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Making Sense of ... Legionellosis




What is legionellosis?

Legionellosis is an infection caused by the Legionella pneumophila bacterium, which was first identified as recently as 1976, following an outbreak of pneumonia at a convention of the American Legion in Philadelphia.

Legionellosis is occurs as Legionnaires' disease, a serious infection which includes pneumonia, and Pontiac fever, a much milder illness.

Where is legionellosis usually found?

The Legionella bacteria occur naturally, usually in water. The bacteria thrive in warm water, and are very much at home in industrial-size air conditioning systems, cooling towers, hot water tanks, and large pipe networks.

How common is legionellosis?

Legionella is an ubiquitous bacterium, a perennial threat to public health; occurrences of Legionnaire's disease are sporadic but larger outbreaks can occur, such as those related to tourist accommodations, from hotels to cruise ships.

How is legionellosis transmitted?

Legionella is an opportunistic infection; the bacterium survives readily in many water systems; high bacterial load might be an important variable related to disease's occurrence in association to long-term exposure; delivery via water vapour (eg in showers) appears to make infection more likely.

Can legionellosis be spread from person-to-person?

No. The amount of infection delivered into the atmosphere by an infected person does not appear to present a real risk to others. Where outbreaks have occurred, only a proportion of those at risk actually develop symptoms, suggesting that the body can resist fairly high levels of droplet infection, in most cases.

It is possible to envisage a situation in which an immunosuppressed person who has prolonged close contact with an infected person in a warm, damp environment might be at some risk - but it's pretty unlikely, and there is no evidence of such an event having occurred.

Who is most at risk from legionellosis?

Older people, smokers, and those living with a chronic lung condition do have an increased risk.

As with all infections, people with damaged immune systems (eg due to cancer, diabetes, or renal failure) are also more likely to become infected. People who are immunosuppressed, (eg following organ transplant or cancer chemotherapy) are also at increased risk.

What are the symptoms of legionellosis?

People with Legionnaires' disease usually have fever, chills, and a cough, which might be dry or might produce sputum. These symptoms may be accompanied by muscle aches, headache, tiredness, loss of appetite, and (occasionally) diarrhoea. Temperature may reach 39oC, and chest x-rays will usually confirm pneumonia.

Persons with Pontiac fever, the non-pneumonic form, present with an acute, self-limiting influenza-like illness. The incubation period varies from a few hours up to a couple of days. The main symptoms are fever, chills, headache, malaise and muscle pain. No deaths have been associated with this type of infection, which usually resolves without treatment after 2 - 5 days.

What are the long term effects of legionellosis?

Legionella-induced pneumonia is a serious illness, with a high mortality rate if not diagnosed and treated rapidly. recovery can be slow, especially in older people, and long-term effects may include pulmonary fibrosis and functional impairment of the lung.

What is the mortality rate for legionellosis?

The mortality rate has been recorded between five per cent and 30 per cent among those who have been treated, and as high as 80 per cent in untreated patients.

How is legionellosis diagnosed?

Many people become infected with the bacteria with mild symptoms or no symptoms at all; so many cases may go undiagnosed.

Clinical examination and chest xray will suggest a diagnosis of pneumonia, but a specific diagnosis must be confirmed in the laboratory by isolating the legionella bacteria from sputum or other samples.

Is there a treatment for legionellosis?

As with any serious respiratory infection, management involves supoportive measures, which may include physiotherapy, oxygen and even assisted respiration; specific treatment consists of antibiotics, which may depend on the laborartory culture and sensitivity tests. Antibiotics used are usually macrolides (for example, azithromycin) or quinolones (such as ciprofloxacin). Tetracyclines may also be used. Erythromycin was initially the antibiotic of choice, but has largely been replaced by more potent and less toxic antibiotics.

Is there a legionellosis vaccine?

There is no vaccine for legionellosis.

Can legionellosis be controlled environmentally?

Legionnaires' disease was not identified until 1976; since then, extensive research has shown that it's impact has been helped by the technology surrounding urban living.

Equipment that supports Legionella - or its spread - can include:

  • Water features: artificial fountains and water displays, such as those found in shopping centers, restaurants and other modern buildings
  • Cooling plant: industrial strength air conditioning, climate control and refrigeration equipment, found at hospitals, schools, hotels, office blocks ... any modern workplace.
  • Car washes, particularly those that use recirculated water, especially for rinsing.
  • Showers: especially communal, frequently used showers and those used over long periods with limited ventilation.
  • Industrial cleaning, particularly where rinsing or blowing processes are involved.
  • Humidification systems, including indoor growing facilities, industrial sites such as paint booths.

In each case, the processes described may accelerate Legionella pneumophila development, aerosolization, or droplet spread.

Is there legal protection for workers and others?

Now that the dangers of Legionella pneumophila are known, there is a general duty of care by those responsible for such risks, and is some countries, specific regulations to reduce the risks. Workers, authorized visitors (eg swimming pool users), and the public (eg those walking beneath air conditioning outlets) are entitled to a safe environment - or clear and specific warnings of dangers.

Legal protection may include health and safety at work laws, designation of dangerous substances or other laws, depending on the country.

Measures required or implied by law may include:

  • Designing sytems such that water is not undisturbed for long periods.
  • Systems and water storage facilities should be protected from contamination, and periodically inspected, cleaned and disinfected.
  • Water temperatures of 20oC to 45oC should be avoided; hot water stored at or above at 60oC, circulating at or above 50oC.
  • Fittings and equipment in water systems should be maintained as fit for purpose, using safe and reliable materials.
  • Water systems must be well designed, maintained and operated to prevent the escape of fine water droplets.
  • Water should be treated to prevent scale, corrosion and microbial growth.
  • Dry cooling systems, rather than cooling towers, may be a safer option in many cases.

What can be learned from history?

The panic-led investigations into the Veteran's outbreak of disease in Philadelphia eventually isolated the microbe, the investigation involving more than a little luck. One factor in the delays was the assumption that there was no such thing as an undiscovered bacterium; another that any bacteria causing such havoc would thrive at or near human body temperature, rather than much higher temperatures. Subsequest investigations proved that the disease was by no means new, and once the chain of events was understood, valuable lessons about urban living and its hazards were identified.

"Elimination of legionnaires' disease is not achievable, so vigilance combined with a balanced response based on an understanding of costs and benefits is required" - Raj S Bhopal, professor of public health.

Bibliography and Further Information Sources

If this article hasn't answered your question, email me at the address below, and I'll try to get the information you seek. I regret I cannot assist with individual cases or essays and school projects, but if it's something I've missed, I'll be happy to try and help.

Article written by Andrew Heenan BA (Hons), RGN, RMN

First Published: 10 November 2006
Last updated: 18 March 2012
© Andrew Heenan 2006 et seq


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