Legionellosis (Legionnaires' Disease)

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 breathing in small droplets of water in the air that are 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 cough. Other symptoms may include a high fever, chills, myalgia, muscle aches, and/or headache. Abdominal pain, nausea, vomiting, and diarrhea are also common, and some people may have confusion or other mental changes.  
  
• Pontiac Fever presents as a self-limited febrile illness that does not result in pneumonia. Symptoms may include fever, headache, malaise, and muscle aches.

Prevention
The key to preventing legionellosis is maintenance of the water systems in which Legionella grow, including drinking water systems, hot tubs, decorative fountains, misters, 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 122°F 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 2004 to 2016, the number of legionellosis cases reported to DSHS ranged from a low of 69 cases (0.3 cases per 100,000 population) in the year 2006 to a high of 292 cases (1.1 cases per 100,000 population) in 2015.  

In Texas, the highest age-specific rates of legionellosis are typically found among middle aged and older adults. In 2016, 150 cases (3.1 cases per 100,000 population) were 60 years and older, 67 cases (1.9 cases per 100,000 population) were 50-59 years of age, 27 cases (0.7 cases per 100,000 population) were to 40-49 years of age. Although legionellosis cases are rarely reported in children in Texas, one case of legionellosis was reported in 2014 in a neonate following a water birth (Fritschel E, Sanyal K, Threadgill H, Cervantes D. Fatal legionellosis after water birth, Texas, USA, 2014. Emerg Infect Dis [Internet]. 2015 Jan [2015 Jul]. http://dx.doi.org/10.3201/eid2101.140846).