For many people, sharing the spa pool with family and friends is something to enjoy – but not so much if you’re sharing it with unwanted guests such as infectious pneumonia-causing bacteria.

Health New Zealand Te Whatu Ora is encouraging all spa pool owners to regularly clean and maintain their pools, after a recent uptick in cases of people across the motu contracting legionellosis (or legionnaires’ disease) from inadequately maintained spa pools.

“Legionnaires’ disease is a form of pneumonia that results in a chest infection caused by a bacteria called legionella, an environmental organism that lives in moist conditions, such as soil, compost, potting mix, or spa pools and water systems,” says Dr Matt Reid, public health medicine specialist for the National Public Health Service.

Legionella pneumophila.

People can catch the disease by inhaling airborne droplets or particles containing the bacteria. This can cause illness ranging from mild to severe, and can sometimes be fatal.

It is more common in older people, particularly if they smoke, have poor immunity, or have a chronic illness, and those with compromised immune systems are at increased risk of infection.

Reid says recent ESR analysis of people who had contracted legionnaires’ disease during the last year to March 2025, had shown some people had clear links with infected spa pool water.

While most cases of legionellosis in New Zealand come from potting mix or compost, one type of legionellosis is associated with hot water systems.

“In these cases, the testing showed that in eight out of the 10 cases reported, the same type of legionella bacteria was detected in both the infected person and in water samples taken from their spa pools. This means that infected water was the most likely source of infection,” Reid says.

A further investigation by health service staff in the central region, following a recent case of legionnaire’s disease after contact with infected water, found that the spa pool the person had bathed in had not been properly cleaned or maintained over time.

“The 10 cases detected in the year to March is also a significant jump on the three cases recorded for the same period the previous year, hence we are reminding pool owners to make sure that their spa is regularly cleaned, maintained and disinfected using approved products.”

Reid says regular and appropriate cleaning and disinfection are required to prevent the growth of legionellae in private and public spa pools.

Care also needs to be taken when using soil and gardening products such as potting mix, seed raising mix, compost or other similar products, which can harbour the legionella bacteria.

“It’s particularly important to be careful when using these products and not to inhale the dust from them,” Reid says.

“To keep yourself safe, we recommend wearing a disposable face mask and gloves when opening bags of potting mix or other soil products, and to do your potting outside in a well-ventilated area.

“You can also use a sprinkle of water to dampen down potting mix or compost to stop the dust from spreading in the air, and make sure to wash your hands thoroughly after touching potting mix or soil products or after doing any gardening.”

More information about legionellosis (or legionnaires’ disease) and the sources of legionella bacteria can be found here.