Legionella
Legionella is a bacterium that causes illness in people. Legionella can cause severe pneumonia (Legionnaire’s disease) that can be deadly. It can also cause a milder illness, called Pontiac fever. Pontiac fever was first identified in 1968, but the bacterial cause was not discovered until 1976, during an outbreak at an American Legion convention in Philadelphia. Cases of legionellosis are tracked nationally in an effort to find and curb outbreaks.
Transmission
Legionellosis is spread through contaminated water systems that produce mist that people breathe in. While home and car air-conditioning units do not cool through water, larger commercial buildings often do. The disease does not spread person-to-person. However, decorative fountains, showerheads, sink faucets, hot tubs and cooling towers all produce a water mist that can spread Legionella if the water source is contaminated. On average, the incubation period for Legionnaire’s disease is 2 – 14 days after exposure but may take longer. Incubation time for Pontiac fever, a milder illness, is shorter: a few hours to a few days.
Epidemiology
Most cases of legionellosis are caused by Legionella pneumophila serogroup 1. Because illness is linked to exposure to contaminated water sources, there is a rise in diagnoses in the summer and fall months. However, this may be extended in warmer climates that have fountains and air conditioning units on for longer. In general, there has been a steady rise in cases since 2000. Some groups have higher incidence rates than others: black persons, males, older adults, and those in the Northeast and Midwest regions.
Signs & symptoms
Pontiac fever is characterized by fever, myalgias and headaches; there is no pneumonia. It is generally mild and self-limited without treatment. Legionnaire’s disease typically manifests as a lower respiratory infection with fever and cough, but can also present with shortness of breath, myalgias, headache, altered mental status and gastrointestinal symptoms. Hospitalization is common, and the case-fatality rate is about 10%.
Those with chronic lung diseases, compromised immune systems, current or prior smoking, systemic malignancy and chronic conditions like diabetes, renal failure or liver failure are at increased risk for Legionnaire’s disease.
Diagnosis
Legionellosis is typically diagnosed by laboratory testing only when pneumonia is present. Culture or molecular testing of lower respiratory secretions can detect Legionella. There is also a urinary antigen test which will only identify Legionella pneumophila serogroup 1.
Prevention strategies
The most important way to prevent illness is to keep water sources clean. Building owners should monitor their water quality, looking for bacterial growth. However, private fountains and hot tubs are also at risk of creating fertile ground for Legionella to grow. There are recommended steps to take to keep water in your home safe; your local water company is also a source of information.
Vaccination
There is no vaccine for Legionella.
Treatment
Both macrolides (e.g. azithromycin) and respiratory fluoroquinolones (e.g. levofloxacin) are active against Legionella. In patients who are treated for pneumonia with other antibiotics and don’t improve, clinicians should consider Legionella.
Infection prevention and control
Recommended Personal Protective Equipment (PPE) for legionellosis is standard precautions, because Legionella does not spread person-to-person.
Reporting
Legionellosis is a nationally notifiable condition. Immediately notify state, tribal, local, or territorial health departments (24-hour Epi On Call contact list) about any case of Legionella.
