RECENT MEDIA REPORTS of water contamination have raised consumer awareness of not only toxins and chemicals that can pollute the water supply but also of waterborne infections. One such infection is Legionnaires' disease, which is caused by aspirating water or inhaling aerosolized water droplets containing the Gram-negative Legionella bacteria. The bacteria can infect the lungs and lead to pneumonia.1,2
Most cases of Legionnaires' disease are from Legionella pneumophila serogroup 1. However, over 50 strains of Legionella have been identified, and approximately 30 are infectious for humans.1Legionella bacteria are naturally found in fresh water at very low levels unlikely to cause illness. However, the bacteria will multiply quickly in improperly treated water kept at warm temperatures.
Legionnaires' disease isn't spread from person to person. When an outbreak occurs in a particular geographic area, it means multiple individuals were exposed to a common contaminated source.2 The outbreak that gave the disease its name occurred at a Legionnaires' convention in Philadelphia in 1976. Other outbreaks have been reported in New York City, Quincy, Illinois, San Quentin, California, and Genesee County, Michigan.3
Only 5% of those exposed to Legionella bacteria will develop Legionnaires' disease; 90% of those exposed will develop a less severe version of the infection called Pontiac fever.4 Ultimately, Legionnaires' disease is fatal for 5% to 30% of those with the illness.2 Fatality rates of up to 40% have been reported among healthcare-associated exposures.5,6
Although Legionnaires' disease is a nationally notifiable disease, it's significantly underdiagnosed.1 In fact, data extracted from thorough testing of patients with community-acquired pneumonia lead researchers to estimate that only 5% of actual cases of Legionnaires' disease are reported to the CDC.1 Even with substantial underreporting of the disease, the number of documented cases has increased significantly since 2000. This may reflect an increase in actual cases, improvements in diagnosis and reporting, or a combination of factors.6
The incidence of Legionnaires' disease varies significantly according to the season, with 62% of cases occurring in summer and early fall.1 The increase in the number of new cases of Legionnaires' disease is associated with the increase in both environmental temperature and precipitation associated with global climate change.7 Those at greatest risk are patients over age 50, smokers or former smokers, those with chronic lung disease, and those with compromised or suppressed immune systems.2
Legionnaires' disease is reportable to the public health authorities in all states. Two national surveillance systems, the National Notifiable Disease Surveillance System and the Supplemental Legionnaires Disease Surveillance System, are in place to monitor disease outbreaks.3 Reporting helps track disease burden among various populations as well as determine outbreaks that need to be contained. Healthcare-associated exposures are a particular concern because they can impact a large number of at-risk individuals and are associated with greater morbidity and mortality.3,5 For reporting purposes, ask patients about exposure to aerosolized water droplets, travel, or hospitalizations within the last 14 days.6
Signs and symptoms
Patients with Legionnaires' disease will present with the clinical and radiographic findings of pneumonia usually 2 to 10 days after exposure to the bacteria.2 A prodromal period may occur with headache, myalgia, fatigue, and anorexia. Cough, shortness of breath, and high fever with relative bradycardia are common as the illness progresses. These are also typical signs and symptoms of other bacterial pneumonias, complicating diagnosis and reporting. However, gastrointestinal and neurologic manifestations of infection suggest Legionella infection, particularly if the patient reports a history of hot tub use, travel, or recent hospitalization.1
Patients who develop the less severe form of Legionella infection, Pontiac fever, will have a fever and myalgia, usually within 3 days of exposure, but don't develop pneumonia. Pontiac fever is more frequent among young people and is generally self-limiting.2
The diagnosis of Legionnaires' disease usually involves a chest X-ray, sputum culture, and urinary antigen testing. A culture of lower respiratory tract secretions is still considered the gold standard for detecting Legionnaires' disease.1 In particular circumstances, such as when a rapid diagnosis is necessary, the provider may utilize real-time polymerase chain reaction DNA testing.6 Although healthcare providers use urinary antigen testing in 70% to 80% of cases, be aware that despite its high test sensitivity (80% to 90%) for Legionnaires' disease from L. pneumophila serogroup 1, it has a much lower sensitivity (under 50%) for other strains.6 Therefore, a negative urinary antigen testing doesn't unequivocally rule out Legionnaires' disease.
If your patient is diagnosed with Legionnaires' disease, initiate antibiotic therapy as prescribed in accordance with updated community-acquired pneumonia guidelines.3 The most effective antibiotics include the newer macrolides (especially azithromycin), doxycycline, and quinolones (especially levofloxacin).1,8 Monitor for signs and symptoms of complications such as respiratory failure, renal failure, and central nervous system involvement.6 Patients may require mechanical ventilator support and supplemental oxygenation. Assessing hydration status, particularly among patients with gastrointestinal signs and symptoms, is crucial.6 Closely monitor fever and don't discontinue antibiotic therapy until the patient is normothermic for 48 to 72 hours.6 If patients are discharged on antibiotics, educate them about the importance of completing their regimen. Because Legionnaires' disease isn't transmitted person-to-person, transmission-based precautions aren't necessary.1
Patients with Pontiac fever rarely require antibiotics or hospitalization. However, when detected, it's usually a marker of environmental contamination and nurses should assist with rapid detection measures to avoid additional cases of Legionnaires' disease.1
To prevent Legionnaires' disease, communities should properly treat and maintain water systems. This includes water used for drinking and showering, hot tubs, decorative fountains, and cooling towers used for large air conditioning systems.2 Nurses must be sure to use only sterile water in aerosolizing respiratory therapy equipment and disinfect this equipment appropriately.6
Changing demographics as well as environmental risk factors in developed countries are increasing the number of people at risk for infection.1 These factors include an aging population and the deteriorating water infrastructure in this country. Outbreaks are frequently associated with contamination within complex water systems including those found in hotels, hospitals, and cruise ships.2 Reports indicate that Legionella is detectable in 12% to 70% of hospitals' hot water distribution systems.1
Because the Legionella bacterium is an intracellular parasite, it's even more resistant to chlorine treatment than E. coli.5 Iron corrosion in old pipes consumes chlorine and makes it more difficult to ensure adequate chlorine levels are reached at the tap.9,10 Keeping water below 20° C (68° F) or above 50° C (122° F) can also help stop the replication of the bacteria in water systems.1 Adequate water safety management plans must include regular testing and appropriate treatment in all facilities.