What is legionella?

Legionella is a genus of pathogenic bacteria that causes Legionnaires’ disease (legionellosis)–as well as Pontiac fever–which affects 8,000 to 18,000 people a year in the United States. The name comes from an outbreak of pneumonia–due to the bacteria–after an American Legion convention in 1976.

Pontiac fever is a lesser form of legionellosis. Its symptoms usually last for two to five days and the person doesn’t get pneumonia. It is also caused by the legionella bacteria.

Where does legionella come from?

Legionella are naturally occurring and survive in a wide range of environmental conditions. They live in soil, lakes, creeks, and even aquifers. They survive by consuming the remains of dead bacteria that they come in contact with, which makes older water systems ideal for legionella growth as there is an ample supply of biomass (a.k.a. “bacteria food”).

The legionella bacteria spread around a water system by first attaching to microorganism communities contained in biofilms. A biofilm is a vast array of microorganisms that stick together by excreting a glue-like sludge made of sugars. These communities grow in size as other microorganisms attach to it, which supplies legionella with plenty of food to continue multiplying. Once the community reaches a sufficient size it can’t hold onto its original mounting point and sloughs off down the waterway, breaking up and spreading the legionella bacteria throughout the water supply.

How do you get Legionnaire’s disease, or Pontiac Fever, from legionella?

Legionella are dangerous when inhaled, which can lead to severe pneumonia (legionellosis) after about 2-14 days. The bacteria get into the lungs via tiny water droplets, like those created by showerheads, drinking fountains, or air conditioners. Hot tubs in particular are ideal for bacterial growth like legionella.

Most large-scale outbreaks of legionella involve water cooling towers that are part of older buildings, such as hotels, schools, and hospitals. These units were later shown to have been building up biofilms in their water lines for some time and were built without antibacterial measures put in place.