Despite only having been identified some 25 years ago, Legionella pneumophila (the causative agent of Legionnaires’ Disease) is no new organism. Medical history is littered with evidence that this organism has wreaked havoc long before people knew its identity. Every year about 5-10% of pneumonia cases are caused by this creature, and the mortality rate can soar to as high as 30% if untreated. Legionella testing is critical.
A.D. Scott provide Legionella testing throughout Durham, Newcastle, Gateshead, Hexham, Berwick, Stanley, Consett, Fenham, Sunderland, Ponteland and Chester le Street.
The bacteria’s evolution enabled it to exploit modern technology as means of propagation and so Legionnaires’ Disease is not an unfamiliar disease to most of us. However, for many, there are still unanswered questions; such as, how can technology favour a dangerous organism, and – more importantly – how safe are we from this airborne threat?
What is Legionella
Legionella is a Gram negative, rod-shaped bacteria measuring about 0.3-0.9 microns by 1.5-5 microns. It is an aerobic microbe, meaning that it requires oxygen to live, and has unusual nutritional requirements – high levels of the amino acid cysteine, inorganic iron and low concentrations of salt – as opposed to a large number of other pathogens. It is also unusually tolerant to high levels of chlorine, low pH and high temperatures (they grow nicely at temperatures between 28 and 45 degrees Celsius) – all of which would strike down the normal pathogen.
There are currently at least 34 species of Legionella, and more than 23 serogroups of L. pneumophila. Serogroup 1 is responsible for more than 80% of all Legionella infections; however serogroups 4 – 6 and other species such as L. bozemanii, L. longbeachae and L. maceachernii have been known to cause Legionnaires’ Disease as well.
Where can Legionella be found?
Legionella is ubiquitous in natural freshwater sources such as rivers, ponds and hot springs, usually living as parasites of a number of amoebae. They can also be found in the waters of air-conditioning cooling towers, spas, fountains and potable water sources such as taps, faucets and showerheads. L. longbeachae is usually found in soil, and is transmitted in a most fascinating fashion, which will be discussed later.
Who does Legionella infect?
In the environment, Legionella parasitises free-living amoebae such as Naegleria and Hartmanella. It also infects macrophages and a number of other components of the human cell-mediated immune system.
Scientists have also isolated L. pneumophila from calves who had died of pneumonia. In the second case, fatal pneumonia caused by L. pneumophila was determined as the cause of death.
How does Legionella infect us?
The primary mode of transmission is by inhalation of aerosolised water droplets containing Legionella. Once inside, it is gobbled up by patrolling alveolar macrophages, who extend a single pseudopod from their cell surface and drag Legionella into them. Under normal circumstances, a ‘captured’ bacteria is subsequently packaged inside a membrane called a phagosome, which will then fuse with a lysosome.
However, Legionella has found a way to stop this fusion from occurring, which means that this parasitic little bacteria is now safely tucked away in a little parcel in a large white blood cell that restlessly roams about the lungs. Now that it does not need to fear being attacked by other components of the immune system, it can begin to multiply inside the macrophage, using the cell as a mobile home and the stuff inside it as food. Eventually, when the children and great-grandchildren of the original Legionella have exhausted the food supply, they burst open the macrophage, thus killing it, and surge out in search of new homes. This will continue to go on and on until they are stopped, or until they have done immense damage to the human host.
What are the symptoms of infection by Legionella?
The less severe form of Legionella infection is Pontiac Fever, which manifests itself as a self-limiting flu-like illness. The incubation period is remarkably short – in terms of hours to several days – and symptoms will include malaise, muscle aches (myalgia), fever, chills and headache. Patients will, however, typically recover completely within one week.
Legionnaires’ Disease is the more severe manifestation of Legionella infection. The incubation period for Legionnaires’ Disease is 2 to ten days. Symptoms typically include a dry (non-productive) cough and difficulty in breathing, as well as flu-like symptoms such as fever, headache, chills, myalgia and overwhelming lethargy. The onset of pneumonia is abrupt. Chest X-rays will reveal signs of pneumonia, either in a distinct area (‘lobar’) or in a ‘patchy’ pattern throughout the lungs. Sputum is occasionally produced, often containing inflammation, but Gram staining will reveal no bacteria in the sputum. Failure of the pneumonia to respond to traditional pneumonia-combating antibiotics such as expanded-spectrum cephalosporins and aminoglycosides usually confirms the disease. If the patient is not treated by this stage, prognosis is poor.
Occasionally, other complications may arise from infection by Legionella, including:
Heart: pericarditis, endocarditis, myocarditis
Lungs: pleural empyema
Kidneys: pyelonephritis, acute renal failure
Gastrointestinal tract: hepatic abscess, diarrhoea, GI tract-related abscesses
Other parts of the body: peritonitis, cellulites, skin rashes, encephalitis, myoglobinuria
Lately, infection by Legionella has also been linked to acute purulent arthritis.