air containing the contaminant. It can also spread when a person drinking water coughs or chokes while drinking, inadvertently inhaling the deadly bacteria.

The bacteria flourish in temperatures between 90 and 105 degrees Fahrenheit. Often, homeowners set their hot water tanks on low temperatures to prevent scalding and to save energy. But experts recommend turning the temperature of your tank up to 140 degrees and running hot water for half an hour to purge your home water system.

There are lifestyle and other factors that can contribute to your risk of developing a Legionnaires’ infection, including:

• Smoking
• Weakened immune system
• Chronic lung disease
• Age 65 or older
• Job requires maintaining cooling towers in air conditioning systems

Legionnaires’ disease takes it name from the outbreak at a Philadelphia hotel convention of the Pennsylvania American Legion in 1976. Thirty-five people dies in the outbreak.