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Legionnaires’ disease on the rise

22 November 2019

Gardeners are being warned to protect themselves against Legionnaire’s disease after three cases in just eight days were confirmed in the Tasman region, and after an associated death in Dunedin last month.

Four cases in total have been confirmed in 2019. There have been 53 cases in the region since 2010.

Dr Stephen Bridgman, Clinical Director of Public Health and a Medical Officer of Health, says that Legionnaires’ disease is a serious illness that can cause pneumonia and, in some cases, death.

Potting mix is the most common source of the Legionella bacteria; it’s also present in inadequately-treated spa pools. People most at risk of becoming infected are usually over 50 years of age, smoke, or have chronic illnesses that suppress their immunity.

“Legionnaires’ is not passed from person to person but people can catch it by inhaling soil or compost dust or droplets of water in the air,” Dr Bridgman says.

“Most cases in our region are connected to soil, compost or potting mix. At this time of year, when people are getting into their gardens more we urge people to take care when handling these products,” Dr Bridgman says.

“The Legionella bacteria also lives in warm water, so people who have spa pools need to properly treat their water and maintain their pools.
Maintenance of hot water cylinders and cooling towers is also very important.”
5 simple steps to avoid Legionnaires’ disease when gardening:

1. Open potting mix bags carefully using scissors, rather than by ripping them
2. Wear a disposable face mask and gloves, and open the bag away from your face
3. Do your potting in a well-ventilated area outdoors
4. Dampen down the potting mix or compost with a sprinkle of water to reduce airborne dust
5. Wash your hands thoroughly after handling potting mix, or gardening.

People who own spa pools are reminded to maintain their pools and ensure they are properly treated to prevent the growth of Legionella bacteria.
Symptoms of Legionnaires’ disease include:
Early symptoms can appear 2-14 days after exposure and are similar to the flu:
• fever and chills
• flu-like symptoms and cough
• shortness of breath
• muscle aches, headaches and stomach pain
• vomiting and diarrhoea.

Anyone with these symptoms should see their doctor straight away and let them know you have been handling potting mix, soil or compost recently. Early treatment is effective.

Breakdown of confirmed cases reported to the Nelson Marlborough Medical Officer of Health:
1. Of the 52 confirmed cases of Legionnaires’ diseases between 2010 and 19 November 2019:

• 33 were hospitalised (65% of cases) and hospitalisation occurred in a greater rate among people aged 65+
• slightly more numbers of men (31) were infected than women (21)
• the majority of cases were in people aged 65+ (22), followed by 45-64 (21) and 25-44 (9)
• the majority of cases were attributed to compost or potting mix (29 cases or 56%)

2. Of the four confirmed cases in 2019:
• All were 62 years or older
• All four live in the Tasman region
• All four cases are attributed to potting mix or fertiliser mix

National data: Seasonal increase in cases
1 January to 5 November 2019:
• 50 cases (26 confirmed, 1 probable and 23 under investigation) of legionellosis were notified nationwide in September and October 2019 compared with 29 cases for the same period in 2018.
• 2 cases infected with Legionella longbeachae (associated with compost and potting mix) have died.

For more information
The Safer and Healthier Gardening guide by the Ministry of Health:
WorkSafe NZ’s Working Safely with Soil, Compost and Potting Mix guide:
The Ministry of Health webpage on Legionnaires’ disease:


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