Legionellosis
Legionellosis Surveillance, Allegheny County, 2020-22
Legionella is a bacterium that can cause two types of illnesses in people: Legionnaires’ disease and Pontiac Fever.
Legionnaires’ disease is a type of pneumonia, diagnosed either by symptoms or by chest X-ray. Symptoms of Legionnaires’ disease may include fever, muscle aches, and shortness of breath that begin two days to 14 days after exposure to Legionella. Left untreated, Legionnaires’ disease can result in lung failure and death. Nearly one in 10 people who contract Legionnaires’ disease dies.1 Older individuals, along with those who have weakened immune systems or damaged lungs from smoking or other reasons, are most at risk.
Pontiac Fever is a milder illness that presents with fever and muscle aches that begin a few hours to a few days after exposure to Legionella.
Legionella bacteria are found naturally in freshwater (e.g. lakes and streams). Legionellosis becomes a public health concern when Legionella bacteria start to grow and spread in building water systems such as cooling towers, hot water tanks and heaters, large complex plumbing systems, showerheads and sink faucets, and hot tubs.
Below are frequently asked questions about legionellosis, along with a summary of cases reported to the Allegheny County Health Department (ACHD).
How are Legionella bacteria transmitted?
Legionella can be transmitted by water if the bacteria grow and spread in building water systems. Legionellosis primarily occurs when people breathe in small droplets of water that contain the bacteria. This disease can also be contracted by drinking water containing Legionella bacteria that go into the lungs. In general, legionellosis does not spread from person to person.
How often does legionellosis occur?
In the United States, legionellosis has been on the rise since 2000. In 2018, health departments in the US reported almost 10,000 cases of Legionnaires’ disease, but it is thought this disease is vastly underreported. The true incidence of disease may be about twice as high than what is reported.2 Although cases of legionellosis can occur any time of year, most cases tend to occur during the summer and early fall seasons.
Patients being treated at healthcare facilities, such as hospitals or long-term care facilities, are at higher risk for Legionella infection, given they often have weak immune systems. The CDC reports one in four patients receiving treatment at a healthcare facility who becomes infected with Legionella will die. 1
How is legionellosis monitored?
Clinicians and other professional staff at healthcare facilities should maintain a high level of suspicion for legionellosis and should immediately test patients for Legionella if they develop pneumonia while in the hospital. Healthcare providers must report legionellosis within 24 hours of identifying a case. Case reports submitted to ACHD are used to identify clusters of disease in time and location and monitor the incidence of legionellosis acquired in healthcare facilities and in the community.
How often does legionellosis occur in Allegheny County?
An average of 76 confirmed Legionnaires’ disease cases per year were reported among Allegheny County residents from 2013 to 2022 (Figure 1). The number of reported cases ranged from 43 cases to 97 cases per year.
In 2020-2022, there were 159 cases of Legionnaires’ disease reported in Allegheny County. Among these cases, 97% were hospitalized and 8% died. Most (77%) of the cases did not spend any time in a healthcare facility in the 14 days prior to onset (Figure 2). About 9% of cases were classified as “possible” healthcare associated cases, having spent a portion of the 14 days prior to onset in at least one healthcare facility. Around 2% of cases were classified as a “presumptive” healthcare associated case, having had a continuous stay in a healthcare facility for at least 10 of the 14 days prior to onset. The remaining 12% of cases could not be classified due to missing information.
Cases in 2020-2022 occurred most frequently among males (60%) and occurred most often in white individuals (75%). Adults 60 years of age and older were at highest risk for disease (Figure 3).
Among the cases with available data, 30% were current smokers, 28% were previous smokers, 28% had never smoked, and 14% had unknown smoking status. Most cases occurred during the summer and early fall seasons (Figure 4).
How is legionellosis prevented?
Maintaining building water systems and implementing Legionella water management programs can prevent the spread of Legionella. According to the CDC, effective water management includes maintenance of water temperatures that are not suitable for Legionella growth, minimizing the potential for water stagnation, establishing satisfactory disinfection methods, and preserving apparatuses that require water to prevent sediment, scale, corrosion, and biofilm.3 Elements of a Legionella water management plan include creating an outline of the building water systems, detecting areas of the building where growth and spread of Legionella is likely, and determining best practices for implementing control measures and monitoring them. Further elements include identifying additional interventions when controls measures are not sufficient, continually verifying and validating the program, and recording and informing the water management team of all activities completed. See the CDC’s toolkit for more information about developing a water management plan to reduce Legionella growth and spread in building water systems and devices.3
References
[1] Centers for Disease Control and Prevention. Legionella Diagnosis, Treatment, and Complications. Atlanta, GA. National Center for Immunization and Respiratory Diseases, Division of Bacterial Diseases. Available at: Legionnaires’ Disease Diagnosis and Treatment | CDC
[2] Centers for Disease Control and Prevention. Legionella (Legionnaires’ Disease and Pontiac Fever). Atlanta, GA. National Center for Immunization and Respiratory Diseases, Division of Bacterial Diseases. Available at: Legionnaires’ Disease, Pontiac Fever Fast Facts | CDC
[3] Centers for Disease Control and Prevention. Developing a Water Management Program to Reduce Legionella Growth & Spread in Buildings. Atlanta, GA. National Center for Immunization and Respiratory Diseases, Division of Bacterial Diseases. Available at: Legionella Toolkit-Version 1.1-June 24, 2021 (cdc.gov)