The spa at Auckland's Tepid Baths had been shut down after water tested positive for Legionella bacterium - which causes Legionnaires' disease.
An Auckland Council spokeswoman said the spa was closed last Thursday after a positive test for the bacterium - which grows best in warm water.
In December the spa in Manurewa was closed after water tested positive for the same bacteria. The pool has since been drained, "deep cleaned" and re-opened after the return of negative test results.
Due to the discovery of two cases of the bacteria being present in a three month period, the council has taken a precautionary approach across all of the city's 18 spas - with additional chlorination and chemical cleaning being undertaken.
Testing for the bacteria is not common practice across the pools, but was done after a person with symptoms of an infection said they had been at the pool.
Auckland Council's leisure manager, Rob McGee, said in both cases the team acted on advice from council's environmental health team and the Auckland Regional Public Health Service and immediately closed and treated the spa pools.
"As this is the second event in a three-month period, we have taken the additional precautionary step of treating all 18 of our spa pools.
"On top of that, over the next few weeks, we'll be working to ensure that every spa pool in the network undergoes an extra deep clean," said Mr McGee.
He said the council's processes exceed New Zealand standards and was confident the risk to public health was low.
A person with Legionnaire's disease was admitted to North Shore Hospital on October 3 last year, Medical Officer of Health at Auckland Regional Public Health Service (ARPHS) Dr Simon Baker said.
From there, the person was interviewed by ARPHS disease investigators who identified places where the bacterium may have come from - including the Tepid Baths, which tested positive.
Dr Baker said no other cases of Legionnaires' disease linked to the Tepid Baths has been reported since records began.
No other cases had been identified which were linked to the individual, he said.
"Legionnaire's disease can't be passed from person to person."
He said no other closures or further sites were investigated in relation to the case, which Dr Baker said was "almost identical" to the scenario that resulted Legionella being found at the spa at the Manurewa Pool and Leisure Centre in December.
Dr Baker said about 60 cases of legionnaires' disease were identified in the Auckland region each year, the equivalent of three people per 100,000 annually, and the bacterium was common in New Zealand.
Contraction of the disease was more common as people got older, as well as being more common among men, smokers, people with chronic illnesses, chest and heart disease, or on immune suppressing drugs.
What is Legionella?
• Legionella is a type of bacterium found naturally in fresh water.
• When people are exposed to the bacterium, it can cause Legionnaires' disease and Pontiac fever).
• The bacterium grows best in warm water, like that found in spa pools, cooling towers (air-conditioning units for large buildings), hot-water tanks, large plumbing systems and decorative fountains.
• People are exposed to Legionella when they breathe in a mist or vapour containing the bacteria.
• Less commonly, Legionella can be transmitted when water "goes down the wrong pipe," into the windpipe and lungs instead of down the digestive tract.
• Legionella cannot spread from one person to another.
• Most people exposed to the bacteria do not become ill.
• If you have reason to believe you were exposed to the bacteria, talk to your doctor or local health department.
What is Legionnaires' Disease?
• Legionnaires' disease is a very serious type of pneumonia (lung infection).
• Signs and symptoms include cough, shortness of breath, muscle aches, headache and high fever.
• The disease is treated with antibiotics.
• Most people need hospital care but make a full recovery. However, about one out of 10 people who get Legionnaires' disease will die from the infection.
• Most healthy people do not get the disease after being exposed to Legionella.
• Risk factors that increase your chances of getting sick include being 50 years or older, being a current or former smoker, having chronic lung disease such as emphysema or chronic obstructive pulmonary disease, having a weakened immune system from diseases like cancer, diabetes, or kidney failure or from taking medication that weakens your immune system.