Legionella species are gram negative bacilli commonly found in water. There are over 50 species and ~70 serogroups currently recognized. L. pneumophila serogroup 1 is primarily responsible for human disease.
Transmission occurs by inhaling mist from a water source contaminated with the Legionella bacteria. An example is breathing in steam from a contaminated hot tub. Transmission may also occur by aspirating contaminated water. No human-to-human transmission occurs.
There are two distinct clinical manifestations of disease:
- Legionnaires’ Disease presents as pneumonia with a non-productive cough. Symptoms may include a high fever, chills, cough, muscle aches, and/or headache. Abdominal pain, nausea, vomiting, and diarrhea are also common.
- Pontiac Fever presents as a self-limited febrile illness that does not result in pneumonia. Symptoms may include fever, headache, and muscle aches.
The key to preventing legionellosis is maintenance of the water systems in which Legionella grow, including drinking water systems, hot tubs, decorative fountains, and cooling towers. Cooling towers should be drained when not in use and mechanically cleaned periodically to remove scale and sediment. Appropriate biocides should be used to limit the growth of Legionella and the formation of protective biofilms. Maintaining hot water system temperature at 50°C or higher may reduce the risk of transmission. Tap water should be not used in respiratory therapy devices.
There are no vaccines that can prevent legionellosis. Persons at increased risk of infection may choose to avoid high-risk exposures, such as being in or near a hot tub.
Recent Texas Trends
From 2003 to 2013, the number of legionellosis cases reported to DSHS ranges from a low of 69 cases (0.3 cases per 100,000 population) in the year 2006 to a high of 168 cases (0.6 cases per 100,000 population) in 2013.
In Texas, the highest age group-specific rate of legionellosis is found among adults 60 years and older. In 2013, 89 cases (2.2 cases per 100,000 population) were 60 years and older, 43 cases (1.3 cases per 100,000 population) were 50-59 years of age, 19 cases (0.5 cases per 100,000 population) were to 40-49 years of age, 13 cases (0.3 cases per 100,000 population) were 30-39 years of age, and 4 cases (0.1 cases per 100,000 population) were 20-29 years of age.