Legionellosis Fall '12

From GGCWiki
Jump to: navigation, search



Legionnaires' disease acquired its name in July 1976 when an outbreak of pneumonia occurred among people attending the 58th convention of the American Legion at the Bellevue-Stratford Hotel in Philadelphia. Of the 182 people infected, 29 died. A bacterium that would later be named L pneumophila was isolated from different organ tissues of guinea pigs inoculated with lung tissue samples from 4 individuals who died. Although this pathogen was not identified until 1976, retrospective analysis suggests that L pneumophila may have been responsible for previous pneumonia epidemics in Philadelphia; Washington, DC; and Minnesota.[5].

  • Found in natural and man-made water systems or aquatic environments
    • This includes showers, mist machines in grocery stores, cooling towers, whirpool spas, industrial plants and evaporative condensers[2]
  • Legionella organisms are spread throughout the environment by aerosols in the wind. Inhalation of these aerosols causes the bacteria to enter the body and cause infection [3]
    • unlike other pathogens that cause bacterial pneumonia, L. pneumophila do not inhabit the upper respiratory tract. Once inhaled, they are small enough to avoid the defenses of the upper airway.
    • In the lung, pulmonary alveolar macrophages (macrophages of the air sacs in the lung) and sometimes type II alveolar epithelial cells take up L. pneumophila where it begins to grow intracellularly. It seems intracellular infection is necessary for producing infection because mutants of L. pneumophila are unable to cause disease.[6]
  • This disease is not contagious. There is no transmission of this disease between humans or humans and animals
    • Pregnant women do not need to worry about their babies being infected with this disease [2]
    • Less severe in children
  • Middle-aged or older men, in particular those who smoke or drink heavily are generally prone to this illness
    • Individuals who suffer with a chronic illness.[5]
    • Individuals with compromised immune systems due to diseases such as cancer, diabetes, or kidney failure are also more likely to get sick [1]
    • Individuals who smoke have a greater chance of getting infected due to impaired cilia in the respiratory tract. The gag reflex is bypassed due to impaired cilia and the bacteria is able to enter the respiratory tract [4]
    • Legionella enters the lung via aspiration (choking) when foreign particles including bacteria escape the gag reflex and fall directly into the respiratory tract (windpipe and lung) [6]
  • There is little recurrence of this disease


L. pneumophila is a gram-negative, facultative intracellular coccobacilli, non-encapsulated, aerobic bacillus with a single, polar flagellum. The organism is approximately 2µm in length and 0.3-0.9µm in width 2–20 microns in length [2], but in nutrient-deficient media, it may become long and filamentous. It is surrounded by a gram-negative cell wall and pili are sometimes identified. The cell envelope is composed of branched-chain fatty acids and distinctive ubiquinones, whose structural differences have been used to classify different Legionella species. The outer-membrane is comprised of a lipopolysaccharide (LPS), which is “fully sequenced and found to have several novel features which have pathophysiologic consequence” and is noticeably less endotoxic than enterobacterial LPS since it has weak interactions with the CD14 receptor on monocytes, The interactions are probably inhibited by the long-chain fatty acids of L. pneumophila lipid A, which are two times the length of enterobacterial lipid A. A single, major protein also makes up the outer membrane and functions as a porin and as a target for human complement fixation. L. pneumophila serogroup 1LPS also has a repeating O antigen. It is a homopolymer of an uncommon sugar, called legionaminic acid. ”LPS is the immunodominant antigen of the Legionellaceae, and the O antigen is the determinant of serogroup specificity within the genus.”[2]

    • Legionella organisms are readily found in natural aquatic bodies and some species have been recovered from soil[5]
    • They are often not detected by simple gram staining and require other means of growth in the lab
    • In order for this bacteria to grow and reproduce it needs the right temperature and the right food.
    • his bacteria feeds on algae, sludge, rust and lime scale [6]
    • These nutrients for growth of bacteria are mostly found in water reservoirs
  • These tough organisms can survive in a wide range of conditionso,They can withstand temperatures of 0–68°C and a pH range of 5–8.5. [2]
  • Legionella virus is most commonly detected in rivers, lakes, and streams.
  • Legionella and other microorganisms become attached to surfaces in an aquatic environment forming a biofilm.
    • Interestingly, the growth of other environmental organisms is stimulated by organic sediment, which in turn leads to the formation of by-products that stimulate the growth of Legionella.[5]
    • Legionella has been shown to attach to and colonize various materials found in water systems including plastics, rubber, and wood[5]
    • Legionella can also attach to the respiratory tract and multiply quickly.
  • The incubation period of legionnaires’ disease is between 2 and 14 days

The Taxonomy of Legionellae

Taxonomy Classification
Domain Bacteria
Kingdom Proteobacteria
Phylum Gammaproteobacteri
Class Spirochaetes
Order Legionellales
Family Legionellacaea
Genus Legionella
Species Legionella pneumophila

Scientific name

Legionella pneumophilia



Legionellosis refers to 2 distinct clinical syndromes: Legionnaires disease, which most often manifests as severe pneumonia accompanied by multisystemic disease, and Pontiac fever, which is an acute, febrile, self-limited, viral-like illness

  • Individuals with legionnaires disease will get pneumonia, patients with severe pneumonia should be tested for legionellosis.[2]
  • Incubation period: 2 to 14 days
  • Flu-like symptoms which include:
    • Loss of appetite
    • Tiredness
    • Body aches
    • Headache
    • Chills and rising fever

legionnaires disease can be hard to diagnose at first. Chest X-rays are needed to find the pneumonia caused by the bacteria, and other tests can be done on sputum (phlegm), as well as blood or urine to find evidence of the bacteria in the body.[2]


