CDC scientists discovered Legionnaires’ disease in 1976, during one of the largest respiratory disease investigations in U.S. history. CDC’s disease detectives were called upon when people became sick with pneumonia, a serious lung infection, while attending an American Legion convention at a hotel in Philadelphia. Findings from the investigation suggested that a germ was being spread by the hotel’s air conditioning system.  Six months later, CDC scientists identified that germ.  It was a previously unknown bacteria, which they named Legionella.

Legionnaires’ disease is on the rise

Legionnaires’ disease is caused by breathing in small water droplets that are contaminated with Legionella germs. In 2015, about 5,000 people were diagnosed with Legionnaires’ disease and in recent years there have been at least 20 reported outbreaks. Most people who get sick need hospital care and make a full recovery; however, about 1 in 10 people will die from the infection.

Between 2000 and 2014, the number of people with Legionnaires’ disease grew by nearly four times. This increase is likely due to a number of factors, including:

• A greater number of people who are at risk for Legionnaires’ disease because of an underlying illness or medications that weaken the immune system
• An aging U.S. population, with adults over the age of 50 being at a higher risk of getting the disease
• An outdated plumbing infrastructure, which allows for Legionella to grow in the pipes

Outbreaks of Legionnaires’ disease are preventable

CDC investigations of Legionnaires’ disease outbreaks show that the most common places for getting the disease are hotels, long-term care facilities, and hospitals.  The most likely sources for spreading water droplets contaminated with Legionella germs are showers and faucets, cooling towers that are part of large, centralized air conditioning systems, hot tubs, and decorative fountains and water features.

Four different types of problems have been associated with Legionnaires’ disease outbreaks. In nearly half of these outbreaks, more than one of these problems was identified.

• Process failures, such as not having a Legionella water management program
• Human errors, such as a hot tub filter not being cleaned or replaced as recommended by the manufacturer
• Equipment breakdowns, such as a disinfection system that was not working
• Changes in water quality that were due to reasons external to the building itself, such as nearby construction

Building owners and managers need to take steps to reduce the risk of Legionnaires’ disease through effective water management. It is important for everyone to work together to lower this risk by reducing the growth of Legionella in buildings and limiting places where people can be exposed.

This July marks the 40^th anniversary of the convention of the American Legion in Philadelphia.  This anniversary serves as a reminder that implementing effective water management programs in buildings could go a long way toward reducing the risk of Legionnaires’ disease.

Learn more about Legionnaires’ disease in this month’s issue of Vital Signs: www.cdc.gov/vitalsigns/legionnaires