Legionellosis or Legionnaires' disease is caused by common Legionella bacteria, which live in the environment, especially in soil, compost, potting mix muds and any type of water system (for example, spa pools, hot water tanks).
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Legionellosis is not common in New Zealand. Most people’s natural immunity stops them from getting ill when exposed to Legionella bacteria.
All ages can be affected but the disease mainly affects people over 50 years of age, and generally men more than women. Smokers or ex-smokers, heavy drinkers and people with a compromised immune system are at a higher risk.
Susceptible people catch legionellosis by breathing in airborne particles from a water source that contains Legionella bacteria, or after inhaling dust from soil. Once in the lungs the bacteria multiply and may cause a mild illness without pneumonia called Pontiac fever or a more severe illness with pneumonia (Legionnaires’ disease) The infection is not contagious and can't be caught from another person.
- Institute for Environmental Science and Research: Legionella numbers on the rise.
ESR microbiologist David Harte explains a recent rise in cases, and the need for gardeners to be aware of the risks of handling potting mix and compost.
- Auckland Regional Public Health Service: Fact Sheet - Legionellosis.
- Regional Public Health (Greater Wellington region): Legionellosis (Legionnaires’ disease) Fact Sheet.
Symptoms include a 'flu-like' illness with:
- rapid onset fever
- muscle aches
- loss of appetite
- chest pain
- dry cough leading to pneumonia.
Nausea, vomiting and diarrhoea sometimes occur and mental confusion and disorientation may develop. The illness progressively worsens over several days.
People with Pontiac fever generally recover in 2–5 days without treatment.
Legionnaires’ disease is treated with antibiotics. It is important to receive treatment early as a delay may result in a worse outcome.
When working in the garden, protect yourself:
- wear a face mask and gloves
- open bags away from your face
- work in a well-ventilated area
- dampen soil/compost before use
- wash your hands when you’re finished.
Legionella bacteria cannot survive in water at 60°C or above. Ensure your hot water cylinder is set to at least 60°C and use mixing valves to ensure a safe temperature at the tap to prevent scalding.
Further information on working safely with soil, compost and potting mix, and preventing Legionnaires’ Disease from cooling towers and evaporative condensers, is available at:
Legionnaires' disease - WorkSafe website.