The fatality rate of Legionnaires' disease ranges from 5% to 30% during various outbreaks and approaches 50% for nosocomial infections, especially when treatment with antibiotics is delayed. According to the journal Infection Control and Hospital Epidemiology, hospital-acquired Legionella pneumonia has a fatality rate of 28%, and the principal source of infection in such cases is the drinking-water distribution system. There are about 8,000 to 18,000 cases of Legionnaires’ disease each year in the United States, according to the Bureau of Communicable Disease Control.Much has been learned about the epidemiology of Legionnaires' disease since the organism was first identified in 1976. National surveillance systems and research studies were established early, and in recent years improved ascertainment and changes in clinical methods of diagnosis have contributed to an upsurge in reported cases in many countries. Environmental studies continue to identify novel sources of infection, leading to regular revisions of guidelines and regulations. Between 1995 and 2005 over 32,000 cases of Legionnaires' disease and more than 600 outbreaks were reported to the European Working Group for Legionella Infections (EWGLI). In the future, there may be an increase in cases as the population becomes more elderly.[2] There is a shortage of data on Legionella in developing countries and it is likely that Legionella-related illness is underdiagnosed worldwide.[39] Improvements in diagnosis and surveillance in developing countries would be expected to reveal far higher levels of morbidity and mortality than are currently recognised. Similarly, improved diagnosis of human illness related to legionella species and serogroups other than Legionella pneumophila would improve knowledge about their incidence and spread.

  • An estimate of over 25,000 cases of the illness occur each year and cause more than 4,000 deaths [6]
  • Legionnaires' disease, which occurs in approximately 5 percent or less of people who are exposed, Pontiac fever will occur in approximately 90 percent of those exposed[5]
    • Approximately 1,000 cases are reported annually to the CDC [1]
    • It is estimated that in the United States there are between 10,000 and 50,000 cases of Legionnaires' disease each year,
    • between 8,000 and 18,000 people are hospitalized with Legionnaires' disease in the U.S.[4]
    • Most infections are not diagnosed or reported
    • More illness is usually found in the summer and early fall, but it can happen any time of year[4]


  • There is no vaccine currently available for Legionnaires’ disease.
  • To be safe, chest X-rays should be done in order to identify any lung tissue damage

L. pneumophila is not sensitive to antimicrobials (e.g., penicillin, cephalosporin, aminoglycosides) that are excluded by the plasma membrane, and therefore, it is treated only with Antibiotics.[5]

    • Erythromycin, the former antibiotic of choice, has been replaced by more potent and less toxic antibiotics.
    • The two most potent classes of antibiotic are:
    • Quinolones (ciprofloxacin, levofloxacin, moxifloxacin, or gatifloxacin) [6]
    • Macrolides (azithromycin, clarithromycin, or erythromycin) [6]
      • Other agents that have been shown to be effective include tetracycline, doxycycline, minocycline, trimethoprim- sulfamethoxazole.
      • Macrolides are used in all age groups while tetracyclines are prescribed for children above the age of 12 and quinolones above the age of 18. Rifampicin can be used in combination with a quinolone or macrolide. It is uncertain whether rifampicin is an effective antibiotic to take for treatment.The Infectious Diseases Society of America does not recommend the usage of rifampicin with added regimens.[6] Tetracyclines and erythromycin led to improved outcomes compared to other antibiotics in the original American Legion outbreak. These antibiotics are effective because they have excellent intracellular penetration in Legionella infected cells.
    • Medication Sideffects-nausea, dizziness, headaches, loss of appetite, and chest pains [5]
  • Prevention of this disease includes proper maintenance of cooling, heating, and plumbing systems [4]
  • Outbreaks can usually be controlled by identifying and cleaning contaminated water sources [2]

Related Diseases/Sequelae

  • A milder infection caused by the same type of Legionella bacteria is called Pontiac Fever . The symptoms of Pontiac Fever usually last for 2 to 5 days and may also include fever, headaches, and muscle aches; however, there is no pneumonia. Symptoms go away on their own without treatment and without causing further problems.
    • Pontiac Fever and Legionnaires' disease may also be called "Legionellosis" (LEE-juh-nuh-low-sis) separately or together
  • Complications and sequelae of Legionnaires' disease from the Diseases Database include:
    • Peripheral neuropathy
    • Proteinuria
    • Respiratory failure
    • Lymphocytopenia
    • Hepatocellular jaundice
    • Brain failure
    • Hyponatraemia
    • Pancytopenia
    • Pontiac fever
    • Haematuria
    • Diarrhoea
    • Atypical pneumonia


1) http://www.cdc.gov/legionella/

2) Legionella: State of the Art 30 Years After Its Recognition By Nicholas P. Cianciotto

3) legionella and the prevention of legionellosis http://www.who.int/water_sanitation_health/emerging/legionella.pdf

4) Hicks, Lauri A., Laurel E. Garrison, and George E. Nelson. "Legionellosis--United States, 2000-2009." Jama 306.15 (2011): 1645-1647. General Science Full Text (H.W. Wilson). Web. 27 Oct. 2012.

5) Whiley, Harriet, and Richard Bentham. "Legionella Iongbeachae And Legionellosis." Emerging Infectious Diseases 17.4 (2011): 579-583. General Science Full Text (H.W. Wilson). Web. 27 Oct. 2012.

6) Lam, Meng Chon, Li Wei Ang, and Ai Ling Tan. "Epidemiology And Control Of Legionellosis, Singapore." Emerging Infectious Diseases 17.7 (2011): 1209-1215. General Science Full Text (H.W. Wilson). Web. 27 Oct. 2012.

Personal tools