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 symptoms:
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 following:
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.