The 1976 American Legion Convention marked the discovery of Legionnaires' disease, a syndrome of pneumonia caused by Legionella. Many people became sick at this convention which sparked an investigation to uncover the cause. Legionella is an aerobic gram-negative bacillus that is spread through aerosolized water particles. It is a common cause of community-acquired and hospital-acquired pneumonia.
The family Legionellaceae has more than 50 species and more than 70 serogroups; the L. pneumophila serogroup is the most common. This bacterium grows best on buffered charcoal yeast extract agar, which is a specialized media. It inhibits the growth of other bacteria.
L. pneumophila is found in large bodies of water including streams and lakes. However, its growth is increased in the presence of human-made reservoirs. Risk factors include cigarette smoking and chronic lung disease.
The bacterium binds to respiratory epithelial cells and alveolar macrophages after which it enters the cell. Once it has gained entry into the cell, it inhibits phagosome-lysosome fusion, thereby promoting its proliferation.
Legionellae histopathologic lesions are typically found in the alveoli with polymorphonuclear cells and macrophages and in the intestinal lining.
The length of time between exposure and symptom onset is two to 10 days but may be up to 20. Among those exposed, between 0.1% to 5% develop the disease, while among those patients in the hospital, 0.4% to 14% develop the disease.
Patients present with fever, chills, and a dry or wet cough producing sputum. One-third of those affected cough up blood. Some also have muscle aches, headache, tiredness, loss of appetite, loss of coordination (ataxia), chest pain, or diarrhea and vomiting, and neurological symptoms including confusion and impaired cognition. Relative bradycardia also may be present, which is low or low-normal heart rate despite the presence of a fever.
Early diagnosis of Legionnaires' disease has shown to decrease mortality. Therefore, early diagnosis and treatment are important for survival. In patients where Legionella is suspected, urine antigen testing and sputum culture are recommended. Urine antigen testing has proven to be a quick diagnostic test with a sensitivity of more than 85% and specificity of more than 99%. However, it only tests for Legionella pneumophila serogroup, the most common serogroup to cause infection. Sputum culture takes three to five days to grow; however, this can identify other serotypes or species if present.
Chest X-ray - May show pneumonia with consolidation at the base of the lungs.
Expect the following:
Expect respiratory failure, bilateral pneumonia, pulmonary infiltrates, and the presence of at least two of the following:
Given that this is an intracellular organism, antibiotics should be chosen that would be able to enter the cell effectively. The recommended classes of antibiotics include fluoroquinolones, macrolides, and rifampin. Either Levofloxacin 750 mg, one tablet for seven to ten days, or Azithromycin, 1 gm on day one followed by 500 mg one tablet once a day for seven to 10 days, are advised. Parenteral therapy is advised initially as the patient may not tolerate antibiotics given by mouth because of potential gastrointestinal symptoms. Immunocompromised patients, especially transplant patients, should preferably be treated for 21 days with fluoroquinolones. Macrolides would not be recommended here as they can interfere with immunosuppressant agents.
To prevent the infection, most hospitals across the country perform frequent testing of their water supply for Legionella. Proper decontamination of the water supply is recommended.
Patients with Legionella pneumonia are not typically co-infected with other organisms. The differential diagnoses include atypical pathogens, Chlamydophila pneumoniae, tularemia, and Coxiella burnetii. L. pneumophila bacterium is a definite pathogen; its isolation indicates infection.
The differential diagnosis of Legionnaires disease includes:
The prognosis of patients with Legionnaire's disease depends on patient comorbidity, when the condition was diagnosed and how soon the treatment was instituted. In seniors, the mortality rates can vary from 10-50%.
Respiratory failure is a common cause of death.
Legionnaire's disease is usually managed as an inpatient. Some patients may require total parenteral antibiotics, assistance from mechanical ventilation and even enteral nutrition. close monitoring is required as sudden respiratory distress is common.
Once a diagnosis of Legionella pneumonia is made, one must identify the source to prevent other patients from acquiring the organism. The air-conditioning system and nebulizing devices must be checked to identify the source of the bacteria.
Disinfection of the water by heating and use of UV light is known to kill the organism.
Multiple outbreaks can be traced back to water supplies. The most recent was in 2015, and it involved multiple U.S. states. The outbreak was controlled with timely and proper testing and decontamination of the local water sources.
Legionella pneumonia is a serious respiratory tract infection which usually affects the elderly. If the diagnosis is missed or treatment is delayed the morbidity and mortality are very high. Learned evidence-based experience from previous outbreaks reveals that an interprofessional group of healthcare workers is vital to help decrease the morbidity of the infection. Even if a single case is diagnosed, urgent set up of a multidisciplinary team is necessary to determine the source of the outbreak. The organism is known to rapidly disseminate via air droplets and can quickly infect many people.
The team should include a pulmonologist, infectious disease specialist, critical care specialist and an internist. The nurses play a vital role in the monitoring of the patient in the ICU. (Level V) The pharmacist has to be up to date on the current antibiotics used to treat the infection and be aware of alternatives in case of resistance or patient intolerance.
The outcomes for patients with Legionella pneumonia do vary, but despite treatment, mortality rates of 5-15% are reported. (Level V) There should be no delay in treatment as the infection is rapidly progressive and can result in multiorgan failure. Evidence-based medicine reveals that only through an integrated, streamlined approach can the mortality be reduced.