Welcome to the Microbiology Information

Legionella are bacteria that are common in the environment such as rivers and lakes as well as artificial water systems which includes hot and cold water systems such as storage tanks, pipework, taps and showers. In the environment the occurrence of legionella in groundwater is also common.

With Legionella we usually associate it with larger water systems such as those in factories, hotels, hospitals and museums, and cooling towers. However, they can also live in smaller water supply systems used in homes and other residential accommodation.

In addition, other potential sources of legionella include spa and whirlpool baths, humidifiers in factories and fire-fighting systems such as sprinklers and hose reels. Legionella can survive in
low temperatures, but thrive at temperatures between 2OoC and 45oC. At high temperatures, greater than 6O0C legionella will be killed.

Legionella causes Legionnaires’ disease and it is a potentially fatal form of pneumonia. It can affect anybody, however the risk is higher for those over 45 years of age, smokers and heavy drinkers, those suffering from chronic respiratory or kidney disease, and people whose immune system is low or impaired.

Legionellosis is the collective name given to the pneumonia-like illnesses caused by legionella bacteria, including the most serious and well-known Legionnaires’ disease, and also the similar but less serious conditions of Pontiac fever and Lochgoilhead fever.

If you suspect an area may have the potential for Legionella, then it is best to get the water tested using an accredited water testing laboratory.

Did you know that it is possible for you to assess the legionella risk yourself. Below are a list of questions you can go through if you do not feel you have the right skills. Alternatively, you can obtain help and advice from a consultant and use them as a form of training.

When you do the risk assessment, consider the following:

1. Are the conditions right for the bacteria to multiply, for example is the water temperature between 20oC and 45oC? This is the ideal temperature growth range?

2. Are there areas where stagnant water occurs (deadlegs), for example pipes to a washing machine or any other appliance that use water and is no longer used? Again growth can occur in stagnant water.

3. Are there infrequently used outlets, for example showers and/or taps?

4. Is there debris in the system, such as rust, sludge or scale (often a problem in old metal cisterns), that could provide food for growing legionella? Remember iron is a substrate used for growth of legionella.

5. Are there thermostatic mixing valves that set a favourable outlet temperature for legionella growth?

6. Are any of your employees, residents, visitors etc vulnerable to infection, eg heavy smokers, older people, or those with low immune system?

If you answered ‘yes’ to any of these questions, I suggest there is an increased risk of your premises being exposed to legionella and may be a risk.

Legionnaires’ disease is an acute bacterial infection of the lower respiratory tract, i.e., a bacterial pneumonia. The disease is a potentially fatal, multi-system respiratory illness with an average mortality rate of 15-20%. Fortunately, it is selective in attack and infects only 2-5% of those appropriately exposed to the bacteria.

• Legionnaires’ disease is a serious illness and not rare. Legionella bacteria are among the top three causes of sporadic, community-acquired pneumonias. American Society for Microbiology News (61:621) (1995) reported that 15-30% of patients admitted to intensive care units with pneumonia had legionellosis. It is also the cause of many hospital-acquired (nosocomial) cases of pneumonia. Many Legionnaires’ disease cases go undiagnosed because the disease is difficult to distinguish from other forms of pneumonia – unless specifically targeted. Even when detected, it often goes unreported to the public health authority, especially if cases are sporadic (one or two-case incidents) and not associated with an outbreak investigation. The under-detecting and under-reporting of Legionnaires’ disease makes its incidence difficult to estimate and why such figures vary widely. The CDC has estimated that the disease infects 10,000 – 15,000 persons annually in the US. OSHA estimates that over 25,000 cases of the illness occur each year, causing more than 4,000 deaths. Still, others estimate as many as 100,000 annual cases.

• Legionnaires’ disease Exposure is most likely to occur via:

1. Inhalation: of aerosols, fine sprays, mists or other microscopic droplets of water (or soil) contaminated with Legionella – providing direct access into the lungs; and/or

2. Aspiration: such as may occur when choking or spontaneously during the drinking, ingesting, swallowing process – allows oral fluids and/or particles to by-pass natural gag reflexes and enter into the respiratory tract and lungs instead of the esophagus and stomach.

Legionella is the name for the genus of bacteria. Legionellae (the plural, referring to more than one Legionella bacterium) are aerobic, non-spore forming, rod-shaped, typically flagellated, gram-negative bacteria. They are common to aquatic, especially warm water, environments and some soils. There are 43 or more identified species of Legionella, with more than half being linked to human disease. Some Legionella species are made up of multiple serogroups, with over 60 serogroups presently identified for the genus. Many of the species serogroups are further differentiated into numbers of subtypes.

Legionellosis is the collective term describing any illness caused by exposure to the bacterial pathogen Legionella. Legionnaires’ disease and Pontiac fever are the two most common types of legionellosis, with Legionnaires’ disease being the more serious and primary one of focus. It is an environmental disease – with the causative agent (Legionella) transmitted from an environmental source (water or soil) to a host. It is not transmitted from person to person – thus, it is not a communicable disease.

Legionella pneumophila (Lp) is one species of Legionella – and is the causative species to more than 90% of legionellosis cases. More than 70% of these cases are attributed to one serogroup of the more than 15 Lp serogroups – Legionella pneumophila serogroup 1 (Lp-1). As it turns out, Lp-1 is the most common isolate recovered from environmental samples. Within Lp-1 are more than 50 subtypes that can be identified by phenotypic or molecular typing methods. Serogroups and subtypes appear to differ as to their particular degree of virulence.

Did you know that Legionnaires’ disease (LD) acquired its name from the media reference given to a
mysterious pneumonia-like illness that afflicted numerous attendees of an American Legion
convention in Philadelphia at the Bellevue-Stratford Hotel during July of 1976. This resulted in an outbreak of illnesses and presented the Pennsylvania Department of Public Health officials with a
recorded 221 cases of a strange respiratory illness contracted by convention (hotel)
attendees and by some hotel pedestrians. Common symptoms included high fever, chills, muscle
pain, headache and eventual development of a dry cough with difficulty in breathing. Some
patients developed patchy lesions in their lungs representative of severe pneumonia. In addition, more
than two-thirds of the patients required hospitalization and 34 eventually died.

Investigation of the outbreak by the Centers for Disease Control and Prevention (Atlanta, GA) led to the eventual discovery of the causative agent, a bacterium, in January of 1977. The bacterium was subsequently named Legionella pneumophila (pneumophila is Greek for lung-loving). It was determined that neither the bacterium nor the disease was new and that Legionella bacteria have been around and causing disease for many years. When reexamined, the CDC found Legionella bacteria in fifty-year old (archived) tissue samples of unsolved and similar-illness cases. So, Legionnaires’ disease was not a new disease discovered in 1976 – just an old one that was finally recognized and named.