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Legionellosis or Legionnaire's 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).

You can catch it 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 cause either pneumonia (Legionnaires’ disease) or an illness without pneumonia called Pontiac fever. The infection is not contagious and cannot be caught from another person.


Symptoms include a 'flu-like' illness with a rapid onset fever, muscle aches, tiredness, headache, loss of appetite, breathlessness and chest pain and a 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.

All ages can be affected but the disease mainly affects people over 50 years of age, and generally men more than women. Smokers, heavy drinkers and people with a compromised immune system are at a higher risk.


This 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 by wearing a face mask and gloves, open bags away from your face, work in a well-ventilated area and wash your hands when you’re finished.

Further information on working safely with soil, compost and potting mix, and preventing Legionnaires’Disease from cooling towers and evaporative condensers, is available at the Worksafe website:

Further Information

  • Institute for Environmental Science and Research: Legionella numbers on the rise.” 9 October 2018.
    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 (Look for the Legionellosis factsheet under 'L').
    General information, including contact details for the Auckland Disease Investigation Team.
  • Regional Public Health (Greater Wellington region): Legionellosis (Legionnaires’ disease) Fact Sheet
    General information, including contact details for Regional Public Health service.
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