Legionellosis or Legionnaires' disease is a pneumonia-like human infection caused by gram-negative
bacteria of the genus Legionella. It is viturally impossible to distinguish from pneumonia without diagnostic
laboratory tests.The disease may cause lung abscesses and infections in other organs. Legionnaire's
disease was first recognized in 1976.
The mode of transmission is usually aspiration. Inhaling mist droplets with Legionella is a common cause of
infection. Vapors from water devices colonized with Legionella can transmit the organism. Being directly
sprayed with water is unlikely to cause Legionnaires' disease.
Legionella, in their natural habitat, grow within other organisms. Legionella have frequently been found to
be in very close association, possibly an endosymbiotic relationship with Hartmanella vermiformis,
Tetrahymena thermophila, and Acanthamoeba castellani. The reason why Legionella grow inside these
amoebae is because the bacteria multiply intracellularly, and therefore require the amoebae in order to
reproduce. In humans, the host cell is often killed by the Legionella organism. It is difficult to kill Legionella
bacteria because of their better resistance to many toxic substances while inside the amoebae.
The severity of illness at onset varies from mild nonspecific findings to profound respiratory and/or
multiorgan failure. After an incubation period of 2-10 days, patients may develop the following nonspecific
Respiratory problems may not be present initially but can develop as the disease progresses. Almost all
infected individuals develop a cough, which is initially dry, but may become productive with pus and sputum
and, (in rare cases) blood. Patients may also experience chest pain. Neurologic complaints may include the
Many infected individuals who suffer Legionnaires' disease will experience fatigue for more than a year,
although almost all will recover eventually. Joint pain after recovery is common, but inflamed joints that swell
up are not. The acute symptoms of Legionnaires' disease respond quickly to antibiotic therapy. Yet
weakness and fatigue can persist for months. There is a possibility of persistent diarrhea induced by
antibiotic therapy (Clostridium difficile colitis).
Mortality Rate Estimates:
Healthy individuals given appropriate antibiotics early = 0-9%
Immunocompetent individuals not given appropriate antibiotics early = 20%-35%
Immunosuppressed individuals (transplant patients, cancer patients, etc.) given antibiotics early = 5-20%
Immunosuppressed individuals not given antibiotics early = 40-50%.
A victim's mortality rate is increased by delay in commencing diagnosis and therapy. There is a need for
rapid and reliable diagnostic tests. Efforts to develop Legionella tests have been hampered by the fact that
there are multiple Legionella species, and some of which fall into distinct serogrups. Most tests are
time-consuming and incapable of identifying more than one serogroup at a time. There are 15 serogroups
known just within the Legionella pneumophila species. More than 80% of Legionnaire's disease cases are
attributed to L. pneumophila serogroup1. A test for this organism has been given a strong focus and is of
particular importance. Efforts to speed the diagnosis process had led to the commercially available
Legionella Urinary Antigen Test sold in kit form by IVD Research Inc. The test detects Serogroup1 of
Species L. pneumophila, and it's serogroups 2-5. However, because the majority of infections are caused by
serogroup1, there is yet to be a bank of research samples for the remaining 6-15 serogroups.
Anybody with confirmed Legionnaires' disease must have his or her case reported to the local health
department. Physicians are informed that if the patient contacts pneumonia while in the hospital, tests for
Legionella should be immediately available in-hospital.
Keep in mind that most large buildings and 10% of homes are colonized with Legionella. Legionella can be
contracted, not by mold, but by the water in your home water distribution system. However, drinking water
poses a risk to only some individuals. Individuals with lung disease and smoking are at risk. People with
underlying immune-deficiency diseases, compromised immune systems, or organ transplant recipients are
also at higher risk. These at-risk individuals can boil water, let it cool and then refrigerate it for drinking.
The Center of Disease Control (CDC) recommends that when a case of Legionnaires' disease occurs in a
hospital, the hospital water supply should be cultured since this is a likely source. Newborns can contract
Legionnaires' disease, but almost always in the hospital where the hospital water supply is contaminated.
The following countries now recommend routine environmental surveillance for Legionella in hospitals:
Denmark, France, Germany, Taiwan, and the cities of Barcelona, Spain; Pittsburgh, PA; and the State of
Maryland. CDC recommends routine surveillance if transplants are being performed.
Chlorinating water supply is ineffective long-term against Legionella. Recent strategies for destroying the
bacteria, such as passing Ultra Violet light as well as hot water through pipes, has been found to be very
successful but expensive. It is particularly expensive when treating large amounts of water. Scientists are
also trying to find biocides that are toxic to the bacteria, but safe for humans. This research is in its early
stages and so far no biocides have been uncovered. There has been talk of developing a vaccine, but
research is in its early stages. Erythromycin is the first choice antibiotic based on clinical experience.
Rifampicin has been recommended as an additional antibiotic.