Legionellosis (Legionnaires' 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.

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 not be 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.

From 2010 to 2019, the number of legionellosis cases reported to DSHS gradually increased from a low of 111 cases in 2011 to a high of 421 cases in 2019, followed by a drop to 316 cases in 2020.  

In Texas, the highest age-specific rates of legionellosis are typically found among middle aged and older adults. Although legionellosis cases are rarely reported in children in Texas, two cases of legionellosis were reported in 2019.

• Legionellosis Investigation Report Form (PDF) January 2018
• Investigation Guidance (PDF, 1057 KB)

Report Legionellosis (Legionnaires' Disease and Pontiac Fever) within 1 week (800) 705-8868. 

Reports from healthcare providers and laboratories may be submitted using the EPI-2 Initial Provider Disease Report Form. Health Departments may use the Legionellosis Investigation Report Form.

There is no vaccine for legionellosis.

Investigation Forms and Guidance Documents

• Legionellosis Investigation Report Form
• Investigation Guidance

Water Birth Infection Prevention Guidance and FAQ

• Legionella and Water Birth FAQ
• Texas Midwifery Water Birth Infection Prevention Guidance

Suggested Interview Questions for Legionella Remediation and Consulting Services

• Consulting Questions document

List of ELITE-certified laboratories

CDC’s Water System Maintenance website

Guidelines that can be found here include:

• American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (ASHRAE) Guideline 12-2000: Minimizing the risk of legionellosis associated with building water systems 2000
• ANSI/ASHRAE Standard 188-2015: Legionellosis: Risk Management for Building Water Systems
• Working with Legionella Consultants
• Guidelines for operating public hot tubs and whirlpool spas 

CDC’s Developing a Water Management Program Toolkit

Centers for Medicare and Medicaid Services Legionella Memorandum

• CMS Memo document

Report of the Texas Legionnaires’ Disease Task Force

In December 1999 a multidisciplinary task force was assembled to develop a Texas Legionnaires’ disease control plan to help local health officials respond to reports of legionellosis in hospitals, long-term care facilities, and the community. The task force was composed of state and local public health officials (epidemiologists, environmental) and university and hospital representatives (physicians, infection control practitioners, facility engineer). The written product of the task force, Report of the Texas Legionnaires’ Disease Task Force, was finalized in 2002. As of 2014, several portions of the Task Force document are outdated and conflict with current DSHS guidance on legionellosis outbreak investigation. Current outbreak investigation guidelines for legionellosis are available.

Legionellosis a generic term describing the pneumonic (Legionnaires’ disease) and non-pneumonic (Pontiac fever) forms of an acute, respiratory infection caused by the bacterium Legionella. An outbreak of this disease in Philadelphia in 1976, largely among people attending a state convention of the American Legion, led to its name.

Symptoms commonly include shortness of breath, headaches, fatigue, body aches, and fever. Non-productive cough, abdominal pains, and diarrhea occur in many patients. In patients with Legionnaires’ Disease, pneumonia develops which can cause death. With Pontiac fever there is no pneumonia, but the patient may have a high fever for 2-5 days and then recover without treatment. Legionellosis commonly occurs in patients who are elderly, immunocompromised, or otherwise in poor health.

Studies have shown that about 5% to 30% of known cases of Legionnaires’ disease have been fatal. However, many people may be infected with the bacterium causing Legionellosis without developing any symptoms. Others may be treated without having to be hospitalized. Recent information suggests that many cases of Legionellosis go undiagnosed. No deaths are associated with Pontiac fever.

Your physician can order tests to confirm the diagnosis of Legionellosis. The most useful tests include culturing the bacteria from sputum, detecting the presence of bacteria in a urine sample, and comparing antibody levels in two blood samples collected three to six weeks apart.

The currently recommended drug of choice is erythromycin, which appears to be effective in treating the disease. Other drugs are available for patients unable to tolerate erythromycin.

There is no evidence for person-to-person spread of the disease. Most people get the disease by inhaling small water droplets contaminated with Legionella bacteria. In some cases, the disease may be transmitted by aspirating contaminated water. Hot water distribution systems are commonly contaminated with Legionella. Common sources of legionella that can spread the bacteria include: hot tubs, showers, misters, decorative fountains, and cooling towers.

People of any age may get Legionellosis, but the illness most often affects middle-aged and older people, particularly those who smoke cigarettes or who drink heavily. Also at risk are people whose immune system is suppressed by diseases such as cancer, kidney failure requiring dialysis, diabetes, AIDS, chronic lung disease, or heart failure. Those who take drugs that suppress the immune system such as prednisone, azathioprine, or cyclosporine are also at higher risk.

The bacterium has been found in cooling towers and evaporative condensers of large air conditioning systems. Such systems have been associated with outbreaks of disease.

Cases have been identified throughout the United States and in several foreign countries. It likely occurs worldwide.

 It is estimated that around 10,000 people develop the disease each year in the United States. An additional unknown number are infected with Legionella bacteria but have only a minor illness or no illness at all. The disease can occur in outbreaks or as single cases.