By Belinda Castles
Researcher | Kairangahau
Legionnaires’ disease is caused by Legionella bacteria. It can be severe and in some cases life threatening. Our investigation highlights potential Legionella breeding grounds in your home.
New Zealand has a high incidence of Legionnaires’ disease compared with other countries, with the number of cases fluctuating between 150 and 250 each year. In the past year, there have been 159 hospital admissions due to Legionnaires’ disease recorded.
Typically, the number of cases increases in spring, as people spend more time in the garden. Many cases report using or being exposed to compost or potting mix. However, potting mix and compost aren’t the only culprits.
Legionella bacteria are also found in high numbers in warm water that is left sitting and becomes contaminated. This makes spa pools ideal places for the bacteria to grow. They can also thrive in your hot water system if you turn your cylinder down or off to save money.
Our investigation spotlights three places Legionella bacteria might be lurking around your home.
Health New Zealand | Te Whatu Ora funded this article and our test of potting mix and compost as part of its ongoing efforts to raise awareness about Legionnaires’ disease.
What is Legionnaires’ disease?
Medical officer of health for the National Public Health Service, Dr Cheryl Brunton, said Legionnaires’ disease is a type of pneumonia caused by Legionella bacteria.
“Legionnaires’ disease is more common and more serious in older people, particularly smokers, and people with poor immunity or who have a chronic illness, However, healthy young people have also died from Legionella pneumonia.”
It can be severe and in some cases life threatening. Symptoms are similar to the flu and include:
a dry cough
high fever
chills
shortness of breath
muscle aches
headaches
diarrhoea
vomiting
stomach pain
excessive sweating
mental confusion and disorientation.
The illness worsens over several days. The infection is not contagious.
If you have any of these symptoms and have recently been handling potting mix or compost, see your doctor or healthcare provider as soon as possible. Tell them you have been in contact with potting mix or compost.
Potting mix and compost
If you’re a keen gardener or plant lover, you’ve probably got potting mix or compost in your shed. Both bagged and bulk loads of potting mix and compost can contain Legionella bacteria.
To understand the extent of the risk, we tested samples of 20 potting mix and compost products at accredited lab PHF Science for the presence of Legionella bacteria. Of the 20 samples we tested, four had low levels of the bacteria.
PHF senior scientist David Harte said while it was encouraging that the levels of bacteria found were very low, our test is just a snapshot in time.
“If the test was repeated using different bags of the same potting mix or compost, we are likely to get different results. Some of the products that didn’t contain the bacteria in Consumer’s test, contained Legionella in previous public health surveillance tests the lab has undertaken.”
Mr Harte said consumers should consider there is a risk that any potting mix or compost mixture will contain the bacteria, regardless of the brand. For this reason, we’ve decided not to publish the name of the brands that tested positive in our investigation.
You can find the list of products tested and tips for using potting mix and compost safely in our potting mix and compost investigation.
Spa pools
Legionella bacteria love warm water, and a dirty spa pool is the perfect breeding ground.
In the past 5 years, there have been 62 cases of Legionnaires’ disease in people who have reported exposure to spa pools. You can catch the disease by inhaling airborne droplets of infected water.
In March last year, Health NZ Te Whatu Ora issued a reminder to spa pool owners to regularly clean and maintain their pools using approved products, after noticing an increase in people contracting Legionnaires’ disease linked to infected spa pool water.
Spa pool water treatments and tests: what you need to know.
You’ll need to use several products and tests to keep your spa pool water clean and safe from Legionella and other nasties.
Test the water regularly, so you know which products to use. You can buy test strips to check the different indicators, such as pH and water hardness.
Check the chemical levels in the water at least once a week.
If your spa has lots of bathers, you may need to increase the frequency of testing.
Types of treatments
Sanitizer: used to disinfect spa water. Sanitizers include chlorine, bromine and hydrogen peroxide.
Before you buy, check the product meets the New Zealand Pool Water Quality standard. We found some hydrogen peroxide products that didn’t have the required dosage to meet the standard in our 2023 investigation into spa pool treatments.
Be wary of alternative treatment options, like silver or ‘natural’ or ‘eco-friendly’ options. The spa pool expert we spoke to said these types of products shouldn’t be used as a standalone treatment to keep spa pool water clean. They’re also unlikely to meet the New Zealand standard.
Shock treatment: if your spa has had more bathers than usual, a shock treatment (like a dose of chlorine) can help clear the water and kick-start the sanitizer.
Enzymes: can help keep spa pool water clean but should be used in conjunction with a sanitizer. Enzymes work by helping break down organic matter in the water, like lotions, sweat and body oils.
Types of tests
Water hardness: refers to the level of calcium in the pool. If you have too much, the water will be hard, and if you don’t have enough, it’ll be soft. If the level is too high, you’ll need to empty the spa and give it a good clean. If it’s too soft, the water will feel slimy and create a foam, which can corrode the pool.
Alkalinity: measures the level of carbonates and bicarbonates in the pool, which helps to stabilise the pH.
pH level: if the pH level in your spa is too high the chlorine won’t work as well as it should. It’s also important that the pH of a bather’s body is in the same range as the pool water to avoid irritation to the skin and eyes from the sanitizer. The NZ Safety Standard recommends a pH between 7.2 and 8.
Your local spa pool expert will be able to advise you what products to use depending on your test results.
Keep your filters clean
Along with chemical treatment, spas also need filtration to keep the water clean. Clean the filters when you check the chemicals.
Filters act like sieves to remove particles from the water. The efficiency of the filter can also depend on the pump. If your spa has a low-flow pump, the water isn’t going through the filter as often, and so isn’t cleaning the water as often.
Change your spa water
How often you need to change the water in your spa depends on:
how often you use it
whether users have a shower before jumping in
how well you keep the water chemically balanced and clean.
The New Zealand Standard for pool water quality recommends changing the water every month. Once empty, the spa will need a good scrub before being refilled.
Because chemical treatments are used to keep spa pool water clean, the water needs to be disposed of through the sewer system (not a storm drain).
Hot water systems
Heating your water accounts for about 30% of household energy usage. So, when seasonal power bills start to climb, it can be tempting to turn down your hot water or turn it off to save money.
But Health NZ Te Whatu Ora warns against this money saving hack. Heat is the simplest way to stop Legionella bacteria growing and it’s recommended hot water should be stored at a minimum of 60°C.
Here’s some other ways to save money on your hot water without turning the temperature down.
Insulate your cylinder: cylinders and pipes installed before 2002 generally aren’t well insulated, but adding insulation later needn’t be expensive. You can buy cylinder wraps from hardware stores for about $60 and pipe insulation from $5 per metre (ask for ‘thermal pipe lagging’). New cylinders tend to be better insulated, so lose less heat, but can still benefit from an insulating wrap.
Install an efficient showerhead: the rule of thumb is your shower is wasting water if it fills a 10L bucket in less than a minute. Replace your inefficient showerhead with one with a flow rate of less than 9L per minute. The showerhead will save hot water while still delivering a comfortable and effective shower.
Wash your clothes in cold water: a cold wash is all you need for most loads and will cost you a lot less than a warm one.
Compare power companies at Powerswitch: Powerswitch is Consumer NZ’s free price comparison website that helps you find the cheapest power and gas plan. Last year, the average saving for Powerswitch users was $394 per year.
